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Date: Wed, 31 Aug 2011 09:11:02 +0200
From: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
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Subject: Re: slow performance on disk/network i/o full speed after drop_caches
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Sender: owner-linux-mm@kvack.org
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To: Zhu Yanhai <zhu.yanhai@gmail.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>, Pekka Enberg <penberg@kernel.org>, LKML <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mel@csn.ul.ie>, Jens Axboe <jaxboe@fusionio.com>, Linux Netdev List <netdev@vger.kernel.org>

Hi Fengguang,
Hi Yanhai,

> you're abssolutely corect zone_reclaim_mode is on - but why?
> There must be some linux software which switches it on.
>
> ~# grep 'zone_reclaim_mode' /etc/sysctl.* -r -i
> ~#
>
> also
> ~# grep 'zone_reclaim_mode' /etc/sysctl.* -r -i
> ~#
>
> tells us nothing.
>
> I've then read this:
>
> "zone_reclaim_mode is set during bootup to 1 if it is determined that
> pages from remote zones will cause a measurable performance reduction.
> The page allocator will then reclaim easily reusable pages (those page
> cache pages that are currently not used) before allocating off node pages."
>
> Why does the kernel do that here in our case on these machines.

Can nobody help why the kernel in this case set it to 1?

Stefan

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