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

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Date:	Thu, 29 Dec 2011 14:31:20 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Hugh Dickins <hughd@...gle.com>, Minchan Kim <minchan@...nel.org>,
	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>,
	Johannes Weiner <jweiner@...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 12/29/2011 11:59 AM, Mel Gorman wrote:

> I considered a few ways of fixing this. The obvious one is to add a
> new page flag but that is difficult to justify as the high-cpu-usage
> problem should only occur when there is a lot of writeback to slow
> storage which I believe is a rare case. It is not a suitable use for
> an extended page flag.

Actually, don't we already have three LRU related
bits in the page flags?

We could stop using those as bit flags, and use
them as a number instead. That way we could encode
up to 7 or 8 (depending on how we use all-zeroes)
LRU lists with the number of bits we have now.

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