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Date: Thu, 28 Feb 2008 00:43:17 +0100 From: Andrea Arcangeli <andrea@...ranet.com> To: Christoph Lameter <clameter@....com> Cc: Nick Piggin <npiggin@...e.de>, Steve Wise <swise@...ngridcomputing.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org, Kanoj Sarcar <kanojsarcar@...oo.com>, Roland Dreier <rdreier@...co.com>, Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>, kvm-devel@...ts.sourceforge.net, daniel.blueman@...drics.com, Robin Holt <holt@....com>, general@...ts.openfabrics.org, akpm@...ux-foundation.org Subject: Re: [kvm-devel] [PATCH] mmu notifiers #v7 On Wed, Feb 27, 2008 at 03:06:10PM -0800, Christoph Lameter wrote: > Ok so it somehow works slowly with GRU and you are happy with it. What As far as GRU is concerned, performance is the same as with your patch (Jack can confirm). > about the RDMA folks etc etc? If RDMA/IB folks needed to block in invalidate_range, I guess they need to do so on top of tmpfs too, and that never worked with your patch anyway. > Would it not be better to have a solution that fits all instead of hacking > something in now and then having to modify it later? The whole point is that your solution fits only GRU and KVM too. XPMEM in your patch works in a hacked mode limited to anonymous memory only, Robin already received incoming mail asking to allow xpmem to work on more than anonymous memory, so your solution-that-fits-all doesn't actually fit some of Robin's customer needs. So if it doesn't even entirely satisfy xpmem users, imagine the other potential blocking-users of this code. > Hmmm.. There were earlier discussions of changing the anon vma lock to a > rw lock because of contention issues in large systems. Maybe we can just > generally switch the locks taken while walking rmaps to semaphores? That > would still require to put the invalidate outside of the pte lock. anon_vma lock can remain a spinlock unless you also want to schedule inside try_to_unmap. If converting the i_mmap_lock to a mutex is a big trouble, another way that might work to allow invalidate_range to block, would be to try to boost the mm_users to prevent the mmu_notifier_release to run in another cpu the moment after i_mmap_lock spinlock is unlocked. But even if that works, it'll run slower and the mmu notifiers RCU locking should be switched to a mutex, so it'd be nice to have it as a separate option. -- 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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