This is a note to let you know that I've just added the patch titled
bcache: at least try to shrink 1 node in bch_mca_scan()
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bcache-at-least-try-to-shrink-1-node-in-bch_mca_scan.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit e5a27fbf90ada632c37af1b4e80234d89349b004
Author: Coly Li <colyli@xxxxxxx>
Date: Wed Nov 13 16:03:24 2019 +0800
bcache: at least try to shrink 1 node in bch_mca_scan()
[ Upstream commit 9fcc34b1a6dd4b8e5337e2b6ef45e428897eca6b ]
In bch_mca_scan(), the number of shrinking btree node is calculated
by code like this,
unsigned long nr = sc->nr_to_scan;
nr /= c->btree_pages;
nr = min_t(unsigned long, nr, mca_can_free(c));
variable sc->nr_to_scan is number of objects (here is bcache B+tree
nodes' number) to shrink, and pointer variable sc is sent from memory
management code as parametr of a callback.
If sc->nr_to_scan is smaller than c->btree_pages, after the above
calculation, variable 'nr' will be 0 and nothing will be shrunk. It is
frequeently observed that only 1 or 2 is set to sc->nr_to_scan and make
nr to be zero. Then bch_mca_scan() will do nothing more then acquiring
and releasing mutex c->bucket_lock.
This patch checkes whether nr is 0 after the above calculation, if 0
is the result then set 1 to variable 'n'. Then at least bch_mca_scan()
will try to shrink a single B+tree node.
Signed-off-by: Coly Li <colyli@xxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 9406326216f1..96a6583e7b52 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -685,6 +685,8 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
* IO can always make forward progress:
*/
nr /= c->btree_pages;
+ if (nr == 0)
+ nr = 1;
nr = min_t(unsigned long, nr, mca_can_free(c));
i = 0;
