From d5c9c470b01177e4d90cdbf178b8c7f37f5b8795 Mon Sep 17 00:00:00 2001 From: Coly Li Date: Fri, 24 Jan 2020 01:01:41 +0800 Subject: [PATCH] bcache: reap c->btree_cache_freeable from the tail in bch_mca_scan() In order to skip the most recently freed btree node cahce, currently in bch_mca_scan() the first 3 caches in c->btree_cache_freeable list are skipped when shrinking bcache node caches in bch_mca_scan(). The related code in bch_mca_scan() is, 737 list_for_each_entry_safe(b, t, &c->btree_cache_freeable, list) { 738 if (nr <= 0) 739 goto out; 740 741 if (++i > 3 && 742 !mca_reap(b, 0, false)) { lines free cache memory 746 } 747 nr--; 748 } The problem is, if virtual memory code calls bch_mca_scan() and the calculated 'nr' is 1 or 2, then in the above loop, nothing will be shunk. In such case, if slub/slab manager calls bch_mca_scan() for many times with small scan number, it does not help to shrink cache memory and just wasts CPU cycles. This patch just selects btree node caches from tail of the c->btree_cache_freeable list, then the newly freed host cache can still be allocated by mca_alloc(), and at least 1 node can be shunk. Signed-off-by: Coly Li Signed-off-by: Jens Axboe --- drivers/md/bcache/btree.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 357535a..c3a314de 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -734,17 +734,17 @@ static unsigned long bch_mca_scan(struct shrinker *shrink, i = 0; btree_cache_used = c->btree_cache_used; - list_for_each_entry_safe(b, t, &c->btree_cache_freeable, list) { + list_for_each_entry_safe_reverse(b, t, &c->btree_cache_freeable, list) { if (nr <= 0) goto out; - if (++i > 3 && - !mca_reap(b, 0, false)) { + if (!mca_reap(b, 0, false)) { mca_data_free(b); rw_unlock(true, b); freed++; } nr--; + i++; } for (; (nr--) && i < btree_cache_used; i++) { -- 2.7.4