linux-kernel - Re: [PATCH -mm] change anon_vma linking to fix multi-process server scalability issue

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Date:	Thu, 11 Feb 2010 16:49:35 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"Luck, Tony" <tony.luck@...el.com>,
	Linux kernel Mailing List <linux-kernel@...r.kernel.org>,
	shak <dshaks@...hat.com>
Subject: Re: [PATCH -mm] change anon_vma linking to fix multi-process server
 scalability issue

On 02/11/2010 04:04 PM, Andrew Morton wrote:
> On Thu, 28 Jan 2010 00:20:00 -0500
> Rik van Riel<riel@...hat.com>  wrote:
>
>> The old anon_vma code can lead to scalability issues with heavily
>> forking workloads.  Specifically, each anon_vma will be shared
>> between the parent process and all its child processes.

Some test results:

Without the anon_vma changes, when AIM7 hits around 9.7k
users (on a test box with 16GB RAM and not quite enough IO),
the system ends up running >99% in system time, with every
CPU on the same anon_vma lock in the pageout code.

With these changes, AIM7 hits the cross-over point around
29.7k users.  This happens with ~99% IO wait time, there
never seems to be any spike in system time.  The anon_vma
lock contention appears to be resolved.

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