linux-kernel - Re: [patch 3/9] Guest page hinting: volatile page cache.

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Date:	Fri, 01 Sep 2006 11:23:44 -0700
From:	Dave Hansen <haveblue@...ibm.com>
To:	schwidefsky@...ibm.com
Cc:	Andy Whitcroft <apw@...dowen.org>, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, akpm@...l.org,
	nickpiggin@...oo.com.au, frankeh@...son.ibm.com
Subject: Re: [patch 3/9] Guest page hinting: volatile page cache.

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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