linux-kernel - [v7 PATCH 1/2] mm: vmscan: remove double slab pressure by inc'ing sc->nr

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Date:   Tue, 28 May 2019 14:44:18 +0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     ying.huang@...el.com, hannes@...xchg.org, mhocko@...e.com,
        mgorman@...hsingularity.net, kirill.shutemov@...ux.intel.com,
        josef@...icpanda.com, hughd@...gle.com, shakeelb@...gle.com,
        hdanton@...a.com, akpm@...ux-foundation.org
Cc:     yang.shi@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [v7 PATCH 1/2] mm: vmscan: remove double slab pressure by inc'ing sc->nr_scanned

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@...icpanda.com>
Cc: Michal Hocko <mhocko@...nel.org>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
---
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));
 
-- 
1.8.3.1