[RESEND v5 PATCH 1/2] mm: vmscan: remove double slab pressure by inc'ing sc->nr_scanned

From: Yang Shi
Date: Sun May 26 2019 - 22:01:43 EST

The commit 9092c71bb724 ("mm: use sc->priority for slab shrink targets")
has broken up the relationship between sc->nr_scanned and slab pressure.
The sc->nr_scanned can't double slab pressure anymore. So, it sounds no
sense to still keep sc->nr_scanned inc'ed. Actually, it would prevent
from adding pressure on slab shrink since excessive sc->nr_scanned would
prevent from scan->priority raise.

The bonnie test doesn't show this would change the behavior of
slab shrinkers.

w/ w/o
/sec %CP /sec %CP
Sequential delete: 3960.6 94.6 3997.6 96.2
Random delete: 2518 63.8 2561.6 64.6

The slight increase of "/sec" without the patch would be caused by the
slight increase of CPU usage.

Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
v4: Added Johannes's ack

mm/vmscan.c | 5 -----
1 file changed, 5 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7acd0af..b65bc50 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1137,11 +1137,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
if (!sc->may_unmap && page_mapped(page))
goto keep_locked;

- /* Double the slab pressure for mapped and swapcache pages */
- if ((page_mapped(page) || PageSwapCache(page)) &&
- !(PageAnon(page) && !PageSwapBacked(page)))
- sc->nr_scanned++;
may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));