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SubjectRe: [PATCH v2 0/4] Extend migrate_misplaced_page() to support batch migration
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On 8/24/2023 12:51 PM, Huang, Ying wrote:
> Baolin Wang <baolin.wang@linux.alibaba.com> writes:
>
>> On 8/22/2023 10:47 AM, Huang, Ying wrote:
>>> Baolin Wang <baolin.wang@linux.alibaba.com> 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.
>>>>
>>>> In addition, these cleanup can also benefit the compound page's NUMA balancing,
>>>> which was discussed in previous thread[3]. 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 don't find the return number is used except as bool now.
>>
>> As I said above, this is a preparation for batch migration and
>> compound page NUMA balancing in future.
>>
>> In addition, after looking into the THP' NUMA migration, I found this
>> change is necessary for THP migration. Since it is possible that
>> partial subpages were successfully migrated if the THP is split, so
>> below THP numa fault statistics is not always correct:
>>
>> if (page_nid != NUMA_NO_NODE)
>> task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR,
>> flags);
>>
>> I will try to fix this in next version.
>
> IIUC, THP will not be split for NUMA balancing. Please check the
> nosplit logic in migrate_pages_batch().
>
> bool nosplit = (reason == MR_NUMA_MISPLACED);

Yes, I overlooked this. Thanks for reminding.

>
>>> Per my understanding, I still don't find much value of the changes
>>> except as preparation for batch migration in NUMA balancing. So I still
>>
>> IMO, only patch 3 is just a preparation for batch migration, but other
>> patches are some cleanups for migrate_misplaced_page(). I can drop the
>> preparation patches in this series and revise the commit message.
>>
>>> think it's better to wait for the whole series. Where we can check why
>>> these changes are necessary for batch migration. And I think that you
>>> will provide some number to justify the batch migration, including pros
>>> and cons.
>>> --
>>> Best Regards,
>>> Huang, Ying
>>>
>>>> This series is based on the latest mm-unstable(d226b59b30cc).
>>>>
>>>> [1] https://lore.kernel.org/lkml/cover.1639306956.git.baolin.wang@linux.alibaba.com/t/#mc45929849b5d0e29b5fdd9d50425f8e95b8f2563
>>>> [2] https://lore.kernel.org/all/20230213123444.155149-1-ying.huang@intel.com/T/#u
>>>> [3] https://lore.kernel.org/all/f8d47176-03a8-99bf-a813-b5942830fd73@arm.com/
>>>>
>>>> Changes from v1:
>>>> - Move page validation into a new function suggested by Huang Ying.
>>>> - Change numamigrate_isolate_page() to boolean type.
>>>> - Update some commit message.
>>>>
>>>> Baolin Wang (4):
>>>> mm: migrate: factor out migration validation into
>>>> numa_page_can_migrate()
>>>> 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 | 23 +++++++++++++--
>>>> mm/internal.h | 1 +
>>>> mm/memory.c | 43 ++++++++++++++++++++++++++-
>>>> mm/migrate.c | 64 +++++++++--------------------------------
>>>> 5 files changed, 88 insertions(+), 58 deletions(-)

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