- 根目录:
- drivers
- md
- bcache
- btree.h
#ifndef _BCACHE_BTREE_H
#define _BCACHE_BTREE_H
/*
* THE BTREE:
*
* At a high level, bcache's btree is relatively standard b+ tree. All keys and
* pointers are in the leaves; interior nodes only have pointers to the child
* nodes.
*
* In the interior nodes, a struct bkey always points to a child btree node, and
* the key is the highest key in the child node - except that the highest key in
* an interior node is always MAX_KEY. The size field refers to the size on disk
* of the child node - this would allow us to have variable sized btree nodes
* (handy for keeping the depth of the btree 1 by expanding just the root).
*
* Btree nodes are themselves log structured, but this is hidden fairly
* thoroughly. Btree nodes on disk will in practice have extents that overlap
* (because they were written at different times), but in memory we never have
* overlapping extents - when we read in a btree node from disk, the first thing
* we do is resort all the sets of keys with a mergesort, and in the same pass
* we check for overlapping extents and adjust them appropriately.
*
* struct btree_op is a central interface to the btree code. It's used for
* specifying read vs. write locking, and the embedded closure is used for
* waiting on IO or reserve memory.
*
* BTREE CACHE:
*
* Btree nodes are cached in memory; traversing the btree might require reading
* in btree nodes which is handled mostly transparently.
*
* bch_btree_node_get() looks up a btree node in the cache and reads it in from
* disk if necessary. This function is almost never called directly though - the
* btree() macro is used to get a btree node, call some function on it, and
* unlock the node after the function returns.
*
* The root is special cased - it's taken out of the cache's lru (thus pinning
* it in memory), so we can find the root of the btree by just dereferencing a
* pointer instead of looking it up in the cache. This makes locking a bit
* tricky, since the root pointer is protected by the lock in the btree node it
* points to - the btree_root() macro handles this.
*
* In various places we must be able to allocate memory for multiple btree nodes
* in order to make forward progress. To do this we use the btree cache itself
* as a reserve; if __get_free_pages() fails, we'll find a node in the btree
* cache we can reuse. We can't allow more than one thread to be doing this at a
* time, so there's a lock, implemented by a pointer to the btree_op closure -
* this allows the btree_root() macro to implicitly release this lock.
*
* BTREE IO:
*
* Btree nodes never have to be explicitly read in; bch_btree_node_get() handles
* this.
*
* For writing, we have two btree_write structs embeddded in struct btree - one
* write in flight, and one being set up, and we toggle between them.
*
* Writing is done with a single function - bch_btree_write() really serves two
* different purposes and should be broken up into two different functions. When
* passing now = false, it merely indicates that the node is now dirty - calling
* it ensures that the dirty keys will be written at some point in the future.
*
* When passing now = true, bch_btree_write() causes a write to happen
* "immediately" (if there was already a write in flight, it'll cause the write
* to happen as soon as the previous write completes). It returns immediately
* though - but it takes a refcount on the closure in struct btree_op you passed
* to it, so a closure_sync() later can be used to wait for the write to
* complete.
*
* This is handy because btree_split() and garbage collection can issue writes
* in parallel, reducing the amount of time they have to hold write locks.
*
* LOCKING:
*
* When traversing the btree, we may need write locks starting at some level -
* inserting a key into the btree will typically only require a write lock on
* the leaf node.
*
* This is specified with the lock field in struct btree_op; lock = 0 means we
* take write locks at level <= 0, i.e. only leaf nodes. bch_btree_node_get()
* checks this field and returns the node with the appropriate lock held.
*
* If, after traversing the btree, the insertion code discovers it has to split
* then it must restart from the root and take new locks - to do this it changes
* the lock field and returns -EINTR, which causes the btree_root() macro to
* loop.
*
* Handling cache misses require a different mechanism for upgrading to a write
* lock. We do cache lookups with only a read lock held, but if we get a cache
* miss and we wish to insert this data into the cache, we have to insert a
* placeholder key to detect races - otherwise, we could race with a write and
* overwrite the data that was just written to the cache with stale data from
* the backing device.
*
* For this we use a sequence number that write locks and unlocks increment - to
* insert the check key it unlocks the btree node and then takes a write lock,
* and fails if the sequence number doesn't match.
*/
#include "bset.h"
#include "debug.h"
struct btree_write {
struct closure *owner;
atomic_t *journal;
/* If btree_split() frees a btree node, it writes a new pointer to that
* btree node indicating it was freed; it takes a refcount on
* c->prio_blocked because we can't write the gens until the new
* pointer is on disk. This allows btree_write_endio() to release the
* refcount that btree_split() took.
*/
int prio_blocked;
};
struct btree {
/* Hottest entries first */
struct hlist_node hash;
/* Key/pointer for this btree node */
BKEY_PADDED(key);
/* Single bit - set when accessed, cleared by shrinker */
unsigned long accessed;
unsigned long seq;
struct rw_semaphore lock;
struct cache_set *c;
unsigned long flags;
uint16_t written; /* would be nice to kill */
uint8_t level;
uint8_t nsets;
uint8_t page_order;
/*
* Set of sorted keys - the real btree node - plus a binary search tree
*
* sets[0] is special; set[0]->tree, set[0]->prev and set[0]->data point
* to the memory we have allocated for this btree node. Additionally,
* set[0]->data points to the entire btree node as it exists on disk.
*/
struct bset_tree sets[MAX_BSETS];
/* Used to refcount bio splits, also protects b->bio */
struct closure_with_waitlist io;
/* Gets transferred to w->prio_blocked - see the comment there */
int prio_blocked;
struct list_head list;
struct delayed_work work;
uint64_t io_start_time;
struct btree_write writes[2];
struct bio *bio;
};
#define BTREE_FLAG(flag) \
static inline bool btree_node_ ## flag(struct btree *b) \
{ return test_bit(BTREE_NODE_ ## flag, &b->flags); } \
\
static inline void set_btree_node_ ## flag(struct btree *b) \
{ set_bit(BTREE_NODE_ ## flag, &b->flags); } \
enum btree_flags {
BTREE_NODE_read_done,
BTREE_NODE_io_error,
BTREE_NODE_dirty,
BTREE_NODE_write_idx,
};
BTREE_FLAG(read_done);
BTREE_FLAG(io_error);
BTREE_FLAG(dirty);
BTREE_FLAG(write_idx);
static inline struct btree_write *btree_current_write(struct btree *b)
{
return b->writes + btree_node_write_idx(b);
}
static inline struct btree_write *btree_prev_write(struct btree *b)
{
return b->writes + (btree_node_write_idx(b) ^ 1);
}
static inline unsigned bset_offset(struct btree *b, struct bset *i)
{
return (((size_t) i) - ((size_t) b->sets->data)) >> 9;
}
static inline struct bset *write_block(struct btree *b)
{
return ((void *) b->sets[0].data) + b->written * block_bytes(b->c);
}
static inline bool bset_written(struct btree *b, struct bset_tree *t)
{
return t->data < write_block(b);
}
static inline bool bkey_written(struct btree *b, struct bkey *k)
{
return k < write_block(b)->start;
}
static inline void set_gc_sectors(struct cache_set *c)
{
atomic_set(&c->sectors_to_gc, c->sb.bucket_size * c->nbuckets / 8);
}
static inline bool bch_ptr_invalid(struct btree *b, const struct bkey *k)
{
return __bch_ptr_invalid(b->c, b->level, k);
}
static inline struct bkey *bch_btree_iter_init(struct btree *b,
struct btree_iter *iter,
struct bkey *search)
{
return __bch_btree_iter_init(b, iter, search, b->sets);
}
/* Looping macros */
#define for_each_cached_btree(b, c, iter) \
for (iter = 0; \
iter < ARRAY_SIZE((c)->bucket_hash); \
iter++) \
hlist_for_each_entry_rcu((b), (c)->bucket_hash + iter, hash)
#define for_each_key_filter(b, k, iter, filter) \
for (bch_btree_iter_init((b), (iter), NULL); \
((k) = bch_btree_iter_next_filter((iter), b, filter));)
#define for_each_key(b, k, iter) \
for (bch_btree_iter_init((b), (iter), NULL); \
((k) = bch_btree_iter_next(iter));)
/* Recursing down the btree */
struct btree_op {
struct closure cl;
struct cache_set *c;
/* Journal entry we have a refcount on */
atomic_t *journal;
/* Bio to be inserted into the cache */
struct bio *cache_bio;
unsigned inode;
uint16_t write_prio;
/* Btree level at which we start taking write locks */
short lock;
/* Btree insertion type */
enum {
BTREE_INSERT,
BTREE_REPLACE
} type:8;
unsigned csum:1;
unsigned skip:1;
unsigned flush_journal:1;
unsigned insert_data_done:1;
unsigned lookup_done:1;
unsigned insert_collision:1;
/* Anything after this point won't get zeroed in do_bio_hook() */
/* Keys to be inserted */
struct keylist keys;
BKEY_PADDED(replace);
};
void bch_btree_op_init_stack(struct btree_op *);
static inline void rw_lock(bool w, struct btree *b, int level)
{
w ? down_write_nested(&b->lock, level + 1)
: down_read_nested(&b->lock, level + 1);
if (w)
b->seq++;
}
static inline void rw_unlock(bool w, struct btree *b)
{
#ifdef CONFIG_BCACHE_EDEBUG
unsigned i;
if (w &&
b->key.ptr[0] &&
btree_node_read_done(b))
for (i = 0; i <= b->nsets; i++)
bch_check_key_order(b, b->sets[i].data);
#endif
if (w)
b->seq++;
(w ? up_write : up_read)(&b->lock);
}
#define insert_lock(s, b) ((b)->level <= (s)->lock)
/*
* These macros are for recursing down the btree - they handle the details of
* locking and looking up nodes in the cache for you. They're best treated as
* mere syntax when reading code that uses them.
*
* op->lock determines whether we take a read or a write lock at a given depth.
* If you've got a read lock and find that you need a write lock (i.e. you're
* going to have to split), set op->lock and return -EINTR; btree_root() will
* call you again and you'll have the correct lock.
*/
/**
* btree - recurse down the btree on a specified key
* @fn: function to call, which will be passed the child node
* @key: key to recurse on
* @b: parent btree node
* @op: pointer to struct btree_op
*/
#define btree(fn, key, b, op, ...) \
({ \
int _r, l = (b)->level - 1; \
bool _w = l <= (op)->lock; \
struct btree *_b = bch_btree_node_get((b)->c, key, l, op); \
if (!IS_ERR(_b)) { \
_r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__); \
rw_unlock(_w, _b); \
} else \
_r = PTR_ERR(_b); \
_r; \
})
/**
* btree_root - call a function on the root of the btree
* @fn: function to call, which will be passed the child node
* @c: cache set
* @op: pointer to struct btree_op
*/
#define btree_root(fn, c, op, ...) \
({ \
int _r = -EINTR; \
do { \
struct btree *_b = (c)->root; \
bool _w = insert_lock(op, _b); \
rw_lock(_w, _b, _b->level); \
if (_b == (c)->root && \
_w == insert_lock(op, _b)) \
_r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__); \
rw_unlock(_w, _b); \
bch_cannibalize_unlock(c, &(op)->cl); \
} while (_r == -EINTR); \
\
_r; \
})
static inline bool should_split(struct btree *b)
{
struct bset *i = write_block(b);
return b->written >= btree_blocks(b) ||
(i->seq == b->sets[0].data->seq &&
b->written + __set_blocks(i, i->keys + 15, b->c)
> btree_blocks(b));
}
void bch_btree_read_done(struct closure *);
void bch_btree_read(struct btree *);
void bch_btree_write(struct btree *b, bool now, struct btree_op *op);
void bch_cannibalize_unlock(struct cache_set *, struct closure *);
void bch_btree_set_root(struct btree *);
struct btree *bch_btree_node_alloc(struct cache_set *, int, struct closure *);
struct btree *bch_btree_node_get(struct cache_set *, struct bkey *,
int, struct btree_op *);
bool bch_btree_insert_keys(struct btree *, struct btree_op *);
bool bch_btree_insert_check_key(struct btree *, struct btree_op *,
struct bio *);
int bch_btree_insert(struct btree_op *, struct cache_set *);
int bch_btree_search_recurse(struct btree *, struct btree_op *);
void bch_queue_gc(struct cache_set *);
size_t bch_btree_gc_finish(struct cache_set *);
void bch_moving_gc(struct closure *);
int bch_btree_check(struct cache_set *, struct btree_op *);
uint8_t __bch_btree_mark_key(struct cache_set *, int, struct bkey *);
void bch_keybuf_init(struct keybuf *, keybuf_pred_fn *);
void bch_refill_keybuf(struct cache_set *, struct keybuf *, struct bkey *);
bool bch_keybuf_check_overlapping(struct keybuf *, struct bkey *,
struct bkey *);
void bch_keybuf_del(struct keybuf *, struct keybuf_key *);
struct keybuf_key *bch_keybuf_next(struct keybuf *);
struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *,
struct keybuf *, struct bkey *);
#endif