linux-kernel - Re: [patch 2/3] vmscan: drop page_mapping

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Message-ID: <4B82E8FF.90701@redhat.com>
Date:	Mon, 22 Feb 2010 15:28:47 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/3] vmscan: drop page_mapping_inuse()

On 02/22/2010 02:49 PM, Johannes Weiner wrote:
> page_mapping_inuse() is a historic predicate function for pages that
> are about to be reclaimed or deactivated.
>
> According to it, a page is in use when it is mapped into page tables
> OR part of swap cache OR backing an mmapped file.
>
> This function is used in combination with page_referenced(), which
> checks for young bits in ptes and the page descriptor itself for the
> PG_referenced bit.  Thus, checking for unmapped swap cache pages is
> meaningless as PG_referenced is not set for anonymous pages and
> unmapped pages do not have young ptes.  The test makes no difference.
>
> Protecting file pages that are not by themselves mapped but are part
> of a mapped file is also a historic leftover for short-lived things
> like the exec() code in libc.  However, the VM now does reference
> accounting and activation of pages at unmap time and thus the special
> treatment on reclaim is obsolete.
>
> This patch drops page_mapping_inuse() and switches the two callsites
> to use page_mapped() directly.
>
> Signed-off-by: Johannes Weiner<hannes@...xchg.org>

Reviewed-by: Rik van Riel <riel@...hat.com>

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