linux-kernel - Re: [PATCH 2/2] mm: vmpressure: fix sending wrong events on underflow

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Message-ID: <20170130235834.GC7942@bbox>
Date:   Tue, 31 Jan 2017 08:58:34 +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 2/2] mm: vmpressure: fix sending wrong events on underflow

On Fri, Jan 27, 2017 at 01:43:37PM +0530, Vinayak Menon wrote:
> At the end of a window period, if the reclaimed pages
> is greater than scanned, an unsigned underflow can
> result in a huge pressure value and thus a critical event.
> Reclaimed pages is found to go higher than scanned because
> of the addition of reclaimed slab pages to reclaimed in
> shrink_node without a corresponding increment to scanned
> pages. Minchan Kim mentioned that this can also happen in
> the case of a THP page where the scanned is 1 and reclaimed
> could be 512.
> 
> Signed-off-by: Vinayak Menon <vinmenon@...eaurora.org>
Acked-by: Minchan Kim <minchan@...nel.org>

Thanks for the fix up!