linux-kernel - Re: [PATCH v3] proc: report file/anon bit in /proc/pid/pagemap

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Date:	Mon, 30 Apr 2012 16:32:40 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Rik van Riel <riel@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Hugh Dickins <hughd@...gle.com>,
	Matt Mackall <mpm@...enic.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3] proc: report file/anon bit in /proc/pid/pagemap

On Mon, Apr 30, 2012 at 6:48 AM, Konstantin Khlebnikov
<khlebnikov@...nvz.org> wrote:
> This is an implementation of Andrew's proposal to extend the pagemap file
> bits to report what is missing about tasks' working set.
>
> The problem with the working set detection is multilateral. In the criu
> (checkpoint/restore) project we dump the tasks' memory into image files
> and to do it properly we need to detect which pages inside mappings are
> really in use. The mincore syscall I though could help with this did not.
> First, it doesn't report swapped pages, thus we cannot find out which
> parts of anonymous mappings to dump. Next, it does report pages from page
> cache as present even if they are not mapped, and it doesn't make
> difference between private pages that has been cow-ed and private pages
> that has not been cow-ed.
>
> Note, that issue with swap pages is critical -- we must dump swap pages to
> image file. But the issues with file pages are optimization -- we can take
> all file pages to image, this would be correct, but if we know that a page
> is not mapped or not cow-ed, we can remove them from dump file. The dump
> would still be self-consistent, though significantly smaller in size (up
> to 10 times smaller on real apps).
>
> Andrew noticed, that the proc pagemap file solved 2 of 3 above issues -- it
> reports whether a page is present or swapped and it doesn't report not
> mapped page cache pages. But, it doesn't distinguish cow-ed file pages from
> not cow-ed.
>
> I would like to make the last unused bit in this file to report whether the
> page mapped into respective pte is PageAnon or not.
>
> [comment stolen from Pavel Emelyanov's v1 patch]
>
> v2:
> * Rebase to uptodate kernel
> * Fix file/anon bit reporting for migration entries
> * Fix frame bits interval comment, it uses 55 lower bits (64 - 3 - 6)
>
> v3:
> * fix stupid misprint s/if/else if/
> * rebase on top of "[PATCH bugfix] proc/pagemap: correctly report non-present
>  ptes and holes between vmas"
> * second patch (with indexes for nonlinear mappings) was droppped.
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> Cc: Pavel Emelyanov <xemul@...allels.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Matt Mackall <mpm@...enic.com>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: KOSAKI Motohiro <kosaki.motohiro@...il.com>

I don't like an exporting naive kernel internal. But unfortunately I
have no alternative idea..
 Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
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