linux-kernel - Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon

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Message-ID: <4BC33A02.8000307@redhat.com>
Date:	Mon, 12 Apr 2010 11:19:30 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas
 of a mergeable VMA

On 04/12/2010 10:40 AM, Peter Zijlstra wrote:

> So the reason page->mapping isn't cleared in page_remove_rmap() isn't
> detailed beyond a (possible) race with page_add_anon_rmap() (which I
> guess would be reclaim trying to unmap the page and a fault re-instating
> it).
>
> This also complicates the whole page_lock_anon_vma() thing, so it would
> be nice to be able to remove this race and clear page->mapping in
> page_remove_rmap().

For anonymous pages, I don't see where the race comes from.

Both do_swap_page and the reclaim code hold the page lock
across the entire operation, so they are already excluding
each other.

Hugh, do you remember what the race between page_remove_rmap
and page_add_anon_rmap is/was all about?

I don't see a race in the current code...
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