linux-kernel - Re: [RFC 5/8] compaction: remove active list counting

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Message-ID: <20110428105027.GT4658@suse.de>
Date:	Thu, 28 Apr 2011 11:50:27 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC 5/8] compaction: remove active list counting

On Wed, Apr 27, 2011 at 01:25:22AM +0900, Minchan Kim wrote:
> acct_isolated of compaction uses page_lru_base_type which returns only
> base type of LRU list so it never returns LRU_ACTIVE_ANON or LRU_ACTIVE_FILE.
> So it's pointless to add lru[LRU_ACTIVE_[ANON|FILE]] to get sum.
> 
> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Signed-off-by: Minchan Kim <minchan.kim@...il.com>

hmm, isolate_migratepages() is doing a linear scan of PFNs and is
calling __isolate_lru_page(..ISOLATE_BOTH..). Using page_lru_base_type
happens to work because we're only interested in the number of isolated
pages and your patch still covers that. Using page_lru might be more
accurate in terms of accountancy but does not seem necessary.

Adding a comment explaining why we account for it as inactive and why
that's ok would be nice although I admit this is something I should have
done when acct_isolated() was introduced.

-- 
Mel Gorman
SUSE Labs
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