linux-kernel - Re: [v3 PATCH 1/2] mm: vmscan: remove double slab pressure by inc'ing sc->nr

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Date:   Tue, 21 May 2019 11:45:48 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     ying.huang@...el.com, mhocko@...e.com, mgorman@...hsingularity.net,
        kirill.shutemov@...ux.intel.com, josef@...icpanda.com,
        hughd@...gle.com, shakeelb@...gle.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v3 PATCH 1/2] mm: vmscan: remove double slab pressure by
 inc'ing sc->nr_scanned

On Tue, May 21, 2019 at 05:40:41PM +0800, Yang Shi wrote:
> 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>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>