Date: Thu, 31 Jan 2008 17:48:19 -0800 (PST)
From: Christoph Lameter <clameter@sgi.com>
To: Andrea Arcangeli <andrea@qumranet.com>
cc: Robin Holt <holt@sgi.com>, Avi Kivity <avi@qumranet.com>,
       Izik Eidus <izike@qumranet.com>, kvm-devel@lists.sourceforge.net,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, steiner@sgi.com,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       daniel.blueman@quadrics.com
Subject: Re: mmu_notifier: close hole in fork
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On Fri, 1 Feb 2008, Andrea Arcangeli wrote:

> Good catch! This was missing also in my #v5 (KVM doesn't need that
> because the only possible cows on sptes can be generated by ksm, but
> it would have been a problem for GRU). The more I think about it, the

How do you think the GRU should know when to drop the refcount? There is 
no page table and thus no way of tracking that a refcount was taken. 
Without the refcount you cannot defer the freeing of the page. So 
shootdown on invalidate_range_begin and lock out until 
invalidate_range_end seems to be the only workable solution.

BTW what do you think about adding a flag parameter to the invalidate 
calls that allows shooting down writable ptes only? That could be useful 
for COW and page_mkclean.

So

#define MMU_ATOMIC 1
#define MMU_WRITABLE 2

insted of the atomic parameter?


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