linux-kernel - Re: [patch 8/8] mm: make per-memcg lru lists exclusive

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Date:	Fri, 3 Jun 2011 00:54:39 +0900
From:	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Ying Han <yinghan@...gle.com>, Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 8/8] mm: make per-memcg lru lists exclusive

2011/6/2 Johannes Weiner <hannes@...xchg.org>:
> On Thu, Jun 02, 2011 at 10:16:59PM +0900, Hiroyuki Kamezawa wrote:
>> 2011/6/1 Johannes Weiner <hannes@...xchg.org>:
>> > All lru list walkers have been converted to operate on per-memcg
>> > lists, the global per-zone lists are no longer required.
>> >
>> > This patch makes the per-memcg lists exclusive and removes the global
>> > lists from memcg-enabled kernels.
>> >
>> > The per-memcg lists now string up page descriptors directly, which
>> > unifies/simplifies the list isolation code of page reclaim as well as
>> > it saves a full double-linked list head for each page in the system.
>> >
>> > At the core of this change is the introduction of the lruvec
>> > structure, an array of all lru list heads.  It exists for each zone
>> > globally, and for each zone per memcg.  All lru list operations are
>> > now done in generic code against lruvecs, with the memcg lru list
>> > primitives only doing accounting and returning the proper lruvec for
>> > the currently scanned memcg on isolation, or for the respective page
>> > on putback.
>> >
>> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
>>
>>
>> could you divide this into
>>   - introduce lruvec
>>   - don't record section? information into pc->flags because we see
>> "page" on memcg LRU
>>     and there is no requirement to get page from "pc".
>>   - remove pc->lru completely
>
> Yes, that makes sense.  It shall be fixed in the next version.
>

BTW, IIUC, Transparent hugepage has a code to link a page to the
page->lru directly.
And recent Minchan's work does the same kind of trick.

But it may put a page onto wrong memcgs if we do link a page to
another page's page->lru
because 2 pages may be in different cgroup each other.

Could you check there are more codes which does link page->lru to nearby page's
page->lru ? Now, I'm not sure there are other codes....but we need care.

Thanks,
-Kame
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