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From:   Yang Shi <yang.shi@linux.alibaba.com>
To:     ying.huang@intel.com, hannes@cmpxchg.org, mhocko@suse.com,
        mgorman@techsingularity.net, kirill.shutemov@linux.intel.com,
        josef@toxicpanda.com, hughd@google.com, shakeelb@google.com,
        akpm@linux-foundation.org
Cc:     yang.shi@linux.alibaba.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [v3 PATCH 1/2] mm: vmscan: remove double slab pressure by inc'ing sc->nr_scanned
Date:   Tue, 21 May 2019 17:40:41 +0800
Message-Id: <1558431642-52120-1-git-send-email-yang.shi@linux.alibaba.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@toxicpanda.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
 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