linux-kernel - Re: [PATCH 2/4] Add replace_page(), change the mapping of pte from one page into another

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Date:	Wed, 12 Nov 2008 14:27:42 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <ieidus@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kvm@...r.kernel.org, chrisw@...hat.com,
	avi@...hat.com, izike@...ranet.com
Subject: Re: [PATCH 2/4] Add replace_page(), change the mapping of pte from
 one page into another

On Wed, 12 Nov 2008, Andrea Arcangeli wrote:

> On Tue, Nov 11, 2008 at 09:10:45PM -0600, Christoph Lameter wrote:
> > get_user_pages() cannot get to it since the pagetables have already been
> > modified. If get_user_pages runs then the fault handling will occur
> > which will block the thread until migration is complete.
>
> migrate.c does nothing for ptes pointing to swap entries and
> do_swap_page won't wait for them either. Assume follow_page in

If a anonymous page is a swap page then it has a mapping.
migrate_page_move_mapping() will lock the radix tree and ensure that no
additional reference (like done by do_swap_page) is established during
migration.

> However it's not exactly the same bug as the one in fork, I was
> talking about before, it's also not o_direct specific. Still

So far I have seen wild ideas not bugs.



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