Date: Wed, 23 Jun 2004 18:04:01 +0900
From: IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
To: Dave Hansen <haveblue@us.ibm.com>
Cc: Ashwin Rao <ashwin_s_rao@yahoo.com>, Valdis.Kletnieks@vt.edu,
       linux-kernel <linux-kernel@vger.kernel.org>,
       linux-mm <linux-mm@kvack.org>
Subject: Re: Atomic operation for physically moving a page (for memory	defragmentation)
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	<1087619137.4921.93.camel@nighthawk>
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At Fri, 18 Jun 2004 21:25:38 -0700,
Dave Hansen wrote:
> I think what you really want to do is keep anybody else from making a
> new pte to the page, once you've invalidated all of the existing ones,
> right?
> 
> Holding a lock_page() should do the trick.  Anybody that goes any pulls
> the page out of the page cache has to do a lock_page() and check
> page->mapping before they can establish a pte to it, so you can stop
> that.  Since you're invalidating page->mapping before you move the page
> (you *are* doing this, right?), it will end up working itself out.  

This isn't true unless the PG_uptodate bit of the page isn't cleared,
and properly doing that isn't so simple.

I'm planning to post a new version of my memory hotplug patch,
but the page migration code currently doesn't work well with
linux-2.6.7.

--
IWAMOTO Toshihiro

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