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Date: Fri, 2 Jan 2009 19:54:34 +0900
From: "KOSAKI Motohiro" <kosaki.motohiro@jp.fujitsu.com>
To: "MinChan Kim" <minchan.kim@gmail.com>
Subject: Re: [PATCH] mm: stop kswapd's infinite loop at high order allocation take2
Cc: "Mel Gorman" <mel@csn.ul.ie>, LKML <linux-kernel@vger.kernel.org>,
       linux-mm <linux-mm@kvack.org>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "Nick Piggin" <npiggin@suse.de>,
       "wassim dagash" <wassim.dagash@gmail.com>
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>>> So I want to balance zone's proportional free page.
>>> How about following ?
>>>
>>> if (nr_reclaimed < SWAP_CLUSTER_MAX) {
>>>   if (order != 0) {
>>>     order -=1;
>>>     sc.order -=1;
>>>   }
>>> }
>>>
>>> It prevents infinite loop and do best effort to make zone's
>>> proportional free page per order size good.
>>>
>>> It's just my opinion within my knowledge.
>>> If it have a problem, pz, explain me :)
>>
>> Please read Nick's expalin. it explain very kindly :)
>
> Hm. I read Nick's explain.
> I understand his point.
>
> Nick said,
> "A higher kswapd reclaim order shouldn't weaken kswapd
> postcondition for order-0 memory."
>
> My patch don't prevent order-0 memory reclaim. After all, it will do it.
> It also can do best effort to reclaim other order size.
>
> In this case, others order size reclaim is needless  ?

Yes, needless.

wakeup_kswapd() function mean
  - please make free memory until pages_high
  - and, I want to "order argument" conteniously pages.

then, shorter conteniously pages than "order argumet" pages aren't needed
by caller.

Unfortunately, your patch has more bad side effect.
high order shrink_zone() cause lumpy reclaim.
lumpy reclaim cause reclaim neighbor pages although it is active page.

needlessly active page reclaiming decrease system performance.