linux-kernel - Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure

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Date:   Wed, 1 Feb 2017 15:12:48 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Vinayak Menon <vinmenon@...eaurora.org>
CC:     <akpm@...ux-foundation.org>, <hannes@...xchg.org>,
        <mgorman@...hsingularity.net>, <vbabka@...e.cz>, <mhocko@...e.com>,
        <riel@...hat.com>, <vdavydov.dev@...il.com>,
        <anton.vorontsov@...aro.org>, <shashim@...eaurora.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to
 vmpressure

On Tue, Jan 31, 2017 at 02:32:08PM +0530, Vinayak Menon wrote:
> During global reclaim, the nr_reclaimed passed to vmpressure
> includes the pages reclaimed from slab. But the corresponding
> scanned slab pages is not passed. This can cause total reclaimed
> pages to be greater than scanned, causing an unsigned underflow
> in vmpressure resulting in a critical event being sent to root
> cgroup. So do not consider reclaimed slab pages for vmpressure
> calculation. The reclaimed pages from slab can be excluded because
> the freeing of a page by slab shrinking depends on each slab's
> object population, making the cost model (i.e. scan:free) different
> from that of LRU. Also, not every shrinker accounts the pages it
> reclaims. This is a regression introduced by commit 6b4f7799c6a5
> ("mm: vmscan: invoke slab shrinkers from shrink_zone()").
> 
> Signed-off-by: Vinayak Menon <vinmenon@...eaurora.org>
Acked-by: Minchan Kim <minchan@...nel.org>