linux-kernel - Re: [PATCH 2/4] mm: vmscan: Do not apply pressure to slab if we are not applying pressure to zone

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Date:	Sat, 25 Jun 2011 17:40:24 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Pádraig Brady <P@...igBrady.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Colin King <colin.king@...onical.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Lutomirski <luto@....edu>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] mm: vmscan: Do not apply pressure to slab if we are
 not applying pressure to zone

On 06/24/2011 10:44 AM, Mel Gorman wrote:
> During allocator-intensive workloads, kswapd will be woken frequently
> causing free memory to oscillate between the high and min watermark.
> This is expected behaviour.
>
> When kswapd applies pressure to zones during node balancing, it checks
> if the zone is above a high+balance_gap threshold. If it is, it does
> not apply pressure but it unconditionally shrinks slab on a global
> basis which is excessive. In the event kswapd is being kept awake due to
> a high small unreclaimable zone, it skips zone shrinking but still
> calls shrink_slab().
>
> Once pressure has been applied, the check for zone being unreclaimable
> is being made before the check is made if all_unreclaimable should be
> set. This miss of unreclaimable can cause has_under_min_watermark_zone
> to be set due to an unreclaimable zone preventing kswapd backing off
> on congestion_wait().
>
> Reported-and-tested-by: Pádraig Brady<P@...igBrady.com>
> Signed-off-by: Mel Gorman<mgorman@...e.de>

Acked-by: Rik van Riel <riel@...hat.com>

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