[PATCH 5.2 18/37] bcache: only clear BTREE_NODE_dirty bit when it is set

Greg Kroah-Hartman
2019-09-13T13:21:15Z

In bch_btree_cache_free() and btree_node_free(), BTREE_NODE_dirty is
always set no matter btree node is dirty or not. The code looks like
this,
if (btree_node_dirty(b))
btree_complete_write(b, btree_current_write(b));
clear_bit(BTREE_NODE_dirty, &b->flags);

Indeed if btree_node_dirty(b) returns false, it means BTREE_NODE_dirty
bit is cleared, then it is unnecessary to clear the bit again.

This patch only clears BTREE_NODE_dirty when btree_node_dirty(b) is
true (the bit is set), to save a few CPU cycles.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
drivers/md/bcache/btree.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 773f5fdad25fb..3fbadf2058a65 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -778,10 +778,10 @@ 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);

- if (btree_node_dirty(b))
+ if (btree_node_dirty(b)) {
btree_complete_write(b, btree_current_write(b));
- clear_bit(BTREE_NODE_dirty, &b->flags);
-
+ clear_bit(BTREE_NODE_dirty, &b->flags);
+ }
mca_data_free(b);
}

@@ -1069,9 +1069,10 @@ static void btree_node_free(struct btree *b)

mutex_lock(&b->write_lock);

- if (btree_node_dirty(b))
+ if (btree_node_dirty(b)) {
btree_complete_write(b, btree_current_write(b));
- clear_bit(BTREE_NODE_dirty, &b->flags);
+ clear_bit(BTREE_NODE_dirty, &b->flags);
+ }

mutex_unlock(&b->write_lock);

--
2.20.1