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![Coly Li](/assets/img/avatar_default.png)
Commit8e7102273f
("bcache: make bch_btree_check() to be multithreaded") makes bch_btree_check() to be much faster when checking all btree nodes during cache device registration. But it isn't in ideal shap yet, still can be improved. This patch does the following thing to improve current parallel btree nodes check by multiple threads in bch_btree_check(), - Add read lock to root node while checking all the btree nodes with multiple threads. Although currently it is not mandatory but it is good to have a read lock in code logic. - Remove local variable 'char name[32]', and generate kernel thread name string directly when calling kthread_run(). - Allocate local variable "struct btree_check_state check_state" on the stack and avoid unnecessary dynamic memory allocation for it. - Reduce BCH_BTR_CHKTHREAD_MAX from 64 to 12 which is enough indeed. - Increase check_state->started to count created kernel thread after it succeeds to create. - When wait for all checking kernel threads to finish, use wait_event() to replace wait_event_interruptible(). With this change, the code is more clear, and some potential error conditions are avoided. Fixes:8e7102273f
("bcache: make bch_btree_check() to be multithreaded") Signed-off-by: Coly Li <colyli@suse.de> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20220524102336.10684-2-colyli@suse.de Signed-off-by: Jens Axboe <axboe@kernel.dk>
416 lines
14 KiB
C
416 lines
14 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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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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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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BTREE_NODE_journal_flush,
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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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BTREE_FLAG(journal_flush);
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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 int 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->cache->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_entry_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 int insert_collision:1;
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};
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struct btree_check_state;
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struct btree_check_info {
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struct btree_check_state *state;
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struct task_struct *thread;
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int result;
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};
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#define BCH_BTR_CHKTHREAD_MAX 12
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struct btree_check_state {
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struct cache_set *c;
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int total_threads;
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int key_idx;
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spinlock_t idx_lock;
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atomic_t started;
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atomic_t enough;
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wait_queue_head_t wait;
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struct btree_check_info infos[BCH_BTR_CHKTHREAD_MAX];
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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 *b);
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void __bch_btree_node_write(struct btree *b, struct closure *parent);
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void bch_btree_node_write(struct btree *b, struct closure *parent);
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void bch_btree_set_root(struct btree *b);
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struct btree *__bch_btree_node_alloc(struct cache_set *c, struct btree_op *op,
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int level, bool wait,
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struct btree *parent);
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struct btree *bch_btree_node_get(struct cache_set *c, struct btree_op *op,
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struct bkey *k, int level, bool write,
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struct btree *parent);
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int bch_btree_insert_check_key(struct btree *b, struct btree_op *op,
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struct bkey *check_key);
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int bch_btree_insert(struct cache_set *c, struct keylist *keys,
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atomic_t *journal_ref, struct bkey *replace_key);
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int bch_gc_thread_start(struct cache_set *c);
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void bch_initial_gc_finish(struct cache_set *c);
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void bch_moving_gc(struct cache_set *c);
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int bch_btree_check(struct cache_set *c);
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void bch_initial_mark_key(struct cache_set *c, int level, struct bkey *k);
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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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static inline void force_wake_up_gc(struct cache_set *c)
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{
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/*
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* Garbage collection thread only works when sectors_to_gc < 0,
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* calling wake_up_gc() won't start gc thread if sectors_to_gc is
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* not a nagetive value.
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* Therefore sectors_to_gc is set to -1 here, before waking up
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* gc thread by calling wake_up_gc(). Then gc_should_run() will
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* give a chance to permit gc thread to run. "Give a chance" means
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* before going into gc_should_run(), there is still possibility
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* that c->sectors_to_gc being set to other positive value. So
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* this routine won't 100% make sure gc thread will be woken up
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* to run.
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*/
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atomic_set(&c->sectors_to_gc, -1);
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wake_up_gc(c);
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}
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/*
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* These macros are for recursing down the btree - they handle the details of
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* locking and looking up nodes in the cache for you. They're best treated as
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* mere syntax when reading code that uses them.
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*
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* op->lock determines whether we take a read or a write lock at a given depth.
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* If you've got a read lock and find that you need a write lock (i.e. you're
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* going to have to split), set op->lock and return -EINTR; btree_root() will
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* call you again and you'll have the correct lock.
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*/
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/**
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* btree - recurse down the btree on a specified key
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* @fn: function to call, which will be passed the child node
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* @key: key to recurse on
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* @b: parent btree node
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* @op: pointer to struct btree_op
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*/
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#define bcache_btree(fn, key, b, op, ...) \
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({ \
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int _r, l = (b)->level - 1; \
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bool _w = l <= (op)->lock; \
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struct btree *_child = bch_btree_node_get((b)->c, op, key, l, \
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_w, b); \
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if (!IS_ERR(_child)) { \
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_r = bch_btree_ ## fn(_child, op, ##__VA_ARGS__); \
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rw_unlock(_w, _child); \
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} else \
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_r = PTR_ERR(_child); \
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_r; \
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})
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/**
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* btree_root - call a function on the root of the btree
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* @fn: function to call, which will be passed the child node
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* @c: cache set
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* @op: pointer to struct btree_op
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*/
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#define bcache_btree_root(fn, c, op, ...) \
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({ \
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int _r = -EINTR; \
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do { \
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struct btree *_b = (c)->root; \
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bool _w = insert_lock(op, _b); \
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rw_lock(_w, _b, _b->level); \
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if (_b == (c)->root && \
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_w == insert_lock(op, _b)) { \
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_r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__); \
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} \
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rw_unlock(_w, _b); \
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bch_cannibalize_unlock(c); \
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if (_r == -EINTR) \
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schedule(); \
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} while (_r == -EINTR); \
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\
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finish_wait(&(c)->btree_cache_wait, &(op)->wait); \
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_r; \
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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 *b_op, struct btree *b);
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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, int flags);
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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 *op, struct btree *b,
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struct bkey *k);
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int bch_btree_map_keys(struct btree_op *op, struct cache_set *c,
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struct bkey *from, btree_map_keys_fn *fn, int flags);
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int bch_btree_map_keys_recurse(struct btree *b, struct btree_op *op,
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struct bkey *from, btree_map_keys_fn *fn,
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int flags);
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typedef bool (keybuf_pred_fn)(struct keybuf *buf, struct bkey *k);
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void bch_keybuf_init(struct keybuf *buf);
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void bch_refill_keybuf(struct cache_set *c, struct keybuf *buf,
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struct bkey *end, keybuf_pred_fn *pred);
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bool bch_keybuf_check_overlapping(struct keybuf *buf, struct bkey *start,
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struct bkey *end);
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void bch_keybuf_del(struct keybuf *buf, struct keybuf_key *w);
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struct keybuf_key *bch_keybuf_next(struct keybuf *buf);
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struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c,
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struct keybuf *buf,
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struct bkey *end,
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keybuf_pred_fn *pred);
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void bch_update_bucket_in_use(struct cache_set *c, struct gc_stat *stats);
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#endif
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