From: Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 2/3] mm: Ensure that mark_page_accessed moves pages to
 the active list
Date: Mon, 29 Apr 2013 13:12:03 -0400
Message-ID: <517EA9E3.6050407@redhat.com>
References: <1367253119-6461-1-git-send-email-mgorman@suse.de> <1367253119-6461-3-git-send-email-mgorman@suse.de>
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Cc: Alexey Lyahkov <alexey.lyashkov@gmail.com>,
        Andrew Perepechko <anserper@ya.ru>, Robin Dong <sanbai@taobao.com>,
        Theodore Tso <tytso@mit.edu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>, Johannes Weiner <hannes@cmpxchg.org>,
        Bernd Schubert <bernd.schubert@fastmail.fm>,
        David Howells <dhowells@redhat.com>,
        Trond Myklebust <Trond.Myklebust@netapp.com>,
        Linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux-ext4 <linux-ext4@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, Linux-mm <linux-mm@kvack.org>
To: Mel Gorman <mgorman@suse.de>
Return-path: <owner-linux-mm@kvack.org>
In-Reply-To: <1367253119-6461-3-git-send-email-mgorman@suse.de>
Sender: owner-linux-mm@kvack.org
List-Id: linux-ext4.vger.kernel.org

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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