Re: [PATCH 0/4] Extend migrate_misplaced_page() to support batch migration

[Huang, Ying]

Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:

> On 8/21/2023 10:29 AM, Huang, Ying wrote:
>> Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
>> 
>>> Hi,
>>>
>>> Currently, on our ARM servers with NUMA enabled, we found the cross-die latency
>>> is a little larger that will significantly impact the workload's performance.
>>> So on ARM servers we will rely on the NUMA balancing to avoid the cross-die
>>> accessing. And I posted a patchset[1] to support speculative numa fault to
>>> improve the NUMA balancing's performance according to the principle of data
>>> locality. Moreover, thanks to Huang Ying's patchset[2], which introduced batch
>>> migration as a way to reduce the cost of TLB flush, and it will also benefit
>>> the migration of multiple pages all at once during NUMA balancing.
>>>
>>> So we plan to continue to support batch migration in do_numa_page() to improve
>>> the NUMA balancing's performance, but before adding complicated batch migration
>>> algorithm for NUMA balancing, some cleanup and preparation work need to do firstly,
>>> which are done in this patch set. In short, this patchset extends the
>>> migrate_misplaced_page() interface to support batch migration, and no functional
>>> changes intended.
>> Will these cleanup benefit anything except batching migration?  If
>> not,
>
> I hope these cleanup can also benefit the compound page's NUMA
> balancing, which was discussed in the thread[1]. IIUC, for the
> compound page's NUMA balancing, it is possible that partial pages were
> successfully migrated, so it is necessary to return the number of
> pages that were successfully migrated from
> migrate_misplaced_page(). (But I did not look this in detail yet,
> please correct me if I missed something, and I will find some time to
> look this in detail). That is why I think these cleanups are
> straightforward.
>
> Yes, I will post the batch migration patches after more polish and
> testing, but I think these cleanups are separate and straightforward,
> so I plan to submit the patches separately.

Then, please state the benefit explicitly in the patch description
instead of just preparation for batching migration.

--
Best Regards,
Huang, Ying

> [1]
> https://lore.kernel.org/all/f8d47176-03a8-99bf-a813-b5942830fd73@xxxxxxx/
>
>> I suggest you to post the whole series.  In this way, people will be
>> more clear about why we need these cleanup.
>> --
>> Best Regards,
>> Huang, Ying
>> 
>>> [1] https://lore.kernel.org/lkml/cover.1639306956.git.baolin.wang@xxxxxxxxxxxxxxxxx/t/#mc45929849b5d0e29b5fdd9d50425f8e95b8f2563
>>> [2] https://lore.kernel.org/all/20230213123444.155149-1-ying.huang@xxxxxxxxx/T/#u
>>>
>>> Baolin Wang (4):
>>>    mm: migrate: move migration validation into numa_migrate_prep()
>>>    mm: migrate: move the numamigrate_isolate_page() into do_numa_page()
>>>    mm: migrate: change migrate_misplaced_page() to support multiple pages
>>>      migration
>>>    mm: migrate: change to return the number of pages migrated
>>>      successfully
>>>
>>>   include/linux/migrate.h | 15 ++++++++---
>>>   mm/huge_memory.c        | 19 +++++++++++---
>>>   mm/memory.c             | 34 +++++++++++++++++++++++-
>>>   mm/migrate.c            | 58 ++++++++---------------------------------
>>>   4 files changed, 71 insertions(+), 55 deletions(-)