linux-kernel - Re: [PATCH 1/1] pagemap clear_refs: modify to specify anon or mapped vma clearing

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Date:	Tue, 28 Jul 2009 17:00:54 -0700
From:	Moussa Ba <moussa.a.ba@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, rientjes@...gle.com,
	xiyou.wangcong@...il.com, adobriyan@...il.com, mpm@...enic.com,
	mel@....ul.ie, yinghan@...gle.com, npiggin@...e.de,
	jaredeh@...il.com
Subject: Re: [PATCH 1/1] pagemap clear_refs: modify to specify anon or mapped 
	vma clearing

The patch makes the clear_refs more versatile in adding the option to
select anonymous pages or file backed pages for clearing.  This
addition has a measurable impact on user space application performance
as it decreases the number of pagewalks in scenarios where one is only
interested in a specific type of page (anonymous or file mapped).


On Tue, Jul 28, 2009 at 4:52 PM, Andrew Morton<akpm@...ux-foundation.org> wrote:
> On Tue, 28 Jul 2009 15:52:05 -0700
> "Moussa A. Ba" <moussa.a.ba@...il.com> wrote:
>
>> This patch adds anonymous and file backed filters to the clear_refs interface.
>> echo 1 > /proc/PID/clear_refs resets the bits on all pages
>> echo 2 > /proc/PID/clear_refs resets the bits on anonymous pages only
>> echo 3 > /proc/PID/clear_refs resets the bits on file backed pages only
>> Any other value is ignored
>
> The changelog is missing any rationale for making this change.
> Originally we were told that it "makes the clear_refs proc interface a
> bit more versatile", but that's a bit thin.
>
> How do we justify making this change to Linux?  What value does it
> have?  Can you describe a usage scenario which would help people
> understand the usefulness of the change?
>
> Thanks.
>
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