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

[Rik van Riel <riel@redhat.com>]

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@draigBrady.com>
> Signed-off-by: Mel Gorman<mgorman@suse.de>

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

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