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

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Date:	Mon, 2 May 2011 00:09:26 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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 Sun, May 1, 2011 at 10:19 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> 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.
>

That's very clear to me, too.
Thanks, KOSAKI.



-- 
Kind regards,
Minchan Kim
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