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Date: Mon, 22 Feb 2010 12:53:11 -0500
From: Rik van Riel <riel@redhat.com>
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Subject: Re: [patch 25/36] _GFP_NO_KSWAPD
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On 02/21/2010 09:10 AM, aarcange@redhat.com wrote:
> From: Andrea Arcangeli<aarcange@redhat.com>
>
> Transparent hugepage allocations must be allowed not to invoke kswapd or any
> other kind of indirect reclaim (especially when the defrag sysfs is control
> disabled). It's unacceptable to swap out anonymous pages (potentially
> anonymous transparent hugepages) in order to create new transparent hugepages.
> This is true for the MADV_HUGEPAGE areas too (swapping out a kvm virtual
> machine and so having it suffer an unbearable slowdown, so another one with
> guest physical memory marked MADV_HUGEPAGE can run 30% faster if it is running
> memory intensive workloads, makes no sense). If a transparent hugepage
> allocation fails the slowdown is minor and there is total fallback, so kswapd
> should never be asked to swapout memory to allow the high order allocation to
> succeed.
>
> Signed-off-by: Andrea Arcangeli<aarcange@redhat.com>

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

Once Mel's defragmentation code is in, we can kick off
that code instead when a hugepage allocation fails.

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