Commit 41508bb7 authored by Coly Li's avatar Coly Li Committed by Jens Axboe

bcache: add comments for mutex_lock(&b->write_lock)

When accessing or modifying BTREE_NODE_dirty bit, it is not always
necessary to acquire b->write_lock. In bch_btree_cache_free() and
mca_reap() acquiring b->write_lock is necessary, and this patch adds
comments to explain why mutex_lock(&b->write_lock) is necessary for
checking or clearing BTREE_NODE_dirty bit there.
Signed-off-by: default avatarColy Li <colyli@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent e5ec5f47
...@@ -659,6 +659,11 @@ static int mca_reap(struct btree *b, unsigned int min_order, bool flush) ...@@ -659,6 +659,11 @@ static int mca_reap(struct btree *b, unsigned int min_order, bool flush)
up(&b->io_mutex); up(&b->io_mutex);
} }
/*
* BTREE_NODE_dirty might be cleared in btree_flush_btree() by
* __bch_btree_node_write(). To avoid an extra flush, acquire
* b->write_lock before checking BTREE_NODE_dirty bit.
*/
mutex_lock(&b->write_lock); mutex_lock(&b->write_lock);
if (btree_node_dirty(b)) if (btree_node_dirty(b))
__bch_btree_node_write(b, &cl); __bch_btree_node_write(b, &cl);
...@@ -782,6 +787,11 @@ void bch_btree_cache_free(struct cache_set *c) ...@@ -782,6 +787,11 @@ void bch_btree_cache_free(struct cache_set *c)
while (!list_empty(&c->btree_cache)) { while (!list_empty(&c->btree_cache)) {
b = list_first_entry(&c->btree_cache, struct btree, list); b = list_first_entry(&c->btree_cache, struct btree, list);
/*
* This function is called by cache_set_free(), no I/O
* request on cache now, it is unnecessary to acquire
* b->write_lock before clearing BTREE_NODE_dirty anymore.
*/
if (btree_node_dirty(b)) { if (btree_node_dirty(b)) {
btree_complete_write(b, btree_current_write(b)); btree_complete_write(b, btree_current_write(b));
clear_bit(BTREE_NODE_dirty, &b->flags); clear_bit(BTREE_NODE_dirty, &b->flags);
......
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