From: Swamy Gowda <swamy@virident.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>,
linux-kernel@vger.kernel.org, Brice.Goglin@inria.fr,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [RFC][PATCH] release mmap_sem before starting migration (Was Re: Need to take mmap_sem lock in move_pages.
Date: Thu, 05 Feb 2009 17:53:57 +0530 [thread overview]
Message-ID: <498ADA5D.90201@virident.com> (raw)
In-Reply-To: <20090205101503.b1fd7df6.kamezawa.hiroyu@jp.fujitsu.com>
KAMEZAWA Hiroyuki wrote:
> On Wed, 4 Feb 2009 10:39:19 -0500 (EST)
> Christoph Lameter <cl@linux-foundation.org> wrote:
>
>> On Wed, 4 Feb 2009, KAMEZAWA Hiroyuki wrote:
>>
>> > mmap_sem can be released after page table walk ends.
>>
>> No. read lock on mmap_sem must be held since the migrate functions
>> manipulate page table entries. Concurrent large scale changes to the
>> page
>> tables (splitting vmas, remapping etc) must not be possible.
>>
> Just for clarification:
>
> 1. changes in page table is not problem from the viewpoint of kernel.
> (means no panic, no leak,...)
> 2. But this loses "atomic" aspect of migration and will allow unexpected
> behaviors.
> (means the page-mapping status after sys_move may not be what user
> expects.)
>
>
> Thanks,
> -Kame
>
>
But I can't understand how user can see different page->mapping , since
new page->mapping still holds the anon_vma pointer which should still
contain the changes in the vma list( due to split vma etc). But,
considering it as a problem how is it avoided in case of hotremove?
--Swamy
WARNING: multiple messages have this Message-ID (diff)
From: Swamy Gowda <swamy@virident.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>,
linux-kernel@vger.kernel.org, Brice.Goglin@inria.fr,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [RFC][PATCH] release mmap_sem before starting migration (Was Re: Need to take mmap_sem lock in move_pages.
Date: Thu, 05 Feb 2009 17:53:57 +0530 [thread overview]
Message-ID: <498ADA5D.90201@virident.com> (raw)
In-Reply-To: <20090205101503.b1fd7df6.kamezawa.hiroyu@jp.fujitsu.com>
KAMEZAWA Hiroyuki wrote:
> On Wed, 4 Feb 2009 10:39:19 -0500 (EST)
> Christoph Lameter <cl@linux-foundation.org> wrote:
>
>> On Wed, 4 Feb 2009, KAMEZAWA Hiroyuki wrote:
>>
>> > mmap_sem can be released after page table walk ends.
>>
>> No. read lock on mmap_sem must be held since the migrate functions
>> manipulate page table entries. Concurrent large scale changes to the
>> page
>> tables (splitting vmas, remapping etc) must not be possible.
>>
> Just for clarification:
>
> 1. changes in page table is not problem from the viewpoint of kernel.
> (means no panic, no leak,...)
> 2. But this loses "atomic" aspect of migration and will allow unexpected
> behaviors.
> (means the page-mapping status after sys_move may not be what user
> expects.)
>
>
> Thanks,
> -Kame
>
>
But I can't understand how user can see different page->mapping , since
new page->mapping still holds the anon_vma pointer which should still
contain the changes in the vma list( due to split vma etc). But,
considering it as a problem how is it avoided in case of hotremove?
--Swamy
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next prev parent reply other threads:[~2009-02-05 12:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <28631E6913C8074E95A698E8AC93D091B21561@caexch1.virident.info>
2009-02-04 9:36 ` Need to take mmap_sem lock in move_pages KAMEZAWA Hiroyuki
2009-02-04 9:40 ` KAMEZAWA Hiroyuki
2009-02-04 9:55 ` [RFC][PATCH] release mmap_sem before starting migration (Was " KAMEZAWA Hiroyuki
2009-02-04 9:55 ` KAMEZAWA Hiroyuki
2009-02-04 15:39 ` Christoph Lameter
2009-02-04 15:39 ` Christoph Lameter
2009-02-05 1:15 ` KAMEZAWA Hiroyuki
2009-02-05 1:15 ` KAMEZAWA Hiroyuki
2009-02-05 12:23 ` Swamy Gowda [this message]
2009-02-05 12:23 ` Swamy Gowda
2009-02-05 13:23 ` KAMEZAWA Hiroyuki
2009-02-05 13:23 ` KAMEZAWA Hiroyuki
2009-02-04 15:34 ` Christoph Lameter
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