linux-kernel - Re: [PATCH 2/3] check unevictable flag in lumy reclaim v2

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Date:	Thu, 11 Jun 2009 20:19:45 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	"Minchan Kim" <minchan.kim@...il.com>
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	apw@...onical.com, riel@...hat.com, mel@....ul.ie
Subject: Re: [PATCH 2/3] check unevictable flag in lumy reclaim v2

Minchan Kim さん wrote:
> On Thu, Jun 11, 2009 at 5:38 PM, KAMEZAWA
> Hiroyuki<kamezawa.hiroyu@...fujitsu.com> wrote:
>> How about this ?
>>
>> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>>
>> Lumpy reclaim check pages from their pfn. Then, it can find unevictable
>> pages
>> in its loop.
>> Abort lumpy reclaim when we find Unevictable page, we never get a lump
>> of pages for requested order.
>>
>> Changelog: v1->v2
>> ?- rewrote commet.
>>
>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>> ---
>> ?mm/vmscan.c | ? ?9 +++++++++
>> ?1 file changed, 9 insertions(+)
>>
>> Index: lumpy-reclaim-trial/mm/vmscan.c
>> ===================================================================
>> --- lumpy-reclaim-trial.orig/mm/vmscan.c
>> +++ lumpy-reclaim-trial/mm/vmscan.c
>> @@ -936,6 +936,15 @@ static unsigned long isolate_lru_pages(u
>> ? ? ? ? ? ? ? ? ? ? ? ?/* Check that we have not crossed a zone
>> boundary. */
>> ? ? ? ? ? ? ? ? ? ? ? ?if (unlikely(page_zone_id(cursor_page) !=
>> zone_id))
>> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?continue;
>> + ? ? ? ? ? ? ? ? ? ? ? /*
>> + ? ? ? ? ? ? ? ? ? ? ? ?* We tries to free all pages in this range to
>> create
>> + ? ? ? ? ? ? ? ? ? ? ? ?* a free large page. Then, if the range
>> includes a page
>> + ? ? ? ? ? ? ? ? ? ? ? ?* never be reclaimed, we have no reason to do
>> more.
>> + ? ? ? ? ? ? ? ? ? ? ? ?* PageUnevictable page is not a page which can
>> be
>> + ? ? ? ? ? ? ? ? ? ? ? ?* easily freed. Abort this scan now.
>> + ? ? ? ? ? ? ? ? ? ? ? ?*/
>> + ? ? ? ? ? ? ? ? ? ? ? if (unlikely(PageUnevictable(cursor_page)))
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? break;
>
> __isolate_lru_pages already checked PageUnevictable to return error.
> I want to remove repeated check although it is trivial.
>
> By your patch, It seems to remove PageUnevictable check in
> __isolate_lru_pages.
>
yes.

> But I know that. If we remove PageUnevictable check in
> __isolate_lru_pages, it can't go into BUG in non-lumpy case. ( I
> mentioned following as code)
>
In non-lumpy case, we'll never see Unevictable, maybe.

>                 case -EBUSY:
>                         /* else it is being freed elsewhere */
>                         list_move(&page->lru, src);
>                         continue;
>
>                 default:
>                         BUG();
>                 }
>
>
> It means we can remove BUG in non-lumpy case and then add BUG into
> __isolate_lru_pages directly.
>
> If we can do it, we can remove unnecessary PageUnevictable check in
> __isolate_lru_page.
>
Hmm, but Unevicable check had tons of troubles at its implementation
and I don't want to do it at once.

> I am not sure this is right in case of memcg.
>
I think we don't see Unevictable in memcg's path if my memcg-lru code
works as designed.

I'll postpone this patch for a while until my brain works well.

Thanks,
-Kame

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