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Date: Tue, 20 May 2008 07:31:46 +0200 From: Nick Piggin <npiggin@...e.de> To: Robin Holt <holt@....com> Cc: Christoph Lameter <clameter@....com>, Nick Piggin <nickpiggin@...oo.com.au>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrea Arcangeli <andrea@...ranet.com>, Andrew Morton <akpm@...ux-foundation.org>, Jack Steiner <steiner@....com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, kvm-devel@...ts.sourceforge.net, Kanoj Sarcar <kanojsarcar@...oo.com>, Roland Dreier <rdreier@...co.com>, Steve Wise <swise@...ngridcomputing.com>, linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>, linux-mm@...ck.org, general@...ts.openfabrics.org, Hugh Dickins <hugh@...itas.com>, Rusty Russell <rusty@...tcorp.com.au>, Anthony Liguori <aliguori@...ibm.com>, Chris Wright <chrisw@...hat.com>, Marcelo Tosatti <marcelo@...ck.org>, Eric Dumazet <dada1@...mosbay.com>, "Paul E. McKenney" <paulmck@...ibm.com> Subject: Re: [PATCH 08 of 11] anon-vma-rwsem On Fri, May 16, 2008 at 06:50:05AM -0500, Robin Holt wrote: > On Fri, May 16, 2008 at 06:23:06AM -0500, Robin Holt wrote: > > On Fri, May 16, 2008 at 01:52:03AM +0200, Nick Piggin wrote: > > > On Thu, May 15, 2008 at 10:33:57AM -0700, Christoph Lameter wrote: > > > > On Thu, 15 May 2008, Nick Piggin wrote: > > > > > > > > > Oh, I get that confused because of the mixed up naming conventions > > > > > there: unmap_page_range should actually be called zap_page_range. But > > > > > at any rate, yes we can easily zap pagetables without holding mmap_sem. > > > > > > > > How is that synchronized with code that walks the same pagetable. These > > > > walks may not hold mmap_sem either. I would expect that one could only > > > > remove a portion of the pagetable where we have some sort of guarantee > > > > that no accesses occur. So the removal of the vma prior ensures that? > > > > > > I don't really understand the question. If you remove the pte and invalidate > > > the TLBS on the remote image's process (importing the page), then it can > > > of course try to refault the page in because it's vma is still there. But > > > you catch that refault in your driver , which can prevent the page from > > > being faulted back in. > > > > I think Christoph's question has more to do with faults that are > > in flight. A recently requested fault could have just released the > > last lock that was holding up the invalidate callout. It would then > > begin messaging back the response PFN which could still be in flight. > > The invalidate callout would then fire and do the interrupt shoot-down > > while that response was still active (essentially beating the inflight > > response). The invalidate would clear up nothing and then the response > > would insert the PFN after it is no longer the correct PFN. > > I just looked over XPMEM. I think we could make this work. We already > have a list of active faults which is protected by a simple spinlock. > I would need to nest this lock within another lock protected our PFN > table (currently it is a mutex) and then the invalidate interrupt handler > would need to mark the fault as invalid (which is also currently there). > > I think my sticking points with the interrupt method remain at fault > containment and timeout. The inability of the ia64 processor to handle > provide predictive failures for the read/write of memory on other > partitions prevents us from being able to contain the failure. I don't > think we can get the information we would need to do the invalidate > without introducing fault containment issues which has been a continous > area of concern for our customers. Really? You can get the information through via a sleeping messaging API, but not a non-sleeping one? What is the difference from the hardware POV? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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