Subject: Re: [patch 3/9] Guest page hinting: volatile page cache.
From: Dave Hansen <haveblue@us.ibm.com>
To: schwidefsky@de.ibm.com
Cc: Andy Whitcroft <apw@shadowen.org>, linux-kernel@vger.kernel.org,
       virtualization@lists.osdl.org, akpm@osdl.org, nickpiggin@yahoo.com.au,
       frankeh@watson.ibm.com
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Date: Fri, 01 Sep 2006 11:23:44 -0700
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On Fri, 2006-09-01 at 20:04 +0200, Martin Schwidefsky wrote:
> On Fri, 2006-09-01 at 11:03 -0700, Dave Hansen wrote:
> > OK.  It comes down to a race between 
> > 
> >         __remove_from_page_cache()/__delete_from_swap_cache()
> > 
> > and
> > 
> >         __page_discard()
> > 
> > running on the same page at the same time.  Right?
> 
> Yes.

OK, and there's no other workable solution to exclude each other from
running at the same time than a bit in page->flags?

It seems like that hashed lock (or lock in mem_map[]) we were talking
about earlier might be applicable here, too.

Do we ever discard pages other than ones that have just recently failed
to be made stable?  There seems to be a lot of

	if (!page_make_stable(page) {
		...
		page_discard(page);
	}

Some of these call sites even have mapping->page_lock held when the
page_make_stable() occurs, so they would have _already_ excluded
__remove_from_page_cache().  At which call sites is it not feasible to
acquire mapping->page_lock?

-- Dave

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