linux-kernel - Re: [PATCH] mm: vmpressure: fix scan window after SWAP_CLUSTER

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Message-ID: <20151021193852.GA13511@cmpxchg.org>
Date:	Wed, 21 Oct 2015 15:38:52 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vladimir Davydov <vdavydov@...tuozzo.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: vmpressure: fix scan window after SWAP_CLUSTER_MAX
 increase

On Mon, Oct 19, 2015 at 02:13:01PM -0400, Johannes Weiner wrote:
> mm-increase-swap_cluster_max-to-batch-tlb-flushes.patch changed
> SWAP_CLUSTER_MAX from 32 pages to 256 pages, inadvertantly switching
> the scan window for vmpressure detection from 2MB to 16MB. Revert.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> ---
>  mm/vmpressure.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index c5afd57..74f206b 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -38,7 +38,7 @@
>   * TODO: Make the window size depend on machine size, as we do for vmstat
>   * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
>   */
> -static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
> +static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX;

Argh, Mel's patch sets SWAP_CLUSTER_MAX to 256, so this should be
SWAP_CLUSTER_MAX * 2 to retain the 512 pages scan window.

Andrew could you please update this fix in-place? Otherwise I'll
resend a corrected version.

Thanks, and sorry about that.
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