Re: question on NUMA page migration

From: Rik van Riel
Date: Sat Oct 20 2012 - 12:02:39 EST

On 10/19/2012 09:23 PM, Ingo Molnar wrote:

* Rik van Riel <riel@xxxxxxxxxx> wrote:

On 10/19/2012 01:53 PM, Peter Zijlstra wrote:
On Fri, 2012-10-19 at 13:13 -0400, Rik van Riel wrote:

Another alternative might be to do the put_page inside
do_prot_none_numa(). That would be analogous to do_wp_page
disposing of the old page for the caller.

It'd have to be inside migrate_misplaced_page(), can't do before
isolate_lru_page() or the page might disappear. Doing it after is
(obviously) too late.

Keeping an extra refcount on the page might _still_
result in it disappearing from the process by some
other means, in-between you grabbing the refcount
and invoking migration of the page.

I am not real happy about NUMA migration introducing its own
migration mode...

You didn't seem to mind too much earlier, but I can remove it if you

Could have been reviewing fatigue :)


And yes, it would have been nice to not have a special
migration mode for sched/numa.

Speaking of, when do you guys plan to submit a (cleaned up)
version of the sched/numa patch series for review on lkml?

Which commit(s) worry you specifically?

One of them would be the commit that introduces MIGRATE_FAULT.
Adding it in one patch, and removing it into a next just makes
things harder on the reviewers.


If the changesets with NUMA syscalls are still in your tree's
history, they should not be submitted as part of the patch
series, either.
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