Message-ID: <4BC33A02.8000307@redhat.com>
Date: Mon, 12 Apr 2010 11:19:30 -0400
From: Rik van Riel <riel@redhat.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
       Borislav Petkov <bp@alien8.de>, Johannes Weiner <hannes@cmpxchg.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Minchan Kim <minchan.kim@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Lee Schermerhorn <Lee.Schermerhorn@hp.com>,
       Nick Piggin <npiggin@suse.de>, Andrea Arcangeli <aarcange@redhat.com>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>, sgunderson@bigfoot.com
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas
 of a mergeable VMA
References: <20100409191425.GB10780@a1.tnic>	 <alpine.LFD.2.00.1004091227310.3558@i5.linux-foundation.org>	 <20100409204328.GG28964@cmpxchg.org>	 <alpine.LFD.2.00.1004091546350.3558@i5.linux-foundation.org>	 <alpine.LFD.2.00.1004091638290.3558@i5.linux-foundation.org>	 <20100410003110.GI28964@cmpxchg.org>	 <alpine.LFD.2.00.1004091730130.3558@i5.linux-foundation.org>	 <20100410072714.GA9246@liondog.tnic> <20100410112639.GA24708@a1.tnic>	 <alpine.LFD.2.00.1004100821340.3558@i5.linux-foundation.org>	 <20100410163828.GA25579@a1.tnic>	 <alpine.LFD.2.00.1004100947400.3558@i5.linux-foundation.org>	 <alpine.LFD.2.00.1004101101180.3558@i5.linux-foundation.org> <1271083207.4807.18.camel@twins>
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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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