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Date: Mon, 12 Apr 2010 12:06:25 -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>,
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       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>  <4BC33A02.8000307@redhat.com> <1271088103.20295.3383.camel@laptop>
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On 04/12/2010 12:01 PM, Peter Zijlstra wrote:

> @@ -864,15 +889,8 @@ void page_remove_rmap(struct page *page)
>   		__dec_zone_page_state(page, NR_FILE_MAPPED);
>   		mem_cgroup_update_file_mapped(page, -1);
>   	}
> -	/*
> -	 * It would be tidy to reset the PageAnon mapping here,
> -	 * but that might overwrite a racing page_add_anon_rmap
> -	 * which increments mapcount after us but sets mapping
> -	 * before us: so leave the reset to free_hot_cold_page,
> -	 * and remember that it's only reliable while mapped.
> -	 * Leaving it set also helps swapoff to reinstate ptes
> -	 * faster for those pages still in swapcache.
> -	 */
> +
> +	page->mapping = NULL;
>   }

That would be a bug for file pages :)

I could see how it could work for anonymous memory, though.