- 根目录:
- mm
- vmscan.c
C++程序
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/*
* linux/mm/vmscan.c
*
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
*
* Swap reorganised 29.12.95, Stephen Tweedie.
* kswapd added: 7.1.96 sct
* Removed kswapd_ctl limits, and swap out as many pages as needed
* to bring the system back to freepages.high: 2.4.97, Rik van Riel.
* Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
* Multiqueue VM started 5.8.00, Rik van Riel.
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/gfp.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/highmem.h>
#include <linux/vmstat.h>
#include <linux/file.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h> /* for try_to_release_page(),
buffer_heads_over_limit */
#include <linux/mm_inline.h>
#include <linux/pagevec.h>
#include <linux/backing-dev.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/compaction.h>
#include <linux/notifier.h>
#include <linux/rwsem.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/memcontrol.h>
#include <linux/delayacct.h>
#include <linux/sysctl.h>
#include <linux/oom.h>
#include <linux/prefetch.h>
#include <asm/tlbflush.h>
#include <asm/div64.h>
#include <linux/swapops.h>
#include "internal.h"
#define CREATE_TRACE_POINTS
#include <trace/events/vmscan.h>
/*
* reclaim_mode determines how the inactive list is shrunk
* RECLAIM_MODE_SINGLE: Reclaim only order-0 pages
* RECLAIM_MODE_ASYNC: Do not block
* RECLAIM_MODE_SYNC: Allow blocking e.g. call wait_on_page_writeback
* RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference
* page from the LRU and reclaim all pages within a
* naturally aligned range
* RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of
* order-0 pages and then compact the zone
*/
typedef unsigned __bitwise__ reclaim_mode_t;
#define RECLAIM_MODE_SINGLE ((__force reclaim_mode_t)0x01u)
#define RECLAIM_MODE_ASYNC ((__force reclaim_mode_t)0x02u)
#define RECLAIM_MODE_SYNC ((__force reclaim_mode_t)0x04u)
#define RECLAIM_MODE_LUMPYRECLAIM ((__force reclaim_mode_t)0x08u)
#define RECLAIM_MODE_COMPACTION ((__force reclaim_mode_t)0x10u)
struct scan_control {
/* Incremented by the number of inactive pages that were scanned */
unsigned long nr_scanned;
/* Number of pages freed so far during a call to shrink_zones() */
unsigned long nr_reclaimed;
/* How many pages shrink_list() should reclaim */
unsigned long nr_to_reclaim;
unsigned long hibernation_mode;
/* This context's GFP mask */
gfp_t gfp_mask;
int may_writepage;
/* Can mapped pages be reclaimed? */
int may_unmap;
/* Can pages be swapped as part of reclaim? */
int may_swap;
int swappiness;
int order;
/*
* Intend to reclaim enough continuous memory rather than reclaim
* enough amount of memory. i.e, mode for high order allocation.
*/
reclaim_mode_t reclaim_mode;
/* Which cgroup do we reclaim from */
struct mem_cgroup *mem_cgroup;
/*
* Nodemask of nodes allowed by the caller. If NULL, all nodes
* are scanned.
*/
nodemask_t *nodemask;
};
#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
#ifdef ARCH_HAS_PREFETCH
#define prefetch_prev_lru_page(_page, _base, _field) \
do { \
if ((_page)->lru.prev != _base) { \
struct page *prev; \
\
prev = lru_to_page(&(_page->lru)); \
prefetch(&prev->_field); \
} \
} while (0)
#else
#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
#endif
#ifdef ARCH_HAS_PREFETCHW
#define prefetchw_prev_lru_page(_page, _base, _field) \
do { \
if ((_page)->lru.prev != _base) { \
struct page *prev; \
\
prev = lru_to_page(&(_page->lru)); \
prefetchw(&prev->_field); \
} \
} while (0)
#else
#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
#endif
/*
* From 0 .. 100. Higher means more swappy.
*/
int vm_swappiness = 60;
long vm_total_pages; /* The total number of pages which the VM controls */
static LIST_HEAD(shrinker_list);
static DECLARE_RWSEM(shrinker_rwsem);
#ifdef CONFIG_CGROUP_MEM_RES_CTLR
#define scanning_global_lru(sc) (!(sc)->mem_cgroup)
#else
#define scanning_global_lru(sc) (1)
#endif
static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
struct scan_control *sc)
{
if (!scanning_global_lru(sc))
return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);
return &zone->reclaim_stat;
}
static unsigned long zone_nr_lru_pages(struct zone *zone,
struct scan_control *sc, enum lru_list lru)
{
if (!scanning_global_lru(sc))
return mem_cgroup_zone_nr_lru_pages(sc->mem_cgroup, zone, lru);
return zone_page_state(zone, NR_LRU_BASE + lru);
}
/*
* Add a shrinker callback to be called from the vm
*/
void register_shrinker(struct shrinker *shrinker)
{
shrinker->nr = 0;
down_write(&shrinker_rwsem);
list_add_tail(&shrinker->list, &shrinker_list);
up_write(&shrinker_rwsem);
}
EXPORT_SYMBOL(register_shrinker);
/*
* Remove one
*/
void unregister_shrinker(struct shrinker *shrinker)
{
down_write(&shrinker_rwsem);
list_del(&shrinker->list);
up_write(&shrinker_rwsem);
}
EXPORT_SYMBOL(unregister_shrinker);
static inline int do_shrinker_shrink(struct shrinker *shrinker,
struct shrink_control *sc,
unsigned long nr_to_scan)
{
sc->nr_to_scan = nr_to_scan;
return (*shrinker->shrink)(shrinker, sc);
}
#define SHRINK_BATCH 128
/*
* Call the shrink functions to age shrinkable caches
*
* Here we assume it costs one seek to replace a lru page and that it also
* takes a seek to recreate a cache object. With this in mind we age equal
* percentages of the lru and ageable caches. This should balance the seeks
* generated by these structures.
*
* If the vm encountered mapped pages on the LRU it increase the pressure on
* slab to avoid swapping.
*
* We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
*
* `lru_pages' represents the number of on-LRU pages in all the zones which
* are eligible for the caller's allocation attempt. It is used for balancing
* slab reclaim versus page reclaim.
*
* Returns the number of slab objects which we shrunk.
*/
unsigned long shrink_slab(struct shrink_control *shrink,
unsigned long nr_pages_scanned,
unsigned long lru_pages)
{
struct shrinker *shrinker;
unsigned long ret = 0;
if (nr_pages_scanned == 0)
nr_pages_scanned = SWAP_CLUSTER_MAX;
if (!down_read_trylock(&shrinker_rwsem)) {
/* Assume we'll be able to shrink next time */
ret = 1;
goto out;
}
list_for_each_entry(shrinker, &shrinker_list, list) {
unsigned long long delta;
long total_scan;
long max_pass;
int shrink_ret = 0;
long nr;
long new_nr;
long batch_size = shrinker->batch ? shrinker->batch
: SHRINK_BATCH;
max_pass = do_shrinker_shrink(shrinker, shrink, 0);
if (max_pass <= 0)
continue;
/*
* copy the current shrinker scan count into a local variable
* and zero it so that other concurrent shrinker invocations
* don't also do this scanning work.
*/
do {
nr = shrinker->nr;
} while (cmpxchg(&shrinker->nr, nr, 0) != nr);
total_scan = nr;
delta = (4 * nr_pages_scanned) / shrinker->seeks;
delta *= max_pass;
do_div(delta, lru_pages + 1);
total_scan += delta;
if (total_scan < 0) {
printk(KERN_ERR "shrink_slab: %pF negative objects to "
"delete nr=%ld\n",
shrinker->shrink, total_scan);
total_scan = max_pass;
}
/*
* We need to avoid excessive windup on filesystem shrinkers
* due to large numbers of GFP_NOFS allocations causing the
* shrinkers to return -1 all the time. This results in a large
* nr being built up so when a shrink that can do some work
* comes along it empties the entire cache due to nr >>>
* max_pass. This is bad for sustaining a working set in
* memory.
*
* Hence only allow the shrinker to scan the entire cache when
* a large delta change is calculated directly.
*/
if (delta < max_pass / 4)
total_scan = min(total_scan, max_pass / 2);
/*
* Avoid risking looping forever due to too large nr value:
* never try to free more than twice the estimate number of
* freeable entries.
*/
if (total_scan > max_pass * 2)
total_scan = max_pass * 2;
trace_mm_shrink_slab_start(shrinker, shrink, nr,
nr_pages_scanned, lru_pages,
max_pass, delta, total_scan);
while (total_scan >= batch_size) {
int shrink_ret;
int nr_before;
nr_before = do_shrinker_shrink(shrinker, shrink, 0);
shrink_ret = do_shrinker_shrink(shrinker, shrink,
batch_size);
if (shrink_ret == -1)
break;
if (shrink_ret < nr_before)
ret += nr_before - shrink_ret;
count_vm_events(SLABS_SCANNED, batch_size);
total_scan -= batch_size;
cond_resched();
}
/*
* move the unused scan count back into the shrinker in a
* manner that handles concurrent updates. If we exhausted the
* scan, there is no need to do an update.
*/
do {
nr = shrinker->nr;
new_nr = total_scan + nr;
if (total_scan <= 0)
break;
} while (cmpxchg(&shrinker->nr, nr, new_nr) != nr);
trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
}
up_read(&shrinker_rwsem);
out:
cond_resched();
return ret;
}
static void set_reclaim_mode(int priority, struct scan_control *sc,
bool sync)
{
reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC;
/*
* Initially assume we are entering either lumpy reclaim or
* reclaim/compaction.Depending on the order, we will either set the
* sync mode or just reclaim order-0 pages later.
*/
if (COMPACTION_BUILD)
sc->reclaim_mode = RECLAIM_MODE_COMPACTION;
else
sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM;
/*
* Avoid using lumpy reclaim or reclaim/compaction if possible by
* restricting when its set to either costly allocations or when
* under memory pressure
*/
if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
sc->reclaim_mode |= syncmode;
else if (sc->order && priority < DEF_PRIORITY - 2)
sc->reclaim_mode |= syncmode;
else
sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
}
static void reset_reclaim_mode(struct scan_control *sc)
{
sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
}
static inline int is_page_cache_freeable(struct page *page)
{
/*
* A freeable page cache page is referenced only by the caller
* that isolated the page, the page cache radix tree and
* optional buffer heads at page->private.
*/
return page_count(page) - page_has_private(page) == 2;
}
static int may_write_to_queue(struct backing_dev_info *bdi,
struct scan_control *sc)
{
if (current->flags & PF_SWAPWRITE)
return 1;
if (!bdi_write_congested(bdi))
return 1;
if (bdi == current->backing_dev_info)
return 1;
/* lumpy reclaim for hugepage often need a lot of write */
if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
return 1;
return 0;
}
/*
* We detected a synchronous write error writing a page out. Probably
* -ENOSPC. We need to propagate that into the address_space for a subsequent
* fsync(), msync() or close().
*
* The tricky part is that after writepage we cannot touch the mapping: nothing
* prevents it from being freed up. But we have a ref on the page and once
* that page is locked, the mapping is pinned.
*
* We're allowed to run sleeping lock_page() here because we know the caller has
* __GFP_FS.
*/
static void handle_write_error(struct address_space *mapping,
struct page *page, int error)
{
lock_page(page);
if (page_mapping(page) == mapping)
mapping_set_error(mapping, error);
unlock_page(page);
}
/* possible outcome of pageout() */
typedef enum {
/* failed to write page out, page is locked */
PAGE_KEEP,
/* move page to the active list, page is locked */
PAGE_ACTIVATE,
/* page has been sent to the disk successfully, page is unlocked */
PAGE_SUCCESS,
/* page is clean and locked */
PAGE_CLEAN,
} pageout_t;
/*
* pageout is called by shrink_page_list() for each dirty page.
* Calls ->writepage().
*/
static pageout_t pageout(struct page *page, struct address_space *mapping,
struct scan_control *sc)
{
/*
* If the page is dirty, only perform writeback if that write
* will be non-blocking. To prevent this allocation from being
* stalled by pagecache activity. But note that there may be
* stalls if we need to run get_block(). We could test
* PagePrivate for that.
*
* If this process is currently in __generic_file_aio_write() against
* this page's queue, we can perform writeback even if that
* will block.
*
* If the page is swapcache, write it back even if that would
* block, for some throttling. This happens by accident, because
* swap_backing_dev_info is bust: it doesn't reflect the
* congestion state of the swapdevs. Easy to fix, if needed.
*/
if (!is_page_cache_freeable(page))
return PAGE_KEEP;
if (!mapping) {
/*
* Some data journaling orphaned pages can have
* page->mapping == NULL while being dirty with clean buffers.
*/
if (page_has_private(page)) {
if (try_to_free_buffers(page)) {
ClearPageDirty(page);
printk("%s: orphaned page\n", __func__);
return PAGE_CLEAN;
}
}
return PAGE_KEEP;
}
if (mapping->a_ops->writepage == NULL)
return PAGE_ACTIVATE;
if (!may_write_to_queue(mapping->backing_dev_info, sc))
return PAGE_KEEP;
if (clear_page_dirty_for_io(page)) {
int res;
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
.nr_to_write = SWAP_CLUSTER_MAX,
.range_start = 0,
.range_end = LLONG_MAX,
.for_reclaim = 1,
};
SetPageReclaim(page);
res = mapping->a_ops->writepage(page, &wbc);
if (res < 0)
handle_write_error(mapping, page, res);
if (res == AOP_WRITEPAGE_ACTIVATE) {
ClearPageReclaim(page);
return PAGE_ACTIVATE;
}
/*
* Wait on writeback if requested to. This happens when
* direct reclaiming a large contiguous area and the
* first attempt to free a range of pages fails.
*/
if (PageWriteback(page) &&
(sc->reclaim_mode & RECLAIM_MODE_SYNC))
wait_on_page_writeback(page);
if (!PageWriteback(page)) {
/* synchronous write or broken a_ops? */
ClearPageReclaim(page);
}
trace_mm_vmscan_writepage(page,
trace_reclaim_flags(page, sc->reclaim_mode));
inc_zone_page_state(page, NR_VMSCAN_WRITE);
return PAGE_SUCCESS;
}
return PAGE_CLEAN;
}
/*
* Same as remove_mapping, but if the page is removed from the mapping, it
* gets returned with a refcount of 0.
*/
static int __remove_mapping(struct address_space *mapping, struct page *page)
{
BUG_ON(!PageLocked(page));
BUG_ON(mapping != page_mapping(page));
spin_lock_irq(&mapping->tree_lock);
/*
* The non racy check for a busy page.
*
* Must be careful with the order of the tests. When someone has
* a ref to the page, it may be possible that they dirty it then
* drop the reference. So if PageDirty is tested before page_count
* here, then the following race may occur:
*
* get_user_pages(&page);
* [user mapping goes away]
* write_to(page);
* !PageDirty(page) [good]
* SetPageDirty(page);
* put_page(page);
* !page_count(page) [good, discard it]
*
* [oops, our write_to data is lost]
*
* Reversing the order of the tests ensures such a situation cannot
* escape unnoticed. The smp_rmb is needed to ensure the page->flags
* load is not satisfied before that of page->_count.
*
* Note that if SetPageDirty is always performed via set_page_dirty,
* and thus under tree_lock, then this ordering is not required.
*/
if (!page_freeze_refs(page, 2))
goto cannot_free;
/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
if (unlikely(PageDirty(page))) {
page_unfreeze_refs(page, 2);
goto cannot_free;
}
if (PageSwapCache(page)) {
swp_entry_t swap = { .val = page_private(page) };
__delete_from_swap_cache(page);
spin_unlock_irq(&mapping->tree_lock);
swapcache_free(swap, page);
} else {
void (*freepage)(struct page *);
freepage = mapping->a_ops->freepage;
__delete_from_page_cache(page);
spin_unlock_irq(&mapping->tree_lock);
mem_cgroup_uncharge_cache_page(page);
if (freepage != NULL)
freepage(page);
}
return 1;
cannot_free:
spin_unlock_irq(&mapping->tree_lock);
return 0;
}
/*
* Attempt to detach a locked page from its ->mapping. If it is dirty or if
* someone else has a ref on the page, abort and return 0. If it was
* successfully detached, return 1. Assumes the caller has a single ref on
* this page.
*/
int remove_mapping(struct address_space *mapping, struct page *page)
{
if (__remove_mapping(mapping, page)) {
/*
* Unfreezing the refcount with 1 rather than 2 effectively
* drops the pagecache ref for us without requiring another
* atomic operation.
*/
page_unfreeze_refs(page, 1);
return 1;
}
return 0;
}
/**
* putback_lru_page - put previously isolated page onto appropriate LRU list
* @page: page to be put back to appropriate lru list
*
* Add previously isolated @page to appropriate LRU list.
* Page may still be unevictable for other reasons.
*
* lru_lock must not be held, interrupts must be enabled.
*/
void putback_lru_page(struct page *page)
{
int lru;
int active = !!TestClearPageActive(page);
int was_unevictable = PageUnevictable(page);
VM_BUG_ON(PageLRU(page));
redo:
ClearPageUnevictable(page);
if (page_evictable(page, NULL)) {
/*
* For evictable pages, we can use the cache.
* In event of a race, worst case is we end up with an
* unevictable page on [in]active list.
* We know how to handle that.
*/
lru = active + page_lru_base_type(page);
lru_cache_add_lru(page, lru);
} else {
/*
* Put unevictable pages directly on zone's unevictable
* list.
*/
lru = LRU_UNEVICTABLE;
add_page_to_unevictable_list(page);
/*
* When racing with an mlock clearing (page is
* unlocked), make sure that if the other thread does
* not observe our setting of PG_lru and fails
* isolation, we see PG_mlocked cleared below and move
* the page back to the evictable list.
*
* The other side is TestClearPageMlocked().
*/
smp_mb();
}
/*
* page's status can change while we move it among lru. If an evictable
* page is on unevictable list, it never be freed. To avoid that,
* check after we added it to the list, again.
*/
if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
if (!isolate_lru_page(page)) {
put_page(page);
goto redo;
}
/* This means someone else dropped this page from LRU
* So, it will be freed or putback to LRU again. There is
* nothing to do here.
*/
}
if (was_unevictable && lru != LRU_UNEVICTABLE)
count_vm_event(UNEVICTABLE_PGRESCUED);
else if (!was_unevictable && lru == LRU_UNEVICTABLE)
count_vm_event(UNEVICTABLE_PGCULLED);
put_page(page); /* drop ref from isolate */
}
enum page_references {
PAGEREF_RECLAIM,
PAGEREF_RECLAIM_CLEAN,
PAGEREF_KEEP,
PAGEREF_ACTIVATE,
};
static enum page_references page_check_references(struct page *page,
struct scan_control *sc)
{
int referenced_ptes, referenced_page;
unsigned long vm_flags;
referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
referenced_page = TestClearPageReferenced(page);
/* Lumpy reclaim - ignore references */
if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
return PAGEREF_RECLAIM;
/*
* Mlock lost the isolation race with us. Let try_to_unmap()
* move the page to the unevictable list.
*/
if (vm_flags & VM_LOCKED)
return PAGEREF_RECLAIM;
if (referenced_ptes) {
if (PageSwapBacked(page))
return PAGEREF_ACTIVATE;
/*
* All mapped pages start out with page table
* references from the instantiating fault, so we need
* to look twice if a mapped file page is used more
* than once.
*
* Mark it and spare it for another trip around the
* inactive list. Another page table reference will
* lead to its activation.
*
* Note: the mark is set for activated pages as well
* so that recently deactivated but used pages are
* quickly recovered.
*/
SetPageReferenced(page);
if (referenced_page || referenced_ptes > 1)
return PAGEREF_ACTIVATE;
/*
* Activate file-backed executable pages after first usage.
*/
if (vm_flags & VM_EXEC)
return PAGEREF_ACTIVATE;
return PAGEREF_KEEP;
}
/* Reclaim if clean, defer dirty pages to writeback */
if (referenced_page && !PageSwapBacked(page))
return PAGEREF_RECLAIM_CLEAN;
return PAGEREF_RECLAIM;
}
static noinline_for_stack void free_page_list(struct list_head *free_pages)
{
struct pagevec freed_pvec;
struct page *page, *tmp;
pagevec_init(&freed_pvec, 1);
list_for_each_entry_safe(page, tmp, free_pages, lru) {
list_del(&page->lru);
if (!pagevec_add(&freed_pvec, page)) {
__pagevec_free(&freed_pvec);
pagevec_reinit(&freed_pvec);
}
}
pagevec_free(&freed_pvec);
}
/*
* shrink_page_list() returns the number of reclaimed pages
*/
static unsigned long shrink_page_list(struct list_head *page_list,
struct zone *zone,
struct scan_control *sc)
{
LIST_HEAD(ret_pages);
LIST_HEAD(free_pages);
int pgactivate = 0;
unsigned long nr_dirty = 0;
unsigned long nr_congested = 0;
unsigned long nr_reclaimed = 0;
cond_resched();
while (!list_empty(page_list)) {
enum page_references references;
struct address_space *mapping;
struct page *page;
int may_enter_fs;
cond_resched();
page = lru_to_page(page_list);
list_del(&page->lru);
if (!trylock_page(page))
goto keep;
VM_BUG_ON(PageActive(page));
VM_BUG_ON(page_zone(page) != zone);
sc->nr_scanned++;
if (unlikely(!page_evictable(page, NULL)))
goto cull_mlocked;
if (!sc->may_unmap && page_mapped(page))
goto keep_locked;
/* Double the slab pressure for mapped and swapcache pages */
if (page_mapped(page) || PageSwapCache(page))
sc->nr_scanned++;
may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
if (PageWriteback(page)) {
/*
* Synchronous reclaim is performed in two passes,
* first an asynchronous pass over the list to
* start parallel writeback, and a second synchronous
* pass to wait for the IO to complete. Wait here
* for any page for which writeback has already
* started.
*/
if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) &&
may_enter_fs)
wait_on_page_writeback(page);
else {
unlock_page(page);
goto keep_lumpy;
}
}
references = page_check_references(page, sc);
switch (references) {
case PAGEREF_ACTIVATE:
goto activate_locked;
case PAGEREF_KEEP:
goto keep_locked;
case PAGEREF_RECLAIM:
case PAGEREF_RECLAIM_CLEAN:
; /* try to reclaim the page below */
}
/*
* Anonymous process memory has backing store?
* Try to allocate it some swap space here.
*/
if (PageAnon(page) && !PageSwapCache(page)) {
if (!(sc->gfp_mask & __GFP_IO))
goto keep_locked;
if (!add_to_swap(page))
goto activate_locked;
may_enter_fs = 1;
}
mapping = page_mapping(page);
/*
* The page is mapped into the page tables of one or more
* processes. Try to unmap it here.
*/
if (page_mapped(page) && mapping) {
switch (try_to_unmap(page, TTU_UNMAP)) {
case SWAP_FAIL:
goto activate_locked;
case SWAP_AGAIN:
goto keep_locked;
case SWAP_MLOCK:
goto cull_mlocked;
case SWAP_SUCCESS:
; /* try to free the page below */
}
}
if (PageDirty(page)) {
nr_dirty++;
if (references == PAGEREF_RECLAIM_CLEAN)
goto keep_locked;
if (!may_enter_fs)
goto keep_locked;
if (!sc->may_writepage)
goto keep_locked;
/* Page is dirty, try to write it out here */
switch (pageout(page, mapping, sc)) {
case PAGE_KEEP:
nr_congested++;
goto keep_locked;
case PAGE_ACTIVATE:
goto activate_locked;
case PAGE_SUCCESS:
if (PageWriteback(page))
goto keep_lumpy;
if (PageDirty(page))
goto keep;
/*
* A synchronous write - probably a ramdisk. Go
* ahead and try to reclaim the page.
*/
if (!trylock_page(page))
goto keep;
if (PageDirty(page) || PageWriteback(page))
goto keep_locked;
mapping = page_mapping(page);
case PAGE_CLEAN:
; /* try to free the page below */
}
}
/*
* If the page has buffers, try to free the buffer mappings
* associated with this page. If we succeed we try to free
* the page as well.
*
* We do this even if the page is PageDirty().
* try_to_release_page() does not perform I/O, but it is
* possible for a page to have PageDirty set, but it is actually
* clean (all its buffers are clean). This happens if the
* buffers were written out directly, with submit_bh(). ext3
* will do this, as well as the blockdev mapping.
* try_to_release_page() will discover that cleanness and will
* drop the buffers and mark the page clean - it can be freed.
*
* Rarely, pages can have buffers and no ->mapping. These are
* the pages which were not successfully invalidated in
* truncate_complete_page(). We try to drop those buffers here
* and if that worked, and the page is no longer mapped into
* process address space (page_count == 1) it can be freed.
* Otherwise, leave the page on the LRU so it is swappable.
*/
if (page_has_private(page)) {
if (!try_to_release_page(page, sc->gfp_mask))
goto activate_locked;
if (!mapping && page_count(page) == 1) {
unlock_page(page);
if (put_page_testzero(page))
goto free_it;
else {
/*
* rare race with speculative reference.
* the speculative reference will free
* this page shortly, so we may
* increment nr_reclaimed here (and
* leave it off the LRU).
*/
nr_reclaimed++;
continue;
}
}
}
if (!mapping || !__remove_mapping(mapping, page))
goto keep_locked;
/*
* At this point, we have no other references and there is
* no way to pick any more up (removed from LRU, removed
* from pagecache). Can use non-atomic bitops now (and
* we obviously don't have to worry about waking up a process
* waiting on the page lock, because there are no references.
*/
__clear_page_locked(page);
free_it:
nr_reclaimed++;
/*
* Is there need to periodically free_page_list? It would
* appear not as the counts should be low
*/
list_add(&page->lru, &free_pages);
continue;
cull_mlocked:
if (PageSwapCache(page))
try_to_free_swap(page);
unlock_page(page);
putback_lru_page(page);
reset_reclaim_mode(sc);
continue;
activate_locked:
/* Not a candidate for swapping, so reclaim swap space. */
if (PageSwapCache(page) && vm_swap_full())
try_to_free_swap(page);
VM_BUG_ON(PageActive(page));
SetPageActive(page);
pgactivate++;
keep_locked:
unlock_page(page);
keep:
reset_reclaim_mode(sc);
keep_lumpy:
list_add(&page->lru, &ret_pages);
VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
}
/*
* Tag a zone as congested if all the dirty pages encountered were
* backed by a congested BDI. In this case, reclaimers should just
* back off and wait for congestion to clear because further reclaim
* will encounter the same problem
*/
if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc))
zone_set_flag(zone, ZONE_CONGESTED);
free_page_list(&free_pages);
list_splice(&ret_pages, page_list);
count_vm_events(PGACTIVATE, pgactivate);
return nr_reclaimed;
}
/*
* Attempt to remove the specified page from its LRU. Only take this page
* if it is of the appropriate PageActive status. Pages which are being
* freed elsewhere are also ignored.
*
* page: page to consider
* mode: one of the LRU isolation modes defined above
*
* returns 0 on success, -ve errno on failure.
*/
int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
{
bool all_lru_mode;
int ret = -EINVAL;
/* Only take pages on the LRU. */
if (!PageLRU(page))
return ret;
all_lru_mode = (mode & (ISOLATE_ACTIVE|ISOLATE_INACTIVE)) ==
(ISOLATE_ACTIVE|ISOLATE_INACTIVE);
/*
* When checking the active state, we need to be sure we are
* dealing with comparible boolean values. Take the logical not
* of each.
*/
if (!all_lru_mode && !PageActive(page) != !(mode & ISOLATE_ACTIVE))
return ret;
if (!all_lru_mode && !!page_is_file_cache(page) != file)
return ret;
/*
* When this function is being called for lumpy reclaim, we
* initially look into all LRU pages, active, inactive and
* unevictable; only give shrink_page_list evictable pages.
*/
if (PageUnevictable(page))
return ret;
ret = -EBUSY;
/*
* To minimise LRU disruption, the caller can indicate that it only
* wants to isolate pages it will be able to operate on without
* blocking - clean pages for the most part.
*
* ISOLATE_CLEAN means that only clean pages should be isolated. This
* is used by reclaim when it is cannot write to backing storage
*
* ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
* that it is possible to migrate without blocking
*/
if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
/* All the caller can do on PageWriteback is block */
if (PageWriteback(page))
return ret;
if (PageDirty(page)) {
struct address_space *mapping;
/* ISOLATE_CLEAN means only clean pages */
if (mode & ISOLATE_CLEAN)
return ret;
/*
* Only pages without mappings or that have a
* ->migratepage callback are possible to migrate
* without blocking
*/
mapping = page_mapping(page);
if (mapping && !mapping->a_ops->migratepage)
return ret;
}
}
if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
return ret;
if (likely(get_page_unless_zero(page))) {
/*
* Be careful not to clear PageLRU until after we're
* sure the page is not being freed elsewhere -- the
* page release code relies on it.
*/
ClearPageLRU(page);
ret = 0;
}
return ret;
}
/*
* zone->lru_lock is heavily contended. Some of the functions that
* shrink the lists perform better by taking out a batch of pages
* and working on them outside the LRU lock.
*
* For pagecache intensive workloads, this function is the hottest
* spot in the kernel (apart from copy_*_user functions).
*
* Appropriate locks must be held before calling this function.
*
* @nr_to_scan: The number of pages to look through on the list.
* @src: The LRU list to pull pages off.
* @dst: The temp list to put pages on to.
* @scanned: The number of pages that were scanned.
* @order: The caller's attempted allocation order
* @mode: One of the LRU isolation modes
* @file: True [1] if isolating file [!anon] pages
*
* returns how many pages were moved onto *@dst.
*/
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
struct list_head *src, struct list_head *dst,
unsigned long *scanned, int order, isolate_mode_t mode,
int file)
{
unsigned long nr_taken = 0;
unsigned long nr_lumpy_taken = 0;
unsigned long nr_lumpy_dirty = 0;
unsigned long nr_lumpy_failed = 0;
unsigned long scan;
for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
struct page *page;
unsigned long pfn;
unsigned long end_pfn;
unsigned long page_pfn;
int zone_id;
page = lru_to_page(src);
prefetchw_prev_lru_page(page, src, flags);
VM_BUG_ON(!PageLRU(page));
switch (__isolate_lru_page(page, mode, file)) {
case 0:
list_move(&page->lru, dst);
mem_cgroup_del_lru(page);
nr_taken += hpage_nr_pages(page);
break;
case -EBUSY:
/* else it is being freed elsewhere */
list_move(&page->lru, src);
mem_cgroup_rotate_lru_list(page, page_lru(page));
continue;
default:
BUG();
}
if (!order)
continue;
/*
* Attempt to take all pages in the order aligned region
* surrounding the tag page. Only take those pages of
* the same active state as that tag page. We may safely
* round the target page pfn down to the requested order
* as the mem_map is guaranteed valid out to MAX_ORDER,
* where that page is in a different zone we will detect
* it from its zone id and abort this block scan.
*/
zone_id = page_zone_id(page);
page_pfn = page_to_pfn(page);
pfn = page_pfn & ~((1 << order) - 1);
end_pfn = pfn + (1 << order);
for (; pfn < end_pfn; pfn++) {
struct page *cursor_page;
/* The target page is in the block, ignore it. */
if (unlikely(pfn == page_pfn))
continue;
/* Avoid holes within the zone. */
if (unlikely(!pfn_valid_within(pfn)))
break;
cursor_page = pfn_to_page(pfn);
/* Check that we have not crossed a zone boundary. */
if (unlikely(page_zone_id(cursor_page) != zone_id))
break;
/*
* If we don't have enough swap space, reclaiming of
* anon page which don't already have a swap slot is
* pointless.
*/
if (nr_swap_pages <= 0 && PageSwapBacked(cursor_page) &&
!PageSwapCache(cursor_page))
break;
if (__isolate_lru_page(cursor_page, mode, file) == 0) {
list_move(&cursor_page->lru, dst);
mem_cgroup_del_lru(cursor_page);
nr_taken += hpage_nr_pages(page);
nr_lumpy_taken++;
if (PageDirty(cursor_page))
nr_lumpy_dirty++;
scan++;
} else {
/*
* Check if the page is freed already.
*
* We can't use page_count() as that
* requires compound_head and we don't
* have a pin on the page here. If a
* page is tail, we may or may not
* have isolated the head, so assume
* it's not free, it'd be tricky to
* track the head status without a
* page pin.
*/
if (!PageTail(cursor_page) &&
!atomic_read(&cursor_page->_count))
continue;
break;
}
}
/* If we break out of the loop above, lumpy reclaim failed */
if (pfn < end_pfn)
nr_lumpy_failed++;
}
*scanned = scan;
trace_mm_vmscan_lru_isolate(order,
nr_to_scan, scan,
nr_taken,
nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed,
mode);
return nr_taken;
}
static unsigned long isolate_pages_global(unsigned long nr,
struct list_head *dst,
unsigned long *scanned, int order,
isolate_mode_t mode,
struct zone *z, int active, int file)
{
int lru = LRU_BASE;
if (active)
lru += LRU_ACTIVE;
if (file)
lru += LRU_FILE;
return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
mode, file);
}
/*
* clear_active_flags() is a helper for shrink_active_list(), clearing
* any active bits from the pages in the list.
*/
static unsigned long clear_active_flags(struct list_head *page_list,
unsigned int *count)
{
int nr_active = 0;
int lru;
struct page *page;
list_for_each_entry(page, page_list, lru) {
int numpages = hpage_nr_pages(page);
lru = page_lru_base_type(page);
if (PageActive(page)) {
lru += LRU_ACTIVE;
ClearPageActive(page);
nr_active += numpages;
}
if (count)
count[lru] += numpages;
}
return nr_active;
}
/**
* isolate_lru_page - tries to isolate a page from its LRU list
* @page: page to isolate from its LRU list
*
* Isolates a @page from an LRU list, clears PageLRU and adjusts the
* vmstat statistic corresponding to whatever LRU list the page was on.
*
* Returns 0 if the page was removed from an LRU list.
* Returns -EBUSY if the page was not on an LRU list.
*
* The returned page will have PageLRU() cleared. If it was found on
* the active list, it will have PageActive set. If it was found on
* the unevictable list, it will have the PageUnevictable bit set. That flag
* may need to be cleared by the caller before letting the page go.
*
* The vmstat statistic corresponding to the list on which the page was
* found will be decremented.
*
* Restrictions:
* (1) Must be called with an elevated refcount on the page. This is a
* fundamentnal difference from isolate_lru_pages (which is called
* without a stable reference).
* (2) the lru_lock must not be held.
* (3) interrupts must be enabled.
*/
int isolate_lru_page(struct page *page)
{
int ret = -EBUSY;
VM_BUG_ON(!page_count(page));
if (PageLRU(page)) {
struct zone *zone = page_zone(page);
spin_lock_irq(&zone->lru_lock);
if (PageLRU(page)) {
int lru = page_lru(page);
ret = 0;
get_page(page);
ClearPageLRU(page);
del_page_from_lru_list(zone, page, lru);
}
spin_unlock_irq(&zone->lru_lock);
}
return ret;
}
/*
* Are there way too many processes in the direct reclaim path already?
*/
static int too_many_isolated(struct zone *zone, int file,
struct scan_control *sc)
{
unsigned long inactive, isolated;
if (current_is_kswapd())
return 0;
if (!scanning_global_lru(sc))
return 0;
if (file) {
inactive = zone_page_state(zone, NR_INACTIVE_FILE);
isolated = zone_page_state(zone, NR_ISOLATED_FILE);
} else {
inactive = zone_page_state(zone, NR_INACTIVE_ANON);
isolated = zone_page_state(zone, NR_ISOLATED_ANON);
}
return isolated > inactive;
}
/*
* TODO: Try merging with migrations version of putback_lru_pages
*/
static noinline_for_stack void
putback_lru_pages(struct zone *zone, struct scan_control *sc,
unsigned long nr_anon, unsigned long nr_file,
struct list_head *page_list)
{
struct page *page;
struct pagevec pvec;
struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
pagevec_init(&pvec, 1);
/*
* Put back any unfreeable pages.
*/
spin_lock(&zone->lru_lock);
while (!list_empty(page_list)) {
int lru;
page = lru_to_page(page_list);
VM_BUG_ON(PageLRU(page));
list_del(&page->lru);
if (unlikely(!page_evictable(page, NULL))) {
spin_unlock_irq(&zone->lru_lock);
putback_lru_page(page);
spin_lock_irq(&zone->lru_lock);
continue;
}
SetPageLRU(page);
lru = page_lru(page);
add_page_to_lru_list(zone, page, lru);
if (is_active_lru(lru)) {
int file = is_file_lru(lru);
int numpages = hpage_nr_pages(page);
reclaim_stat->recent_rotated[file] += numpages;
}
if (!pagevec_add(&pvec, page)) {
spin_unlock_irq(&zone->lru_lock);
__pagevec_release(&pvec);
spin_lock_irq(&zone->lru_lock);
}
}
__mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
__mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
spin_unlock_irq(&zone->lru_lock);
pagevec_release(&pvec);
}
static noinline_for_stack void update_isolated_counts(struct zone *zone,
struct scan_control *sc,
unsigned long *nr_anon,
unsigned long *nr_file,
struct list_head *isolated_list)
{
unsigned long nr_active;
unsigned int count[NR_LRU_LISTS] = { 0, };
struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
nr_active = clear_active_flags(isolated_list, count);
__count_vm_events(PGDEACTIVATE, nr_active);
__mod_zone_page_state(zone, NR_ACTIVE_FILE,
-count[LRU_ACTIVE_FILE]);
__mod_zone_page_state(zone, NR_INACTIVE_FILE,
-count[LRU_INACTIVE_FILE]);
__mod_zone_page_state(zone, NR_ACTIVE_ANON,
-count[LRU_ACTIVE_ANON]);
__mod_zone_page_state(zone, NR_INACTIVE_ANON,
-count[LRU_INACTIVE_ANON]);
*nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
*nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
__mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
__mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
reclaim_stat->recent_scanned[0] += *nr_anon;
reclaim_stat->recent_scanned[1] += *nr_file;
}
/*
* Returns true if the caller should wait to clean dirty/writeback pages.
*
* If we are direct reclaiming for contiguous pages and we do not reclaim
* everything in the list, try again and wait for writeback IO to complete.
* This will stall high-order allocations noticeably. Only do that when really
* need to free the pages under high memory pressure.
*/
static inline bool should_reclaim_stall(unsigned long nr_taken,
unsigned long nr_freed,
int priority,
struct scan_control *sc)
{
int lumpy_stall_priority;
/* kswapd should not stall on sync IO */
if (current_is_kswapd())
return false;
/* Only stall on lumpy reclaim */
if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)
return false;
/* If we have relaimed everything on the isolated list, no stall */
if (nr_freed == nr_taken)
return false;
/*
* For high-order allocations, there are two stall thresholds.
* High-cost allocations stall immediately where as lower
* order allocations such as stacks require the scanning
* priority to be much higher before stalling.
*/
if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
lumpy_stall_priority = DEF_PRIORITY;
else
lumpy_stall_priority = DEF_PRIORITY / 3;
return priority <= lumpy_stall_priority;
}
/*
* shrink_inactive_list() is a helper for shrink_zone(). It returns the number
* of reclaimed pages
*/
static noinline_for_stack unsigned long
shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
struct scan_control *sc, int priority, int file)
{
LIST_HEAD(page_list);
unsigned long nr_scanned;
unsigned long nr_reclaimed = 0;
unsigned long nr_taken;
unsigned long nr_anon;
unsigned long nr_file;
isolate_mode_t reclaim_mode = ISOLATE_INACTIVE;
while (unlikely(too_many_isolated(zone, file, sc))) {
congestion_wait(BLK_RW_ASYNC, HZ/10);
/* We are about to die and free our memory. Return now. */
if (fatal_signal_pending(current))
return SWAP_CLUSTER_MAX;
}
set_reclaim_mode(priority, sc, false);
if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
reclaim_mode |= ISOLATE_ACTIVE;
lru_add_drain();
if (!sc->may_unmap)
reclaim_mode |= ISOLATE_UNMAPPED;
if (!sc->may_writepage)
reclaim_mode |= ISOLATE_CLEAN;
spin_lock_irq(&zone->lru_lock);
if (scanning_global_lru(sc)) {
nr_taken = isolate_pages_global(nr_to_scan, &page_list,
&nr_scanned, sc->order, reclaim_mode, zone, 0, file);
zone->pages_scanned += nr_scanned;
if (current_is_kswapd())
__count_zone_vm_events(PGSCAN_KSWAPD, zone,
nr_scanned);
else
__count_zone_vm_events(PGSCAN_DIRECT, zone,
nr_scanned);
} else {
nr_taken = mem_cgroup_isolate_pages(nr_to_scan, &page_list,
&nr_scanned, sc->order, reclaim_mode, zone,
sc->mem_cgroup, 0, file);
/*
* mem_cgroup_isolate_pages() keeps track of
* scanned pages on its own.
*/
}
if (nr_taken == 0) {
spin_unlock_irq(&zone->lru_lock);
return 0;
}
update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list);
spin_unlock_irq(&zone->lru_lock);
nr_reclaimed = shrink_page_list(&page_list, zone, sc);
/* Check if we should syncronously wait for writeback */
if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
set_reclaim_mode(priority, sc, true);
nr_reclaimed += shrink_page_list(&page_list, zone, sc);
}
local_irq_disable();
if (current_is_kswapd())
__count_vm_events(KSWAPD_STEAL, nr_reclaimed);
__count_zone_vm_events(PGSTEAL, zone, nr_reclaimed);
putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list);
trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
zone_idx(zone),
nr_scanned, nr_reclaimed,
priority,
trace_shrink_flags(file, sc->reclaim_mode));
return nr_reclaimed;
}
/*
* This moves pages from the active list to the inactive list.
*
* We move them the other way if the page is referenced by one or more
* processes, from rmap.
*
* If the pages are mostly unmapped, the processing is fast and it is
* appropriate to hold zone->lru_lock across the whole operation. But if
* the pages are mapped, the processing is slow (page_referenced()) so we
* should drop zone->lru_lock around each page. It's impossible to balance
* this, so instead we remove the pages from the LRU while processing them.
* It is safe to rely on PG_active against the non-LRU pages in here because
* nobody will play with that bit on a non-LRU page.
*
* The downside is that we have to touch page->_count against each page.
* But we had to alter page->flags anyway.
*/
static void move_active_pages_to_lru(struct zone *zone,
struct list_head *list,
enum lru_list lru)
{
unsigned long pgmoved = 0;
struct pagevec pvec;
struct page *page;
pagevec_init(&pvec, 1);
while (!list_empty(list)) {
page = lru_to_page(list);
VM_BUG_ON(PageLRU(page));
SetPageLRU(page);
list_move(&page->lru, &zone->lru[lru].list);
mem_cgroup_add_lru_list(page, lru);
pgmoved += hpage_nr_pages(page);
if (!pagevec_add(&pvec, page) || list_empty(list)) {
spin_unlock_irq(&zone->lru_lock);
if (buffer_heads_over_limit)
pagevec_strip(&pvec);
__pagevec_release(&pvec);
spin_lock_irq(&zone->lru_lock);
}
}
__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
if (!is_active_lru(lru))
__count_vm_events(PGDEACTIVATE, pgmoved);
}
static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
struct scan_control *sc, int priority, int file)
{
unsigned long nr_taken;
unsigned long pgscanned;
unsigned long vm_flags;
LIST_HEAD(l_hold); /* The pages which were snipped off */
LIST_HEAD(l_active);
LIST_HEAD(l_inactive);
struct page *page;
struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
unsigned long nr_rotated = 0;
isolate_mode_t reclaim_mode = ISOLATE_ACTIVE;
lru_add_drain();
if (!sc->may_unmap)
reclaim_mode |= ISOLATE_UNMAPPED;
if (!sc->may_writepage)
reclaim_mode |= ISOLATE_CLEAN;
spin_lock_irq(&zone->lru_lock);
if (scanning_global_lru(sc)) {
nr_taken = isolate_pages_global(nr_pages, &l_hold,
&pgscanned, sc->order,
reclaim_mode, zone,
1, file);
zone->pages_scanned += pgscanned;
} else {
nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
&pgscanned, sc->order,
reclaim_mode, zone,
sc->mem_cgroup, 1, file);
/*
* mem_cgroup_isolate_pages() keeps track of
* scanned pages on its own.
*/
}
reclaim_stat->recent_scanned[file] += nr_taken;
__count_zone_vm_events(PGREFILL, zone, pgscanned);
if (file)
__mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
else
__mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
spin_unlock_irq(&zone->lru_lock);
while (!list_empty(&l_hold)) {
cond_resched();
page = lru_to_page(&l_hold);
list_del(&page->lru);
if (unlikely(!page_evictable(page, NULL))) {
putback_lru_page(page);
continue;
}
if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
nr_rotated += hpage_nr_pages(page);
/*
* Identify referenced, file-backed active pages and
* give them one more trip around the active list. So
* that executable code get better chances to stay in
* memory under moderate memory pressure. Anon pages
* are not likely to be evicted by use-once streaming
* IO, plus JVM can create lots of anon VM_EXEC pages,
* so we ignore them here.
*/
if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
list_add(&page->lru, &l_active);
continue;
}
}
ClearPageActive(page); /* we are de-activating */
list_add(&page->lru, &l_inactive);
}
/*
* Move pages back to the lru list.
*/
spin_lock_irq(&zone->lru_lock);
/*
* Count referenced pages from currently used mappings as rotated,
* even though only some of them are actually re-activated. This
* helps balance scan pressure between file and anonymous pages in
* get_scan_ratio.
*/
reclaim_stat->recent_rotated[file] += nr_rotated;
move_active_pages_to_lru(zone, &l_active,
LRU_ACTIVE + file * LRU_FILE);
move_active_pages_to_lru(zone, &l_inactive,
LRU_BASE + file * LRU_FILE);
__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
spin_unlock_irq(&zone->lru_lock);
}
#ifdef CONFIG_SWAP
static int inactive_anon_is_low_global(struct zone *zone)
{
unsigned long active, inactive;
active = zone_page_state(zone, NR_ACTIVE_ANON);
inactive = zone_page_state(zone, NR_INACTIVE_ANON);
if (inactive * zone->inactive_ratio < active)
return 1;
return 0;
}
/**
* inactive_anon_is_low - check if anonymous pages need to be deactivated
* @zone: zone to check
* @sc: scan control of this context
*
* Returns true if the zone does not have enough inactive anon pages,
* meaning some active anon pages need to be deactivated.
*/
static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
{
int low;
/*
* If we don't have swap space, anonymous page deactivation
* is pointless.
*/
if (!total_swap_pages)
return 0;
if (scanning_global_lru(sc))
low = inactive_anon_is_low_global(zone);
else
low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
return low;
}
#else
static inline int inactive_anon_is_low(struct zone *zone,
struct scan_control *sc)
{
return 0;
}
#endif
static int inactive_file_is_low_global(struct zone *zone)
{
unsigned long active, inactive;
active = zone_page_state(zone, NR_ACTIVE_FILE);
inactive = zone_page_state(zone, NR_INACTIVE_FILE);
return (active > inactive);
}
/**
* inactive_file_is_low - check if file pages need to be deactivated
* @zone: zone to check
* @sc: scan control of this context
*
* When the system is doing streaming IO, memory pressure here
* ensures that active file pages get deactivated, until more
* than half of the file pages are on the inactive list.
*
* Once we get to that situation, protect the system's working
* set from being evicted by disabling active file page aging.
*
* This uses a different ratio than the anonymous pages, because
* the page cache uses a use-once replacement algorithm.
*/
static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
{
int low;
if (scanning_global_lru(sc))
low = inactive_file_is_low_global(zone);
else
low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
return low;
}
static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
int file)
{
if (file)
return inactive_file_is_low(zone, sc);
else
return inactive_anon_is_low(zone, sc);
}
static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
struct zone *zone, struct scan_control *sc, int priority)
{
int file = is_file_lru(lru);
if (is_active_lru(lru)) {
if (inactive_list_is_low(zone, sc, file))
shrink_active_list(nr_to_scan, zone, sc, priority, file);
return 0;
}
return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
}
/*
* Determine how aggressively the anon and file LRU lists should be
* scanned. The relative value of each set of LRU lists is determined
* by looking at the fraction of the pages scanned we did rotate back
* onto the active list instead of evict.
*
* nr[0] = anon pages to scan; nr[1] = file pages to scan
*/
static void get_scan_count(struct zone *zone, struct scan_control *sc,
unsigned long *nr, int priority)
{
unsigned long anon, file, free;
unsigned long anon_prio, file_prio;
unsigned long ap, fp;
struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
u64 fraction[2], denominator;
enum lru_list l;
int noswap = 0;
bool force_scan = false;
unsigned long nr_force_scan[2];
/* kswapd does zone balancing and needs to scan this zone */
if (scanning_global_lru(sc) && current_is_kswapd() &&
zone->all_unreclaimable)
force_scan = true;
/* memcg may have small limit and need to avoid priority drop */
if (!scanning_global_lru(sc))
force_scan = true;
/* If we have no swap space, do not bother scanning anon pages. */
if (!sc->may_swap || (nr_swap_pages <= 0)) {
noswap = 1;
fraction[0] = 0;
fraction[1] = 1;
denominator = 1;
nr_force_scan[0] = 0;
nr_force_scan[1] = SWAP_CLUSTER_MAX;
goto out;
}
anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
if (scanning_global_lru(sc)) {
free = zone_page_state(zone, NR_FREE_PAGES);
/* If we have very few page cache pages,
force-scan anon pages. */
if (unlikely(file + free <= high_wmark_pages(zone))) {
fraction[0] = 1;
fraction[1] = 0;
denominator = 1;
nr_force_scan[0] = SWAP_CLUSTER_MAX;
nr_force_scan[1] = 0;
goto out;
}
}
/*
* With swappiness at 100, anonymous and file have the same priority.
* This scanning priority is essentially the inverse of IO cost.
*/
anon_prio = sc->swappiness;
file_prio = 200 - sc->swappiness;
/*
* OK, so we have swap space and a fair amount of page cache
* pages. We use the recently rotated / recently scanned
* ratios to determine how valuable each cache is.
*
* Because workloads change over time (and to avoid overflow)
* we keep these statistics as a floating average, which ends
* up weighing recent references more than old ones.
*
* anon in [0], file in [1]
*/
spin_lock_irq(&zone->lru_lock);
if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
reclaim_stat->recent_scanned[0] /= 2;
reclaim_stat->recent_rotated[0] /= 2;
}
if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
reclaim_stat->recent_scanned[1] /= 2;
reclaim_stat->recent_rotated[1] /= 2;
}
/*
* The amount of pressure on anon vs file pages is inversely
* proportional to the fraction of recently scanned pages on
* each list that were recently referenced and in active use.
*/
ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
ap /= reclaim_stat->recent_rotated[0] + 1;
fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
fp /= reclaim_stat->recent_rotated[1] + 1;
spin_unlock_irq(&zone->lru_lock);
fraction[0] = ap;
fraction[1] = fp;
denominator = ap + fp + 1;
if (force_scan) {
unsigned long scan = SWAP_CLUSTER_MAX;
nr_force_scan[0] = div64_u64(scan * ap, denominator);
nr_force_scan[1] = div64_u64(scan * fp, denominator);
}
out:
for_each_evictable_lru(l) {
int file = is_file_lru(l);
unsigned long scan;
scan = zone_nr_lru_pages(zone, sc, l);
if (priority || noswap) {
scan >>= priority;
scan = div64_u64(scan * fraction[file], denominator);
}
/*
* If zone is small or memcg is small, nr[l] can be 0.
* This results no-scan on this priority and priority drop down.
* For global direct reclaim, it can visit next zone and tend
* not to have problems. For global kswapd, it's for zone
* balancing and it need to scan a small amounts. When using
* memcg, priority drop can cause big latency. So, it's better
* to scan small amount. See may_noscan above.
*/
if (!scan && force_scan)
scan = nr_force_scan[file];
nr[l] = scan;
}
}
/*
* Reclaim/compaction depends on a number of pages being freed. To avoid
* disruption to the system, a small number of order-0 pages continue to be
* rotated and reclaimed in the normal fashion. However, by the time we get
* back to the allocator and call try_to_compact_zone(), we ensure that
* there are enough free pages for it to be likely successful
*/
static inline bool should_continue_reclaim(struct zone *zone,
unsigned long nr_reclaimed,
unsigned long nr_scanned,
struct scan_control *sc)
{
unsigned long pages_for_compaction;
unsigned long inactive_lru_pages;
/* If not in reclaim/compaction mode, stop */
if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION))
return false;
/* Consider stopping depending on scan and reclaim activity */
if (sc->gfp_mask & __GFP_REPEAT) {
/*
* For __GFP_REPEAT allocations, stop reclaiming if the
* full LRU list has been scanned and we are still failing
* to reclaim pages. This full LRU scan is potentially
* expensive but a __GFP_REPEAT caller really wants to succeed
*/
if (!nr_reclaimed && !nr_scanned)
return false;
} else {
/*
* For non-__GFP_REPEAT allocations which can presumably
* fail without consequence, stop if we failed to reclaim
* any pages from the last SWAP_CLUSTER_MAX number of
* pages that were scanned. This will return to the
* caller faster at the risk reclaim/compaction and
* the resulting allocation attempt fails
*/
if (!nr_reclaimed)
return false;
}
/*
* If we have not reclaimed enough pages for compaction and the
* inactive lists are large enough, continue reclaiming
*/
pages_for_compaction = (2UL << sc->order);
inactive_lru_pages = zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
if (nr_swap_pages > 0)
inactive_lru_pages += zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
if (sc->nr_reclaimed < pages_for_compaction &&
inactive_lru_pages > pages_for_compaction)
return true;
/* If compaction would go ahead or the allocation would succeed, stop */
switch (compaction_suitable(zone, sc->order)) {
case COMPACT_PARTIAL:
case COMPACT_CONTINUE:
return false;
default:
return true;
}
}
/*
* This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
*/
static void shrink_zone(int priority, struct zone *zone,
struct scan_control *sc)
{
unsigned long nr[NR_LRU_LISTS];
unsigned long nr_to_scan;
enum lru_list l;
unsigned long nr_reclaimed, nr_scanned;
unsigned long nr_to_reclaim = sc->nr_to_reclaim;
restart:
nr_reclaimed = 0;
nr_scanned = sc->nr_scanned;
get_scan_count(zone, sc, nr, priority);
while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
nr[LRU_INACTIVE_FILE]) {
for_each_evictable_lru(l) {
if (nr[l]) {
nr_to_scan = min_t(unsigned long,
nr[l], SWAP_CLUSTER_MAX);
nr[l] -= nr_to_scan;
nr_reclaimed += shrink_list(l, nr_to_scan,
zone, sc, priority);
}
}
/*
* On large memory systems, scan >> priority can become
* really large. This is fine for the starting priority;
* we want to put equal scanning pressure on each zone.
* However, if the VM has a harder time of freeing pages,
* with multiple processes reclaiming pages, the total
* freeing target can get unreasonably large.
*/
if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
break;
}
sc->nr_reclaimed += nr_reclaimed;
/*
* Even if we did not try to evict anon pages at all, we want to
* rebalance the anon lru active/inactive ratio.
*/
if (inactive_anon_is_low(zone, sc))
shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
/* reclaim/compaction might need reclaim to continue */
if (should_continue_reclaim(zone, nr_reclaimed,
sc->nr_scanned - nr_scanned, sc))
goto restart;
throttle_vm_writeout(sc->gfp_mask);
}
/* Returns true if compaction should go ahead for a high-order request */
static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
{
unsigned long balance_gap, watermark;
bool watermark_ok;
/* Do not consider compaction for orders reclaim is meant to satisfy */
if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
return false;
/*
* Compaction takes time to run and there are potentially other
* callers using the pages just freed. Continue reclaiming until
* there is a buffer of free pages available to give compaction
* a reasonable chance of completing and allocating the page
*/
balance_gap = min(low_wmark_pages(zone),
(zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
KSWAPD_ZONE_BALANCE_GAP_RATIO);
watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
/*
* If compaction is deferred, reclaim up to a point where
* compaction will have a chance of success when re-enabled
*/
if (compaction_deferred(zone))
return watermark_ok;
/* If compaction is not ready to start, keep reclaiming */
if (!compaction_suitable(zone, sc->order))
return false;
return watermark_ok;
}
/*
* This is the direct reclaim path, for page-allocating processes. We only
* try to reclaim pages from zones which will satisfy the caller's allocation
* request.
*
* We reclaim from a zone even if that zone is over high_wmark_pages(zone).
* Because:
* a) The caller may be trying to free *extra* pages to satisfy a higher-order
* allocation or
* b) The target zone may be at high_wmark_pages(zone) but the lower zones
* must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
* zone defense algorithm.
*
* If a zone is deemed to be full of pinned pages then just give it a light
* scan then give up on it.
*
* This function returns true if a zone is being reclaimed for a costly
* high-order allocation and compaction is ready to begin. This indicates to
* the caller that it should consider retrying the allocation instead of
* further reclaim.
*/
static bool shrink_zones(int priority, struct zonelist *zonelist,
struct scan_control *sc)
{
struct zoneref *z;
struct zone *zone;
unsigned long nr_soft_reclaimed;
unsigned long nr_soft_scanned;
bool aborted_reclaim = false;
for_each_zone_zonelist_nodemask(zone, z, zonelist,
gfp_zone(sc->gfp_mask), sc->nodemask) {
if (!populated_zone(zone))
continue;
/*
* Take care memory controller reclaiming has small influence
* to global LRU.
*/
if (scanning_global_lru(sc)) {
if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
continue;
if (zone->all_unreclaimable && priority != DEF_PRIORITY)
continue; /* Let kswapd poll it */
if (COMPACTION_BUILD) {
/*
* If we already have plenty of memory free for
* compaction in this zone, don't free any more.
* Even though compaction is invoked for any
* non-zero order, only frequent costly order
* reclamation is disruptive enough to become a
* noticable problem, like transparent huge page
* allocations.
*/
if (compaction_ready(zone, sc)) {
aborted_reclaim = true;
continue;
}
}
/*
* This steals pages from memory cgroups over softlimit
* and returns the number of reclaimed pages and
* scanned pages. This works for global memory pressure
* and balancing, not for a memcg's limit.
*/
nr_soft_scanned = 0;
nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
sc->order, sc->gfp_mask,
&nr_soft_scanned);
sc->nr_reclaimed += nr_soft_reclaimed;
sc->nr_scanned += nr_soft_scanned;
/* need some check for avoid more shrink_zone() */
}
shrink_zone(priority, zone, sc);
}
return aborted_reclaim;
}
static bool zone_reclaimable(struct zone *zone)
{
return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
}
/* All zones in zonelist are unreclaimable? */
static bool all_unreclaimable(struct zonelist *zonelist,
struct scan_control *sc)
{
struct zoneref *z;
struct zone *zone;
for_each_zone_zonelist_nodemask(zone, z, zonelist,
gfp_zone(sc->gfp_mask), sc->nodemask) {
if (!populated_zone(zone))
continue;
if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
continue;
if (!zone->all_unreclaimable)
return false;
}
return true;
}
/*
* This is the main entry point to direct page reclaim.
*
* If a full scan of the inactive list fails to free enough memory then we
* are "out of memory" and something needs to be killed.
*
* If the caller is !__GFP_FS then the probability of a failure is reasonably
* high - the zone may be full of dirty or under-writeback pages, which this
* caller can't do much about. We kick the writeback threads and take explicit
* naps in the hope that some of these pages can be written. But if the
* allocating task holds filesystem locks which prevent writeout this might not
* work, and the allocation attempt will fail.
*
* returns: 0, if no pages reclaimed
* else, the number of pages reclaimed
*/
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
struct scan_control *sc,
struct shrink_control *shrink)
{
int priority;
unsigned long total_scanned = 0;
struct reclaim_state *reclaim_state = current->reclaim_state;
struct zoneref *z;
struct zone *zone;
unsigned long writeback_threshold;
bool aborted_reclaim;
delayacct_freepages_start();
if (scanning_global_lru(sc))
count_vm_event(ALLOCSTALL);
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
sc->nr_scanned = 0;
if (!priority)
disable_swap_token(sc->mem_cgroup);
aborted_reclaim = shrink_zones(priority, zonelist, sc);
/*
* Don't shrink slabs when reclaiming memory from
* over limit cgroups
*/
if (scanning_global_lru(sc)) {
unsigned long lru_pages = 0;
for_each_zone_zonelist(zone, z, zonelist,
gfp_zone(sc->gfp_mask)) {
if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
continue;
lru_pages += zone_reclaimable_pages(zone);
}
shrink_slab(shrink, sc->nr_scanned, lru_pages);
if (reclaim_state) {
sc->nr_reclaimed += reclaim_state->reclaimed_slab;
reclaim_state->reclaimed_slab = 0;
}
}
total_scanned += sc->nr_scanned;
if (sc->nr_reclaimed >= sc->nr_to_reclaim)
goto out;
/*
* Try to write back as many pages as we just scanned. This
* tends to cause slow streaming writers to write data to the
* disk smoothly, at the dirtying rate, which is nice. But
* that's undesirable in laptop mode, where we *want* lumpy
* writeout. So in laptop mode, write out the whole world.
*/
writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
if (total_scanned > writeback_threshold) {
wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
sc->may_writepage = 1;
}
/* Take a nap, wait for some writeback to complete */
if (!sc->hibernation_mode && sc->nr_scanned &&
priority < DEF_PRIORITY - 2) {
struct zone *preferred_zone;
first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
&cpuset_current_mems_allowed,
&preferred_zone);
wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
}
}
out:
delayacct_freepages_end();
if (sc->nr_reclaimed)
return sc->nr_reclaimed;
/*
* As hibernation is going on, kswapd is freezed so that it can't mark
* the zone into all_unreclaimable. Thus bypassing all_unreclaimable
* check.
*/
if (oom_killer_disabled)
return 0;
/* Aborted reclaim to try compaction? don't OOM, then */
if (aborted_reclaim)
return 1;
/* top priority shrink_zones still had more to do? don't OOM, then */
if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
return 1;
return 0;
}
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
gfp_t gfp_mask, nodemask_t *nodemask)
{
unsigned long nr_reclaimed;
struct scan_control sc = {
.gfp_mask = gfp_mask,
.may_writepage = !laptop_mode,
.nr_to_reclaim = SWAP_CLUSTER_MAX,
.may_unmap = 1,
.may_swap = 1,
.swappiness = vm_swappiness,
.order = order,
.mem_cgroup = NULL,
.nodemask = nodemask,
};
struct shrink_control shrink = {
.gfp_mask = sc.gfp_mask,
};
trace_mm_vmscan_direct_reclaim_begin(order,
sc.may_writepage,
gfp_mask);
nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
return nr_reclaimed;
}
#ifdef CONFIG_CGROUP_MEM_RES_CTLR
unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
gfp_t gfp_mask, bool noswap,
unsigned int swappiness,
struct zone *zone,
unsigned long *nr_scanned)
{
struct scan_control sc = {
.nr_scanned = 0,
.nr_to_reclaim = SWAP_CLUSTER_MAX,
.may_writepage = !laptop_mode,
.may_unmap = 1,
.may_swap = !noswap,
.swappiness = swappiness,
.order = 0,
.mem_cgroup = mem,
};
sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
trace_mm_vmscan_memcg_softlimit_reclaim_begin(0,
sc.may_writepage,
sc.gfp_mask);
/*
* NOTE: Although we can get the priority field, using it
* here is not a good idea, since it limits the pages we can scan.
* if we don't reclaim here, the shrink_zone from balance_pgdat
* will pick up pages from other mem cgroup's as well. We hack
* the priority and make it zero.
*/
shrink_zone(0, zone, &sc);
trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
*nr_scanned = sc.nr_scanned;
return sc.nr_reclaimed;
}
unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
gfp_t gfp_mask,
bool noswap,
unsigned int swappiness)
{
struct zonelist *zonelist;
unsigned long nr_reclaimed;
int nid;
struct scan_control sc = {
.may_writepage = !laptop_mode,
.may_unmap = 1,
.may_swap = !noswap,
.nr_to_reclaim = SWAP_CLUSTER_MAX,
.swappiness = swappiness,
.order = 0,
.mem_cgroup = mem_cont,
.nodemask = NULL, /* we don't care the placement */
.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
};
struct shrink_control shrink = {
.gfp_mask = sc.gfp_mask,
};
/*
* Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
* take care of from where we get pages. So the node where we start the
* scan does not need to be the current node.
*/
nid = mem_cgroup_select_victim_node(mem_cont);
zonelist = NODE_DATA(nid)->node_zonelists;
trace_mm_vmscan_memcg_reclaim_begin(0,
sc.may_writepage,
sc.gfp_mask);
nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
return nr_reclaimed;
}
#endif
/*
* pgdat_balanced is used when checking if a node is balanced for high-order
* allocations. Only zones that meet watermarks and are in a zone allowed
* by the callers classzone_idx are added to balanced_pages. The total of
* balanced pages must be at least 25% of the zones allowed by classzone_idx
* for the node to be considered balanced. Forcing all zones to be balanced
* for high orders can cause excessive reclaim when there are imbalanced zones.
* The choice of 25% is due to
* o a 16M DMA zone that is balanced will not balance a zone on any
* reasonable sized machine
* o On all other machines, the top zone must be at least a reasonable
* percentage of the middle zones. For example, on 32-bit x86, highmem
* would need to be at least 256M for it to be balance a whole node.
* Similarly, on x86-64 the Normal zone would need to be at least 1G
* to balance a node on its own. These seemed like reasonable ratios.
*/
static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
int classzone_idx)
{
unsigned long present_pages = 0;
int i;
for (i = 0; i <= classzone_idx; i++)
present_pages += pgdat->node_zones[i].present_pages;
/* A special case here: if zone has no page, we think it's balanced */
return balanced_pages >= (present_pages >> 2);
}
/* is kswapd sleeping prematurely? */
static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
int classzone_idx)
{
int i;
unsigned long balanced = 0;
bool all_zones_ok = true;
/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
if (remaining)
return true;
/* Check the watermark levels */
for (i = 0; i <= classzone_idx; i++) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
/*
* balance_pgdat() skips over all_unreclaimable after
* DEF_PRIORITY. Effectively, it considers them balanced so
* they must be considered balanced here as well if kswapd
* is to sleep
*/
if (zone->all_unreclaimable) {
balanced += zone->present_pages;
continue;
}
if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
i, 0))
all_zones_ok = false;
else
balanced += zone->present_pages;
}
/*
* For high-order requests, the balanced zones must contain at least
* 25% of the nodes pages for kswapd to sleep. For order-0, all zones
* must be balanced
*/
if (order)
return !pgdat_balanced(pgdat, balanced, classzone_idx);
else
return !all_zones_ok;
}
/*
* For kswapd, balance_pgdat() will work across all this node's zones until
* they are all at high_wmark_pages(zone).
*
* Returns the final order kswapd was reclaiming at
*
* There is special handling here for zones which are full of pinned pages.
* This can happen if the pages are all mlocked, or if they are all used by
* device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
* What we do is to detect the case where all pages in the zone have been
* scanned twice and there has been zero successful reclaim. Mark the zone as
* dead and from now on, only perform a short scan. Basically we're polling
* the zone for when the problem goes away.
*
* kswapd scans the zones in the highmem->normal->dma direction. It skips
* zones which have free_pages > high_wmark_pages(zone), but once a zone is
* found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
* lower zones regardless of the number of free pages in the lower zones. This
* interoperates with the page allocator fallback scheme to ensure that aging
* of pages is balanced across the zones.
*/
static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
int *classzone_idx)
{
int all_zones_ok;
unsigned long balanced;
int priority;
int i;
int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long total_scanned;
struct reclaim_state *reclaim_state = current->reclaim_state;
unsigned long nr_soft_reclaimed;
unsigned long nr_soft_scanned;
struct scan_control sc = {
.gfp_mask = GFP_KERNEL,
.may_unmap = 1,
.may_swap = 1,
/*
* kswapd doesn't want to be bailed out while reclaim. because
* we want to put equal scanning pressure on each zone.
*/
.nr_to_reclaim = ULONG_MAX,
.swappiness = vm_swappiness,
.order = order,
.mem_cgroup = NULL,
};
struct shrink_control shrink = {
.gfp_mask = sc.gfp_mask,
};
loop_again:
total_scanned = 0;
sc.nr_reclaimed = 0;
sc.may_writepage = !laptop_mode;
count_vm_event(PAGEOUTRUN);
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
unsigned long lru_pages = 0;
int has_under_min_watermark_zone = 0;
/* The swap token gets in the way of swapout... */
if (!priority)
disable_swap_token(NULL);
all_zones_ok = 1;
balanced = 0;
/*
* Scan in the highmem->dma direction for the highest
* zone which needs scanning
*/
for (i = pgdat->nr_zones - 1; i >= 0; i--) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (zone->all_unreclaimable && priority != DEF_PRIORITY)
continue;
/*
* Do some background aging of the anon list, to give
* pages a chance to be referenced before reclaiming.
*/
if (inactive_anon_is_low(zone, &sc))
shrink_active_list(SWAP_CLUSTER_MAX, zone,
&sc, priority, 0);
if (!zone_watermark_ok_safe(zone, order,
high_wmark_pages(zone), 0, 0)) {
end_zone = i;
break;
} else {
/* If balanced, clear the congested flag */
zone_clear_flag(zone, ZONE_CONGESTED);
}
}
if (i < 0)
goto out;
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
lru_pages += zone_reclaimable_pages(zone);
}
/*
* Now scan the zone in the dma->highmem direction, stopping
* at the last zone which needs scanning.
*
* We do this because the page allocator works in the opposite
* direction. This prevents the page allocator from allocating
* pages behind kswapd's direction of progress, which would
* cause too much scanning of the lower zones.
*/
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
int nr_slab;
unsigned long balance_gap;
if (!populated_zone(zone))
continue;
if (zone->all_unreclaimable && priority != DEF_PRIORITY)
continue;
sc.nr_scanned = 0;
nr_soft_scanned = 0;
/*
* Call soft limit reclaim before calling shrink_zone.
*/
nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
order, sc.gfp_mask,
&nr_soft_scanned);
sc.nr_reclaimed += nr_soft_reclaimed;
total_scanned += nr_soft_scanned;
/*
* We put equal pressure on every zone, unless
* one zone has way too many pages free
* already. The "too many pages" is defined
* as the high wmark plus a "gap" where the
* gap is either the low watermark or 1%
* of the zone, whichever is smaller.
*/
balance_gap = min(low_wmark_pages(zone),
(zone->present_pages +
KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
KSWAPD_ZONE_BALANCE_GAP_RATIO);
if (!zone_watermark_ok_safe(zone, order,
high_wmark_pages(zone) + balance_gap,
end_zone, 0)) {
shrink_zone(priority, zone, &sc);
reclaim_state->reclaimed_slab = 0;
nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
sc.nr_reclaimed += reclaim_state->reclaimed_slab;
total_scanned += sc.nr_scanned;
if (nr_slab == 0 && !zone_reclaimable(zone))
zone->all_unreclaimable = 1;
}
/*
* If we've done a decent amount of scanning and
* the reclaim ratio is low, start doing writepage
* even in laptop mode
*/
if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
sc.may_writepage = 1;
if (zone->all_unreclaimable) {
if (end_zone && end_zone == i)
end_zone--;
continue;
}
if (!zone_watermark_ok_safe(zone, order,
high_wmark_pages(zone), end_zone, 0)) {
all_zones_ok = 0;
/*
* We are still under min water mark. This
* means that we have a GFP_ATOMIC allocation
* failure risk. Hurry up!
*/
if (!zone_watermark_ok_safe(zone, order,
min_wmark_pages(zone), end_zone, 0))
has_under_min_watermark_zone = 1;
} else {
/*
* If a zone reaches its high watermark,
* consider it to be no longer congested. It's
* possible there are dirty pages backed by
* congested BDIs but as pressure is relieved,
* spectulatively avoid congestion waits
*/
zone_clear_flag(zone, ZONE_CONGESTED);
if (i <= *classzone_idx)
balanced += zone->present_pages;
}
}
if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
break; /* kswapd: all done */
/*
* OK, kswapd is getting into trouble. Take a nap, then take
* another pass across the zones.
*/
if (total_scanned && (priority < DEF_PRIORITY - 2)) {
if (has_under_min_watermark_zone)
count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
else
congestion_wait(BLK_RW_ASYNC, HZ/10);
}
/*
* We do this so kswapd doesn't build up large priorities for
* example when it is freeing in parallel with allocators. It
* matches the direct reclaim path behaviour in terms of impact
* on zone->*_priority.
*/
if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
break;
}
out:
/*
* order-0: All zones must meet high watermark for a balanced node
* high-order: Balanced zones must make up at least 25% of the node
* for the node to be balanced
*/
if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
cond_resched();
try_to_freeze();
/*
* Fragmentation may mean that the system cannot be
* rebalanced for high-order allocations in all zones.
* At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
* it means the zones have been fully scanned and are still
* not balanced. For high-order allocations, there is
* little point trying all over again as kswapd may
* infinite loop.
*
* Instead, recheck all watermarks at order-0 as they
* are the most important. If watermarks are ok, kswapd will go
* back to sleep. High-order users can still perform direct
* reclaim if they wish.
*/
if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
order = sc.order = 0;
goto loop_again;
}
/*
* If kswapd was reclaiming at a higher order, it has the option of
* sleeping without all zones being balanced. Before it does, it must
* ensure that the watermarks for order-0 on *all* zones are met and
* that the congestion flags are cleared. The congestion flag must
* be cleared as kswapd is the only mechanism that clears the flag
* and it is potentially going to sleep here.
*/
if (order) {
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (zone->all_unreclaimable && priority != DEF_PRIORITY)
continue;
/* Confirm the zone is balanced for order-0 */
if (!zone_watermark_ok(zone, 0,
high_wmark_pages(zone), 0, 0)) {
order = sc.order = 0;
goto loop_again;
}
/* If balanced, clear the congested flag */
zone_clear_flag(zone, ZONE_CONGESTED);
}
}
/*
* Return the order we were reclaiming at so sleeping_prematurely()
* makes a decision on the order we were last reclaiming at. However,
* if another caller entered the allocator slow path while kswapd
* was awake, order will remain at the higher level
*/
*classzone_idx = end_zone;
return order;
}
static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
{
long remaining = 0;
DEFINE_WAIT(wait);
if (freezing(current) || kthread_should_stop())
return;
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
/* Try to sleep for a short interval */
if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
remaining = schedule_timeout(HZ/10);
finish_wait(&pgdat->kswapd_wait, &wait);
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
}
/*
* After a short sleep, check if it was a premature sleep. If not, then
* go fully to sleep until explicitly woken up.
*/
if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
/*
* vmstat counters are not perfectly accurate and the estimated
* value for counters such as NR_FREE_PAGES can deviate from the
* true value by nr_online_cpus * threshold. To avoid the zone
* watermarks being breached while under pressure, we reduce the
* per-cpu vmstat threshold while kswapd is awake and restore
* them before going back to sleep.
*/
set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
if (!kthread_should_stop())
schedule();
set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
} else {
if (remaining)
count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
else
count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
}
finish_wait(&pgdat->kswapd_wait, &wait);
}
/*
* The background pageout daemon, started as a kernel thread
* from the init process.
*
* This basically trickles out pages so that we have _some_
* free memory available even if there is no other activity
* that frees anything up. This is needed for things like routing
* etc, where we otherwise might have all activity going on in
* asynchronous contexts that cannot page things out.
*
* If there are applications that are active memory-allocators
* (most normal use), this basically shouldn't matter.
*/
static int kswapd(void *p)
{
unsigned long order, new_order;
unsigned balanced_order;
int classzone_idx, new_classzone_idx;
int balanced_classzone_idx;
pg_data_t *pgdat = (pg_data_t*)p;
struct task_struct *tsk = current;
struct reclaim_state reclaim_state = {
.reclaimed_slab = 0,
};
const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
lockdep_set_current_reclaim_state(GFP_KERNEL);
if (!cpumask_empty(cpumask))
set_cpus_allowed_ptr(tsk, cpumask);
current->reclaim_state = &reclaim_state;
/*
* Tell the memory management that we're a "memory allocator",
* and that if we need more memory we should get access to it
* regardless (see "__alloc_pages()"). "kswapd" should
* never get caught in the normal page freeing logic.
*
* (Kswapd normally doesn't need memory anyway, but sometimes
* you need a small amount of memory in order to be able to
* page out something else, and this flag essentially protects
* us from recursively trying to free more memory as we're
* trying to free the first piece of memory in the first place).
*/
tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
set_freezable();
order = new_order = 0;
balanced_order = 0;
classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
balanced_classzone_idx = classzone_idx;
for ( ; ; ) {
int ret;
/*
* If the last balance_pgdat was unsuccessful it's unlikely a
* new request of a similar or harder type will succeed soon
* so consider going to sleep on the basis we reclaimed at
*/
if (balanced_classzone_idx >= new_classzone_idx &&
balanced_order == new_order) {
new_order = pgdat->kswapd_max_order;
new_classzone_idx = pgdat->classzone_idx;
pgdat->kswapd_max_order = 0;
pgdat->classzone_idx = pgdat->nr_zones - 1;
}
if (order < new_order || classzone_idx > new_classzone_idx) {
/*
* Don't sleep if someone wants a larger 'order'
* allocation or has tigher zone constraints
*/
order = new_order;
classzone_idx = new_classzone_idx;
} else {
kswapd_try_to_sleep(pgdat, balanced_order,
balanced_classzone_idx);
order = pgdat->kswapd_max_order;
classzone_idx = pgdat->classzone_idx;
new_order = order;
new_classzone_idx = classzone_idx;
pgdat->kswapd_max_order = 0;
pgdat->classzone_idx = pgdat->nr_zones - 1;
}
ret = try_to_freeze();
if (kthread_should_stop())
break;
/*
* We can speed up thawing tasks if we don't call balance_pgdat
* after returning from the refrigerator
*/
if (!ret) {
trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
balanced_classzone_idx = classzone_idx;
balanced_order = balance_pgdat(pgdat, order,
&balanced_classzone_idx);
}
}
current->reclaim_state = NULL;
return 0;
}
/*
* A zone is low on free memory, so wake its kswapd task to service it.
*/
void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
{
pg_data_t *pgdat;
if (!populated_zone(zone))
return;
if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
return;
pgdat = zone->zone_pgdat;
if (pgdat->kswapd_max_order < order) {
pgdat->kswapd_max_order = order;
pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
}
if (!waitqueue_active(&pgdat->kswapd_wait))
return;
if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
return;
trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
wake_up_interruptible(&pgdat->kswapd_wait);
}
/*
* The reclaimable count would be mostly accurate.
* The less reclaimable pages may be
* - mlocked pages, which will be moved to unevictable list when encountered
* - mapped pages, which may require several travels to be reclaimed
* - dirty pages, which is not "instantly" reclaimable
*/
unsigned long global_reclaimable_pages(void)
{
int nr;
nr = global_page_state(NR_ACTIVE_FILE) +
global_page_state(NR_INACTIVE_FILE);
if (nr_swap_pages > 0)
nr += global_page_state(NR_ACTIVE_ANON) +
global_page_state(NR_INACTIVE_ANON);
return nr;
}
unsigned long zone_reclaimable_pages(struct zone *zone)
{
int nr;
nr = zone_page_state(zone, NR_ACTIVE_FILE) +
zone_page_state(zone, NR_INACTIVE_FILE);
if (nr_swap_pages > 0)
nr += zone_page_state(zone, NR_ACTIVE_ANON) +
zone_page_state(zone, NR_INACTIVE_ANON);
return nr;
}
#ifdef CONFIG_HIBERNATION
/*
* Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
* freed pages.
*
* Rather than trying to age LRUs the aim is to preserve the overall
* LRU order by reclaiming preferentially
* inactive > active > active referenced > active mapped
*/
unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
{
struct reclaim_state reclaim_state;
struct scan_control sc = {
.gfp_mask = GFP_HIGHUSER_MOVABLE,
.may_swap = 1,
.may_unmap = 1,
.may_writepage = 1,
.nr_to_reclaim = nr_to_reclaim,
.hibernation_mode = 1,
.swappiness = vm_swappiness,
.order = 0,
};
struct shrink_control shrink = {
.gfp_mask = sc.gfp_mask,
};
struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
struct task_struct *p = current;
unsigned long nr_reclaimed;
p->flags |= PF_MEMALLOC;
lockdep_set_current_reclaim_state(sc.gfp_mask);
reclaim_state.reclaimed_slab = 0;
p->reclaim_state = &reclaim_state;
nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
p->reclaim_state = NULL;
lockdep_clear_current_reclaim_state();
p->flags &= ~PF_MEMALLOC;
return nr_reclaimed;
}
#endif /* CONFIG_HIBERNATION */
/* It's optimal to keep kswapds on the same CPUs as their memory, but
not required for correctness. So if the last cpu in a node goes
away, we get changed to run anywhere: as the first one comes back,
restore their cpu bindings. */
static int __devinit cpu_callback(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
int nid;
if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
for_each_node_state(nid, N_HIGH_MEMORY) {
pg_data_t *pgdat = NODE_DATA(nid);
const struct cpumask *mask;
mask = cpumask_of_node(pgdat->node_id);
if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
/* One of our CPUs online: restore mask */
set_cpus_allowed_ptr(pgdat->kswapd, mask);
}
}
return NOTIFY_OK;
}
/*
* This kswapd start function will be called by init and node-hot-add.
* On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
*/
int kswapd_run(int nid)
{
pg_data_t *pgdat = NODE_DATA(nid);
int ret = 0;
if (pgdat->kswapd)
return 0;
pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
if (IS_ERR(pgdat->kswapd)) {
/* failure at boot is fatal */
BUG_ON(system_state == SYSTEM_BOOTING);
printk("Failed to start kswapd on node %d\n",nid);
ret = -1;
}
return ret;
}
/*
* Called by memory hotplug when all memory in a node is offlined. Caller must
* hold lock_memory_hotplug().
*/
void kswapd_stop(int nid)
{
struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
if (kswapd) {
kthread_stop(kswapd);
NODE_DATA(nid)->kswapd = NULL;
}
}
static int __init kswapd_init(void)
{
int nid;
swap_setup();
for_each_node_state(nid, N_HIGH_MEMORY)
kswapd_run(nid);
hotcpu_notifier(cpu_callback, 0);
return 0;
}
module_init(kswapd_init)
#ifdef CONFIG_NUMA
/*
* Zone reclaim mode
*
* If non-zero call zone_reclaim when the number of free pages falls below
* the watermarks.
*/
int zone_reclaim_mode __read_mostly;
#define RECLAIM_OFF 0
#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
/*
* Priority for ZONE_RECLAIM. This determines the fraction of pages
* of a node considered for each zone_reclaim. 4 scans 1/16th of
* a zone.
*/
#define ZONE_RECLAIM_PRIORITY 4
/*
* Percentage of pages in a zone that must be unmapped for zone_reclaim to
* occur.
*/
int sysctl_min_unmapped_ratio = 1;
/*
* If the number of slab pages in a zone grows beyond this percentage then
* slab reclaim needs to occur.
*/
int sysctl_min_slab_ratio = 5;
static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
{
unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
zone_page_state(zone, NR_ACTIVE_FILE);
/*
* It's possible for there to be more file mapped pages than
* accounted for by the pages on the file LRU lists because
* tmpfs pages accounted for as ANON can also be FILE_MAPPED
*/
return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
}
/* Work out how many page cache pages we can reclaim in this reclaim_mode */
static long zone_pagecache_reclaimable(struct zone *zone)
{
long nr_pagecache_reclaimable;
long delta = 0;
/*
* If RECLAIM_SWAP is set, then all file pages are considered
* potentially reclaimable. Otherwise, we have to worry about
* pages like swapcache and zone_unmapped_file_pages() provides
* a better estimate
*/
if (zone_reclaim_mode & RECLAIM_SWAP)
nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
else
nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
/* If we can't clean pages, remove dirty pages from consideration */
if (!(zone_reclaim_mode & RECLAIM_WRITE))
delta += zone_page_state(zone, NR_FILE_DIRTY);
/* Watch for any possible underflows due to delta */
if (unlikely(delta > nr_pagecache_reclaimable))
delta = nr_pagecache_reclaimable;
return nr_pagecache_reclaimable - delta;
}
/*
* Try to free up some pages from this zone through reclaim.
*/
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
/* Minimum pages needed in order to stay on node */
const unsigned long nr_pages = 1 << order;
struct task_struct *p = current;
struct reclaim_state reclaim_state;
int priority;
struct scan_control sc = {
.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
.may_swap = 1,
.nr_to_reclaim = max_t(unsigned long, nr_pages,
SWAP_CLUSTER_MAX),
.gfp_mask = gfp_mask,
.swappiness = vm_swappiness,
.order = order,
};
struct shrink_control shrink = {
.gfp_mask = sc.gfp_mask,
};
unsigned long nr_slab_pages0, nr_slab_pages1;
cond_resched();
/*
* We need to be able to allocate from the reserves for RECLAIM_SWAP
* and we also need to be able to write out pages for RECLAIM_WRITE
* and RECLAIM_SWAP.
*/
p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
lockdep_set_current_reclaim_state(gfp_mask);
reclaim_state.reclaimed_slab = 0;
p->reclaim_state = &reclaim_state;
if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
/*
* Free memory by calling shrink zone with increasing
* priorities until we have enough memory freed.
*/
priority = ZONE_RECLAIM_PRIORITY;
do {
shrink_zone(priority, zone, &sc);
priority--;
} while (priority >= 0 && sc.nr_reclaimed < nr_pages);
}
nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
if (nr_slab_pages0 > zone->min_slab_pages) {
/*
* shrink_slab() does not currently allow us to determine how
* many pages were freed in this zone. So we take the current
* number of slab pages and shake the slab until it is reduced
* by the same nr_pages that we used for reclaiming unmapped
* pages.
*
* Note that shrink_slab will free memory on all zones and may
* take a long time.
*/
for (;;) {
unsigned long lru_pages = zone_reclaimable_pages(zone);
/* No reclaimable slab or very low memory pressure */
if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
break;
/* Freed enough memory */
nr_slab_pages1 = zone_page_state(zone,
NR_SLAB_RECLAIMABLE);
if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
break;
}
/*
* Update nr_reclaimed by the number of slab pages we
* reclaimed from this zone.
*/
nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
if (nr_slab_pages1 < nr_slab_pages0)
sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
}
p->reclaim_state = NULL;
current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
lockdep_clear_current_reclaim_state();
return sc.nr_reclaimed >= nr_pages;
}
int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
int node_id;
int ret;
/*
* Zone reclaim reclaims unmapped file backed pages and
* slab pages if we are over the defined limits.
*
* A small portion of unmapped file backed pages is needed for
* file I/O otherwise pages read by file I/O will be immediately
* thrown out if the zone is overallocated. So we do not reclaim
* if less than a specified percentage of the zone is used by
* unmapped file backed pages.
*/
if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
return ZONE_RECLAIM_FULL;
if (zone->all_unreclaimable)
return ZONE_RECLAIM_FULL;
/*
* Do not scan if the allocation should not be delayed.
*/
if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
return ZONE_RECLAIM_NOSCAN;
/*
* Only run zone reclaim on the local zone or on zones that do not
* have associated processors. This will favor the local processor
* over remote processors and spread off node memory allocations
* as wide as possible.
*/
node_id = zone_to_nid(zone);
if (node_state(node_id, N_CPU) && node_id != numa_node_id())
return ZONE_RECLAIM_NOSCAN;
if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
return ZONE_RECLAIM_NOSCAN;
ret = __zone_reclaim(zone, gfp_mask, order);
zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
if (!ret)
count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
return ret;
}
#endif
/*
* page_evictable - test whether a page is evictable
* @page: the page to test
* @vma: the VMA in which the page is or will be mapped, may be NULL
*
* Test whether page is evictable--i.e., should be placed on active/inactive
* lists vs unevictable list. The vma argument is !NULL when called from the
* fault path to determine how to instantate a new page.
*
* Reasons page might not be evictable:
* (1) page's mapping marked unevictable
* (2) page is part of an mlocked VMA
*
*/
int page_evictable(struct page *page, struct vm_area_struct *vma)
{
if (mapping_unevictable(page_mapping(page)))
return 0;
if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
return 0;
return 1;
}
/**
* check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
* @page: page to check evictability and move to appropriate lru list
* @zone: zone page is in
*
* Checks a page for evictability and moves the page to the appropriate
* zone lru list.
*
* Restrictions: zone->lru_lock must be held, page must be on LRU and must
* have PageUnevictable set.
*/
static void check_move_unevictable_page(struct page *page, struct zone *zone)
{
VM_BUG_ON(PageActive(page));
retry:
ClearPageUnevictable(page);
if (page_evictable(page, NULL)) {
enum lru_list l = page_lru_base_type(page);
__dec_zone_state(zone, NR_UNEVICTABLE);
list_move(&page->lru, &zone->lru[l].list);
mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
__inc_zone_state(zone, NR_INACTIVE_ANON + l);
__count_vm_event(UNEVICTABLE_PGRESCUED);
} else {
/*
* rotate unevictable list
*/
SetPageUnevictable(page);
list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
if (page_evictable(page, NULL))
goto retry;
}
}
/**
* scan_mapping_unevictable_pages - scan an address space for evictable pages
* @mapping: struct address_space to scan for evictable pages
*
* Scan all pages in mapping. Check unevictable pages for
* evictability and move them to the appropriate zone lru list.
*/
void scan_mapping_unevictable_pages(struct address_space *mapping)
{
pgoff_t next = 0;
pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
PAGE_CACHE_SHIFT;
struct zone *zone;
struct pagevec pvec;
if (mapping->nrpages == 0)
return;
pagevec_init(&pvec, 0);
while (next < end &&
pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
int i;
int pg_scanned = 0;
zone = NULL;
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
pgoff_t page_index = page->index;
struct zone *pagezone = page_zone(page);
pg_scanned++;
if (page_index > next)
next = page_index;
next++;
if (pagezone != zone) {
if (zone)
spin_unlock_irq(&zone->lru_lock);
zone = pagezone;
spin_lock_irq(&zone->lru_lock);
}
if (PageLRU(page) && PageUnevictable(page))
check_move_unevictable_page(page, zone);
}
if (zone)
spin_unlock_irq(&zone->lru_lock);
pagevec_release(&pvec);
count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
}
}
/**
* scan_zone_unevictable_pages - check unevictable list for evictable pages
* @zone - zone of which to scan the unevictable list
*
* Scan @zone's unevictable LRU lists to check for pages that have become
* evictable. Move those that have to @zone's inactive list where they
* become candidates for reclaim, unless shrink_inactive_zone() decides
* to reactivate them. Pages that are still unevictable are rotated
* back onto @zone's unevictable list.
*/
#define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
static void scan_zone_unevictable_pages(struct zone *zone)
{
struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
unsigned long scan;
unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
while (nr_to_scan > 0) {
unsigned long batch_size = min(nr_to_scan,
SCAN_UNEVICTABLE_BATCH_SIZE);
spin_lock_irq(&zone->lru_lock);
for (scan = 0; scan < batch_size; scan++) {
struct page *page = lru_to_page(l_unevictable);
if (!trylock_page(page))
continue;
prefetchw_prev_lru_page(page, l_unevictable, flags);
if (likely(PageLRU(page) && PageUnevictable(page)))
check_move_unevictable_page(page, zone);
unlock_page(page);
}
spin_unlock_irq(&zone->lru_lock);
nr_to_scan -= batch_size;
}
}
/**
* scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
*
* A really big hammer: scan all zones' unevictable LRU lists to check for
* pages that have become evictable. Move those back to the zones'
* inactive list where they become candidates for reclaim.
* This occurs when, e.g., we have unswappable pages on the unevictable lists,
* and we add swap to the system. As such, it runs in the context of a task
* that has possibly/probably made some previously unevictable pages
* evictable.
*/
static void scan_all_zones_unevictable_pages(void)
{
struct zone *zone;
for_each_zone(zone) {
scan_zone_unevictable_pages(zone);
}
}
/*
* scan_unevictable_pages [vm] sysctl handler. On demand re-scan of
* all nodes' unevictable lists for evictable pages
*/
unsigned long scan_unevictable_pages;
int scan_unevictable_handler(struct ctl_table *table, int write,
void __user *buffer,
size_t *length, loff_t *ppos)
{
proc_doulongvec_minmax(table, write, buffer, length, ppos);
if (write && *(unsigned long *)table->data)
scan_all_zones_unevictable_pages();
scan_unevictable_pages = 0;
return 0;
}
#ifdef CONFIG_NUMA
/*
* per node 'scan_unevictable_pages' attribute. On demand re-scan of
* a specified node's per zone unevictable lists for evictable pages.
*/
static ssize_t read_scan_unevictable_node(struct sys_device *dev,
struct sysdev_attribute *attr,
char *buf)
{
return sprintf(buf, "0\n"); /* always zero; should fit... */
}
static ssize_t write_scan_unevictable_node(struct sys_device *dev,
struct sysdev_attribute *attr,
const char *buf, size_t count)
{
struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
struct zone *zone;
unsigned long res;
unsigned long req = strict_strtoul(buf, 10, &res);
if (!req)
return 1; /* zero is no-op */
for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
if (!populated_zone(zone))
continue;
scan_zone_unevictable_pages(zone);
}
return 1;
}
static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
read_scan_unevictable_node,
write_scan_unevictable_node);
int scan_unevictable_register_node(struct node *node)
{
return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
}
void scan_unevictable_unregister_node(struct node *node)
{
sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
}
#endif