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

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Message-Id: <20110501222117.75E8.A69D9226@jp.fujitsu.com>
Date:	Sun,  1 May 2011 22:19:45 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, Mel Gorman <mgorman@...e.de>,
	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>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC 5/8] compaction: remove active list counting

> On Thu, Apr 28, 2011 at 7:50 PM, Mel Gorman <mgorman@...e.de> wrote:
> > 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.
> 
> True.
> 
> >
> > 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.
> 
> When Kame pointed out comment, I wanted to avoid unnecessary comment
> so decided changing it with page_lru although it adds overhead a
> little bit. But Hannes, you and maybe Kame don't want it. I don't mind
> adding comment.
> Okay. fix it in next version.

Or

	unsigned int count[2];

        list_for_each_entry(page, &cc->migratepages, lru) {
                count[page_is_file_cache(page)]++;
        }

is also clear to me.


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