linux-ext4 - Re: [PATCH 2/3] mm: Ensure that mark_page_accessed moves pages to the active list

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Date:	Mon, 29 Apr 2013 13:12:03 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Alexey Lyahkov <alexey.lyashkov@...il.com>,
	Andrew Perepechko <anserper@...ru>,
	Robin Dong <sanbai@...bao.com>, Theodore Tso <tytso@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Bernd Schubert <bernd.schubert@...tmail.fm>,
	David Howells <dhowells@...hat.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux-ext4 <linux-ext4@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 2/3] mm: Ensure that mark_page_accessed moves pages to
 the active list

On 04/29/2013 12:31 PM, Mel Gorman wrote:

> A PageActive page is now added to the inactivate list.
>
> While this looks strange, I think it is sufficiently harmless that additional
> barriers to address the case is not justified.  Unfortunately, while I never
> witnessed it myself, these parallel updates potentially trigger defensive
> DEBUG_VM checks on PageActive and hence they are removed by this patch.

Could this not cause issues with __page_cache_release, called from
munmap, exit, truncate, etc.?

Could the eventual skewing of active vs inactive numbers break page
reclaim heuristics?

I wonder if we would need to move to a scheme where the PG_active bit
is always the authoritive one, and we never pass an overriding "lru"
parameter to __pagevec_lru_add.

Would memory ordering between SetPageLRU and testing for PageLRU be
enough to then prevent the statistics from going off?

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