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

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Date:	Mon, 12 Apr 2010 12:06:25 -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 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.
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