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

[Moussa Ba <moussa.a.ba@gmail.com>]

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@linux-foundation.org> wrote:
> On Tue, 28 Jul 2009 15:52:05 -0700
> "Moussa A. Ba" <moussa.a.ba@gmail.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.
>