From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Fri, 25 Apr 2008 09:11:35 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: Warning on memory offline (and possible in usual migration?)
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To: Christoph Lameter <clameter@sgi.com>
Cc: Nick Piggin <npiggin@suse.de>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, GOTO <y-goto@jp.fujitsu.com>
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On Thu, 24 Apr 2008 12:11:07 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:

> On Thu, 24 Apr 2008, KAMEZAWA Hiroyuki wrote:
> 
> > > So its safe to migrate a !Uptodate page if it contains buffers? Note that 
> > > the migration code reattaches the buffer to the new page in 
> > > buffer_migrate_page().
> > > 
> > I think it's safe because it reattaches buffers as you explained.
> > 
> > under migration
> > 1. a page is locked.
> > 2. buffers are reattached.
> > 3. a PG_writeback page are not migrated.
> > 
> > So, it seems safe.
> 
> Concurrent DMA reads cannot occur while we migrate? What holds off 
> potential I/O to the page? The page lock? Or some buffer lock?
> 
> Not that the "buffers" are segments of the page that is migrated.
> If concurrent transfers occur while we copy the page then we may see data 
> corruption.
> 
Hmm ? If a buffer in a page is under I/O, the whole page is locked, isn't it ?
If not, It seems anyone cannot use a page safely.

Thanks,
-Kame

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