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: Coly Li colyli@suse.de Signed-off-by: Jens Axboe axboe@kernel.dk --- drivers/md/bcache/btree.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 3fbadf2058a65..9788b2ee6638f 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -655,6 +655,11 @@ static int mca_reap(struct btree *b, unsigned int min_order, bool flush) 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); if (btree_node_dirty(b)) __bch_btree_node_write(b, &cl); @@ -778,6 +783,11 @@ void bch_btree_cache_free(struct cache_set *c) while (!list_empty(&c->btree_cache)) { 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)) { btree_complete_write(b, btree_current_write(b)); clear_bit(BTREE_NODE_dirty, &b->flags);