Commit 9fcc34b1 authored by Coly Li's avatar Coly Li Committed by Jens Axboe

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

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: default avatarColy Li <colyli@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent c5fcdedc
......@@ -754,6 +754,8 @@ 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;
......
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