linux-kernel - Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages

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Message-Id: <20100325180846.c6ded3ab.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 25 Mar 2010 18:08:46 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Mel Gorman <mel@....ul.ie>, Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped
 anonymous pages

On Thu, 25 Mar 2010 18:09:34 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> > On Thu, 25 Mar 2010 08:32:35 +0000
> > Mel Gorman <mel@....ul.ie> wrote:

> >  IIUC, the race in memory-hotunplug was fixed by this patch [2/11].
> > 
> >  But, this behavior of unmap_and_move() requires access to _freed_
> >  objects (spinlock). Even if it's safe because of SLAB_DESTROY_BY_RCU,
> >  it't not good habit in general.
> > 
> >  After direct compaction, page-migration will be one of "core" code of
> >  memory management. Then, I agree to patch [1/11] as our direction for
> >  keeping sanity and showing direction to more updates. Maybe adding
> >  refcnt and removing RCU in futuer is good.
> 
> But Christoph seems oppose to remove SLAB_DESTROY_BY_RCU. then refcount
> is meaningless now. I agree you if we will remove SLAB_DESTROY_BY_RCU
> in the future.
> 
removing rcu_read_lock/unlock in unmap_and_move() and removing
SLAB_DESTROY_BY_RCU is different story.

Thanks,
-Kame

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