netdev - Re: slow performance on disk/network i/o full speed after drop

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Message-ID: <4E5DDE86.3040202@profihost.ag>
Date:	Wed, 31 Aug 2011 09:11:02 +0200
From:	Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>
To:	Zhu Yanhai <zhu.yanhai@...il.com>
CC:	Wu Fengguang <fengguang.wu@...el.com>,
	Pekka Enberg <penberg@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Jens Axboe <jaxboe@...ionio.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: slow performance on disk/network i/o full speed after drop_caches

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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