linux-kernel - Re: [PATCH] mm: stop kswapd's infinite loop at high order allocation take2

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Date:	Fri, 2 Jan 2009 20:18:57 +0900
From:	"MinChan Kim" <minchan.kim@...il.com>
To:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
Cc:	"Mel Gorman" <mel@....ul.ie>, LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Nick Piggin" <npiggin@...e.de>,
	"wassim dagash" <wassim.dagash@...il.com>
Subject: Re: [PATCH] mm: stop kswapd's infinite loop at high order allocation take2

On Fri, Jan 2, 2009 at 7:54 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>>>> 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.
>

I agree. It can reclaim active pages.
Thanks for kind explain. :)


-- 
Kinds regards,
MinChan Kim
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