310 lines
10 KiB
C
310 lines
10 KiB
C
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#ifndef _BCACHE_BTREE_H
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#define _BCACHE_BTREE_H
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/*
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* THE BTREE:
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*
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* At a high level, bcache's btree is relatively standard b+ tree. All keys and
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* pointers are in the leaves; interior nodes only have pointers to the child
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* nodes.
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*
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* In the interior nodes, a struct bkey always points to a child btree node, and
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* the key is the highest key in the child node - except that the highest key in
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* an interior node is always MAX_KEY. The size field refers to the size on disk
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* of the child node - this would allow us to have variable sized btree nodes
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* (handy for keeping the depth of the btree 1 by expanding just the root).
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*
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* Btree nodes are themselves log structured, but this is hidden fairly
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* thoroughly. Btree nodes on disk will in practice have extents that overlap
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* (because they were written at different times), but in memory we never have
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* overlapping extents - when we read in a btree node from disk, the first thing
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* we do is resort all the sets of keys with a mergesort, and in the same pass
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* we check for overlapping extents and adjust them appropriately.
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*
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* struct btree_op is a central interface to the btree code. It's used for
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* specifying read vs. write locking, and the embedded closure is used for
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* waiting on IO or reserve memory.
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*
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* BTREE CACHE:
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*
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* Btree nodes are cached in memory; traversing the btree might require reading
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* in btree nodes which is handled mostly transparently.
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*
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* bch_btree_node_get() looks up a btree node in the cache and reads it in from
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* disk if necessary. This function is almost never called directly though - the
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* btree() macro is used to get a btree node, call some function on it, and
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* unlock the node after the function returns.
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*
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* The root is special cased - it's taken out of the cache's lru (thus pinning
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* it in memory), so we can find the root of the btree by just dereferencing a
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* pointer instead of looking it up in the cache. This makes locking a bit
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* tricky, since the root pointer is protected by the lock in the btree node it
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* points to - the btree_root() macro handles this.
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*
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* In various places we must be able to allocate memory for multiple btree nodes
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* in order to make forward progress. To do this we use the btree cache itself
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* as a reserve; if __get_free_pages() fails, we'll find a node in the btree
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* cache we can reuse. We can't allow more than one thread to be doing this at a
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* time, so there's a lock, implemented by a pointer to the btree_op closure -
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* this allows the btree_root() macro to implicitly release this lock.
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*
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* BTREE IO:
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*
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* Btree nodes never have to be explicitly read in; bch_btree_node_get() handles
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* this.
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*
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* For writing, we have two btree_write structs embeddded in struct btree - one
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* write in flight, and one being set up, and we toggle between them.
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*
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* Writing is done with a single function - bch_btree_write() really serves two
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* different purposes and should be broken up into two different functions. When
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* passing now = false, it merely indicates that the node is now dirty - calling
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* it ensures that the dirty keys will be written at some point in the future.
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*
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* When passing now = true, bch_btree_write() causes a write to happen
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* "immediately" (if there was already a write in flight, it'll cause the write
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* to happen as soon as the previous write completes). It returns immediately
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* though - but it takes a refcount on the closure in struct btree_op you passed
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* to it, so a closure_sync() later can be used to wait for the write to
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* complete.
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*
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* This is handy because btree_split() and garbage collection can issue writes
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* in parallel, reducing the amount of time they have to hold write locks.
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*
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* LOCKING:
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*
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* When traversing the btree, we may need write locks starting at some level -
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* inserting a key into the btree will typically only require a write lock on
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* the leaf node.
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*
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* This is specified with the lock field in struct btree_op; lock = 0 means we
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* take write locks at level <= 0, i.e. only leaf nodes. bch_btree_node_get()
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* checks this field and returns the node with the appropriate lock held.
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*
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* If, after traversing the btree, the insertion code discovers it has to split
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* then it must restart from the root and take new locks - to do this it changes
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* the lock field and returns -EINTR, which causes the btree_root() macro to
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* loop.
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*
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* Handling cache misses require a different mechanism for upgrading to a write
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* lock. We do cache lookups with only a read lock held, but if we get a cache
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* miss and we wish to insert this data into the cache, we have to insert a
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* placeholder key to detect races - otherwise, we could race with a write and
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* overwrite the data that was just written to the cache with stale data from
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* the backing device.
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*
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* For this we use a sequence number that write locks and unlocks increment - to
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* insert the check key it unlocks the btree node and then takes a write lock,
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* and fails if the sequence number doesn't match.
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*/
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#include "bset.h"
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#include "debug.h"
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struct btree_write {
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atomic_t *journal;
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/* If btree_split() frees a btree node, it writes a new pointer to that
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* btree node indicating it was freed; it takes a refcount on
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* c->prio_blocked because we can't write the gens until the new
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* pointer is on disk. This allows btree_write_endio() to release the
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* refcount that btree_split() took.
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*/
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int prio_blocked;
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};
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struct btree {
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/* Hottest entries first */
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struct hlist_node hash;
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/* Key/pointer for this btree node */
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BKEY_PADDED(key);
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/* Single bit - set when accessed, cleared by shrinker */
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unsigned long accessed;
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unsigned long seq;
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struct rw_semaphore lock;
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struct cache_set *c;
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struct btree *parent;
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struct mutex write_lock;
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unsigned long flags;
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uint16_t written; /* would be nice to kill */
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uint8_t level;
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struct btree_keys keys;
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/* For outstanding btree writes, used as a lock - protects write_idx */
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struct closure io;
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struct semaphore io_mutex;
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struct list_head list;
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struct delayed_work work;
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struct btree_write writes[2];
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struct bio *bio;
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};
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#define BTREE_FLAG(flag) \
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static inline bool btree_node_ ## flag(struct btree *b) \
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{ return test_bit(BTREE_NODE_ ## flag, &b->flags); } \
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\
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static inline void set_btree_node_ ## flag(struct btree *b) \
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{ set_bit(BTREE_NODE_ ## flag, &b->flags); } \
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enum btree_flags {
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BTREE_NODE_io_error,
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BTREE_NODE_dirty,
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BTREE_NODE_write_idx,
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};
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BTREE_FLAG(io_error);
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BTREE_FLAG(dirty);
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BTREE_FLAG(write_idx);
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static inline struct btree_write *btree_current_write(struct btree *b)
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{
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return b->writes + btree_node_write_idx(b);
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}
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static inline struct btree_write *btree_prev_write(struct btree *b)
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{
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return b->writes + (btree_node_write_idx(b) ^ 1);
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}
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static inline struct bset *btree_bset_first(struct btree *b)
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{
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return b->keys.set->data;
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}
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static inline struct bset *btree_bset_last(struct btree *b)
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{
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return bset_tree_last(&b->keys)->data;
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}
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static inline unsigned bset_block_offset(struct btree *b, struct bset *i)
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{
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return bset_sector_offset(&b->keys, i) >> b->c->block_bits;
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}
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static inline void set_gc_sectors(struct cache_set *c)
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{
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atomic_set(&c->sectors_to_gc, c->sb.bucket_size * c->nbuckets / 16);
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}
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void bkey_put(struct cache_set *c, struct bkey *k);
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/* Looping macros */
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#define for_each_cached_btree(b, c, iter) \
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for (iter = 0; \
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iter < ARRAY_SIZE((c)->bucket_hash); \
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iter++) \
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hlist_for_each_entry_rcu((b), (c)->bucket_hash + iter, hash)
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/* Recursing down the btree */
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struct btree_op {
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/* for waiting on btree reserve in btree_split() */
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wait_queue_t wait;
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/* Btree level at which we start taking write locks */
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short lock;
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unsigned insert_collision:1;
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};
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static inline void bch_btree_op_init(struct btree_op *op, int write_lock_level)
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{
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memset(op, 0, sizeof(struct btree_op));
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init_wait(&op->wait);
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op->lock = write_lock_level;
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}
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static inline void rw_lock(bool w, struct btree *b, int level)
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{
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w ? down_write_nested(&b->lock, level + 1)
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: down_read_nested(&b->lock, level + 1);
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if (w)
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b->seq++;
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}
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static inline void rw_unlock(bool w, struct btree *b)
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{
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if (w)
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b->seq++;
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(w ? up_write : up_read)(&b->lock);
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}
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void bch_btree_node_read_done(struct btree *);
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void __bch_btree_node_write(struct btree *, struct closure *);
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void bch_btree_node_write(struct btree *, struct closure *);
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void bch_btree_set_root(struct btree *);
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struct btree *__bch_btree_node_alloc(struct cache_set *, struct btree_op *,
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int, bool, struct btree *);
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struct btree *bch_btree_node_get(struct cache_set *, struct btree_op *,
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struct bkey *, int, bool, struct btree *);
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int bch_btree_insert_check_key(struct btree *, struct btree_op *,
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struct bkey *);
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int bch_btree_insert(struct cache_set *, struct keylist *,
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atomic_t *, struct bkey *);
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int bch_gc_thread_start(struct cache_set *);
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void bch_initial_gc_finish(struct cache_set *);
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void bch_moving_gc(struct cache_set *);
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int bch_btree_check(struct cache_set *);
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void bch_initial_mark_key(struct cache_set *, int, struct bkey *);
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static inline void wake_up_gc(struct cache_set *c)
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{
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wake_up(&c->gc_wait);
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}
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#define MAP_DONE 0
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#define MAP_CONTINUE 1
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#define MAP_ALL_NODES 0
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#define MAP_LEAF_NODES 1
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#define MAP_END_KEY 1
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typedef int (btree_map_nodes_fn)(struct btree_op *, struct btree *);
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int __bch_btree_map_nodes(struct btree_op *, struct cache_set *,
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struct bkey *, btree_map_nodes_fn *, int);
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static inline int bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
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struct bkey *from, btree_map_nodes_fn *fn)
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{
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return __bch_btree_map_nodes(op, c, from, fn, MAP_ALL_NODES);
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}
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static inline int bch_btree_map_leaf_nodes(struct btree_op *op,
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struct cache_set *c,
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struct bkey *from,
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btree_map_nodes_fn *fn)
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{
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return __bch_btree_map_nodes(op, c, from, fn, MAP_LEAF_NODES);
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}
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typedef int (btree_map_keys_fn)(struct btree_op *, struct btree *,
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struct bkey *);
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int bch_btree_map_keys(struct btree_op *, struct cache_set *,
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struct bkey *, btree_map_keys_fn *, int);
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typedef bool (keybuf_pred_fn)(struct keybuf *, struct bkey *);
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void bch_keybuf_init(struct keybuf *);
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void bch_refill_keybuf(struct cache_set *, struct keybuf *,
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struct bkey *, keybuf_pred_fn *);
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bool bch_keybuf_check_overlapping(struct keybuf *, struct bkey *,
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struct bkey *);
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void bch_keybuf_del(struct keybuf *, struct keybuf_key *);
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struct keybuf_key *bch_keybuf_next(struct keybuf *);
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struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *, struct keybuf *,
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struct bkey *, keybuf_pred_fn *);
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#endif
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