From 9fcc34b1a6dd4b8e5337e2b6ef45e428897eca6b Mon Sep 17 00:00:00 2001 From: Coly Li Date: Wed, 13 Nov 2019 16:03:24 +0800 Subject: [PATCH] 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: Coly Li Signed-off-by: Jens Axboe --- drivers/md/bcache/btree.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 48e33ee0d876..3df5fa4a501c 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -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;