Cc: Christoph Lameter <clameter@...>, <akpm@...>, Nick Piggin <npiggin@...>, Steve Wise <swise@...>, Peter Zijlstra <a.p.zijlstra@...>, <linux-mm@...>, Kanoj Sarcar <kanojsarcar@...>, Roland Dreier <rdreier@...>, Jack Steiner <steiner@...>, <linux-kernel@...>, Avi Kivity <avi@...>, <kvm-devel@...>, <general@...>, Hugh Dickins <hugh@...>
On Tue, Apr 22, 2008 at 08:36:04AM -0500, Robin Holt wrote:
There's no value for anything but get_user_pages (get_user_pages takes
its own lock internally though). I preferred to explain it as a
seqlock because it was simpler for reading, but I totally agree in the
final implementation it shouldn't be a seqlock. My code was meant to
be pseudo-code only. It doesn't even need to be atomic ;).
1) when armed the time-window where the kvm-page-fault would be
blocked would be a bit larger without invalidate_page for no good
reason
2) if you were to remove invalidate_page when disarmed the VM could
would need two branches instead of one in various places
I don't want to waste cycles if not wasting them improves performance
both when armed and disarmed.
I actually meant for both.
For rmap is sure effective free, for do_wp_page it costs one branch
for no good reason.
Agreed.
Sure, we have that patch now, I'll send it out in a minute, I was just
trying to explain why it makes sense to have an invalidate_page too
(which remains the only difference by now), removing it would be a
regression on all sides, even if a minor one.
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