linux-kernel - Re: [PATCH v2] fadvise: move active pages to inactive list with POSIX_FADV

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Message-Id: <E03B7391-C7D0-4EBE-96FE-C7537F9E353B@mit.edu>
Date:	Thu, 23 Jun 2011 08:10:47 -0400
From:	Theodore Tso <tytso@....EDU>
To:	Andrea Righi <andrea@...terlinux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Jerry James <jamesjer@...terlinux.com>,
	Marcus Sorensen <marcus@...ehost.com>,
	Matt Heaton <matt@...ehost.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] fadvise: move active pages to inactive list with POSIX_FADV_DONTNEED

On Jun 23, 2011, at 2:36 AM, Andrea Righi wrote:

> 
> With the following solution when posix_fadvise(POSIX_FADV_DONTNEED) is
> called for an active page instead of removing it from the page cache it
> is added to the tail of the inactive list. Otherwise, if it's already in
> the inactive list the page is removed from the page cache.

Have you thought about this heuristic?   If the page is active, try to
remove it from the current process's page table.  If that drops the
use count of the page to zero, then drop it from the page cache;
otherwise, leave it alone.

That way, if the page is being used by anyone else, we don't touch
the page at all.   fadvise() should only affect the current process; if
it's available to non-root users, it shouldn't be affecting other
processes, and if it is being actively used by some other process,
removing it from their page tables so it can be put on the inactive
list counts as interference, doesn't it?

-- Ted

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