linux-kernel - Re: [PATCH 11/11] mm: Isolate pages for immediate reclaim on their own LRU

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Date:	Fri, 16 Dec 2011 16:17:31 +0100
From:	Johannes Weiner <jweiner@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Dave Jones <davej@...hat.com>, Jan Kara <jack@...e.cz>,
	Andy Isaacson <adi@...apodia.org>,
	Rik van Riel <riel@...hat.com>, Nai Xia <nai.xia@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/11] mm: Isolate pages for immediate reclaim on their
 own LRU

On Wed, Dec 14, 2011 at 03:41:33PM +0000, Mel Gorman wrote:
> It was observed that scan rates from direct reclaim during tests
> writing to both fast and slow storage were extraordinarily high. The
> problem was that while pages were being marked for immediate reclaim
> when writeback completed, the same pages were being encountered over
> and over again during LRU scanning.
> 
> This patch isolates file-backed pages that are to be reclaimed when
> clean on their own LRU list.

Excuse me if I sound like a broken record, but have those observations
of high scan rates persisted with the per-zone dirty limits patchset?

In my tests with pzd, the scan rates went down considerably together
with the immediate reclaim / vmscan writes.

Our dirty limits are pretty low - if reclaim keeps shuffling through
dirty pages, where are the 80% reclaimable pages?!  To me, this sounds
like the unfair distribution of dirty pages among zones again.  Is
there are a different explanation that I missed?

PS: It also seems a bit out of place in this series...?
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