linux-kernel - Re: [PATCHv3] memcg: fix get_scan

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Message-ID: <BANLkTim-U3MTnToFPL11NcVnOCig4zJMAQ@mail.gmail.com>
Date:	Wed, 27 Apr 2011 18:14:56 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Ying Han <yinghan@...gle.com>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"mgorman@...e.de" <mgorman@...e.de>
Subject: Re: [PATCHv3] memcg: fix get_scan_count for small targets

On Wed, Apr 27, 2011 at 5:48 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Wed, 27 Apr 2011 17:48:18 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
>> On Wed, Apr 27, 2011 at 4:47 PM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@...fujitsu.com> wrote:
>> > At memory reclaim, we determine the number of pages to be scanned
>> > per zone as
>> >        (anon + file) >> priority.
>> > Assume
>> >        scan = (anon + file) >> priority.
>> >
>> > If scan < SWAP_CLUSTER_MAX, the scan will be skipped for this time
>> > and priority gets higher. This has some problems.
>> >
>> >  1. This increases priority as 1 without any scan.
>> >     To do scan in this priority, amount of pages should be larger than 512M.
>> >     If pages>>priority < SWAP_CLUSTER_MAX, it's recorded and scan will be
>> >     batched, later. (But we lose 1 priority.)
>> >     If memory size is below 16M, pages >> priority is 0 and no scan in
>> >     DEF_PRIORITY forever.
>> >
>> >  2. If zone->all_unreclaimabe==true, it's scanned only when priority==0.
>> >     So, x86's ZONE_DMA will never be recoverred until the user of pages
>> >     frees memory by itself.
>> >
>> >  3. With memcg, the limit of memory can be small. When using small memcg,
>> >     it gets priority < DEF_PRIORITY-2 very easily and need to call
>> >     wait_iff_congested().
>> >     For doing scan before priorty=9, 64MB of memory should be used.
>> >
>> > Then, this patch tries to scan SWAP_CLUSTER_MAX of pages in force...when
>> >
>> >  1. the target is enough small.
>> >  2. it's kswapd or memcg reclaim.
>> >
>> > Then we can avoid rapid priority drop and may be able to recover
>> > all_unreclaimable in a small zones. And this patch removes nr_saved_scan.
>> > This will allow scanning in this priority even when pages >> priority
>> > is very small.
>> >
>> > Changelog v2->v3
>> >  - removed nr_saved_scan completely.
>> >
>> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>> Reviewed-by: Minchan Kim <minchan.kim@...il.com>
>>
>> The patch looks good to me but I have a nitpick about just coding style.
>> How about this? I think below looks better but it's just my private
>> opinion and I can't insist on my style. If you don't mind it, ignore.
>>
>
> I did this at the 1st try and got bug.....a variable 'file' here is
> reused and now broken. Renaming it with new variable will be ok, but it

Right you are. I missed that. :)
Thanks.


-- 
Kind regards,
Minchan Kim
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