Messages in this thread | | | Date | Wed, 7 Nov 2012 10:38:39 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH 08/19] mm: numa: Create basic numa page hinting infrastructure |
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On Tue, Nov 06, 2012 at 01:58:26PM -0500, Rik van Riel wrote: > On 11/06/2012 04:14 AM, Mel Gorman wrote: > >Note: This patch started as "mm/mpol: Create special PROT_NONE > > infrastructure" and preserves the basic idea but steals *very* > > heavily from "autonuma: numa hinting page faults entry points" for > > the actual fault handlers without the migration parts. The end > > result is barely recognisable as either patch so all Signed-off > > and Reviewed-bys are dropped. If Peter, Ingo and Andrea are ok with > > this version, I will re-add the signed-offs-by to reflect the history. > > > >In order to facilitate a lazy -- fault driven -- migration of pages, create > >a special transient PAGE_NUMA variant, we can then use the 'spurious' > >protection faults to drive our migrations from. > > > >Pages that already had an effective PROT_NONE mapping will not be detected > > The patch itself is good, but the changelog needs a little > fix. While you are defining _PAGE_NUMA to _PAGE_PROTNONE on > x86, this may be different on other architectures. > > Therefore, the changelog should refer to PAGE_NUMA, not > PROT_NONE. >
Fair point. I still want to record the point that PROT_NONE will not generate the faults though. How about this?
In order to facilitate a lazy -- fault driven -- migration of pages, create a special transient PAGE_NUMA variant, we can then use the 'spurious' protection faults to drive our migrations from.
The meaning of PAGE_NUMA depends on the architecture but on x86 it is effectively PROT_NONE. In this case, PROT_NONE mappings will not be detected to generate these 'spurious' faults for the simple reason that we cannot distinguish them on their protection bits, see pte_numa(). This isn't a problem since PROT_NONE (and possible PROT_WRITE with dirty tracking) aren't used or are rare enough for us to not care about their placement.
> >to generate these 'spurious' faults for the simple reason that we cannot > >distinguish them on their protection bits, see pte_numa(). This isn't > >a problem since PROT_NONE (and possible PROT_WRITE with dirty tracking) > >aren't used or are rare enough for us to not care about their placement. > > > >Signed-off-by: Mel Gorman <mgorman@suse.de> > > Other than the changelog ... > > Reviewed-by: Rik van Riel <riel@redhat.com>
Thanks.
-- Mel Gorman SUSE Labs
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