linux-kernel - Re: [PATCH v2] vmscan: reverse lru scanning order

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Date:	Tue, 9 Aug 2011 07:30:48 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Konstantin Khlebnikov <khlebnikov@...nvz.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH v2] vmscan: reverse lru scanning order

On Mon, Aug 8, 2011 at 9:22 PM, Michal Hocko <mhocko@...e.cz> wrote:
> On Mon 08-08-11 15:02:07, Konstantin Khlebnikov wrote:
>> LRU scanning order was accidentially changed in commit v2.6.27-5584-gb69408e:
>> "vmscan: Use an indexed array for LRU variables".
>> Before that commit reclaimer always scan active lists first.
>>
>> This patch just reverse it back.
>
> I am still not sure I see why the ordering matters that much.
> One thing that might matter is that shrink_list moves some pages from
> active to inactive list if inactive is low so it makes sense to try to
> shrink active before inactive. It would be a problem if inactive was
> almost empty. Then we would just waste time by shrinking inactive first.
> I am not sure how real problem is that, though.
>
> Whatever is the reason, I think it should be documented in the
> changelog.
> The change makes sense to me.
>

Absolutely agree with Michal.
I think the patch itself doesn't have a problem and even it is does make sense.
But we need changelog why we need it.
I don't want to overwrite recent git log without any issue.
It annoys us when we find a bug by git-blame. ;-)
-- 
Kind regards,
Minchan Kim
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