Re: [PATCH v2 00/12] mm: page migration enhancement for thp

Hi Anshuman,

On Wed, Nov 09, 2016 at 04:03:04PM +0530, Anshuman Khandual wrote:

On 11/08/2016 05:01 AM, Naoya Horiguchi wrote:

quoted

Hi everyone,

I've updated thp migration patches for v4.9-rc2-mmotm-2016-10-27-18-27
with feedbacks for ver.1.

General description (no change since ver.1)
===========================================

This patchset enhances page migration functionality to handle thp migration
for various page migration's callers:
 - mbind(2)
 - move_pages(2)
 - migrate_pages(2)
 - cgroup/cpuset migration
 - memory hotremove
 - soft offline

The main benefit is that we can avoid unnecessary thp splits, which helps us
avoid performance decrease when your applications handles NUMA optimization on
their own.

The implementation is similar to that of normal page migration, the key point
is that we modify a pmd to a pmd migration entry in swap-entry like format.

Will it be better to have new THP_MIGRATE_SUCCESS and THP_MIGRATE_FAIL
VM events to capture how many times the migration worked without first
splitting the huge page and how many time it did not work ?

Thank you for the suggestion.
I think that's helpful, so will try it in next version.

Also do you
have a test case which demonstrates this THP migration and kind of shows
its better than the present split and move method ?

I don't have test cases which compare thp migration and split-then-migration
with some numbers. Maybe measuring/comparing the overhead of migration is
a good start point, although I think the real benefit of thp migration comes
from workload "after migration" by avoiding thp split.

Thanks,
Naoya Horiguchi
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