linux-kernel - Re: Interaction between Xen and XFS: stray RW mappings

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Date:	Tue, 23 Oct 2007 11:28:38 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	David Chinner <dgc@....com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	dean gaudet <dean@...tic.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Xen-devel <xen-devel@...ts.xensource.com>, Morten@...e.de,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Bøgeskov <xen-users@...ten.bogeskov.dk>,
	xfs@....sgi.com, xfs-masters@....sgi.com,
	Mark Williamson <mark.williamson@...cam.ac.uk>
Subject: Re: Interaction between Xen and XFS: stray RW mappings

On Tue, Oct 23, 2007 at 10:36:41AM +1000, David Chinner wrote:
> > That doesn't mean it is correct.
> 
> Right, but it also points to the fact that it's not causing problems
> from 99.999% of ppl out there.

So you're waiting for someone to take months to debug this again? 

> You mean like vmap() could record the pages passed to it in the area->pages
> array, 

The page tables contain pointers to the pages anyways. vunmap() has to walk 
them.  It would not be very difficult to store them in an array during
the walk.

> 
> If we did this, it would probably be best to pass a page release function
> into the vmap or vunmap call - we'd need page_cache_release() called on
> the page rather than __free_page()....

Possible. Normally vmalloc pages should not be in the LRU except yours
so it would be probably fine to just change it.

> The solution belongs behind the vmap/vunmap interface, not in XFS....

You could also just keep the array from map time around yourself. 
Then you could do it yourself.

-Andi
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