iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

bcache: at least try to shrink 1 node in bch_mca_scan()

Browse Source 
[ 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@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Coly Li 2019-11-13 16:03:24 +08:00 committed by Greg Kroah-Hartman
parent 0884d8df84
commit 90cfabd5f3
1 changed files with 2 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/md/bcache/btree.c
View File

@ -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;