Re: [PATCH -v4 0/9] migrate_pages(): batch TLB flushing

[haoxin <xhao@linux.alibaba.com>]

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在 2023/2/8 下午2:21, haoxin 写道:
>
> On my arm64 server with 128 cores, 2 numa nodes.
>
> I used memhog as benchmark :
>
>     numactl -m -C 5 memhog -r100000 1G
>
     Do a fix, numactl -m 0 -C 5 memhog -r100000 1G

> The test result as below:
>
>  With this patch:
>
>     #time migratepages 8490 0 1
>
>     real 0m1.161s
>
>     user 0m0.000s
>
>     sys 0m1.161s
>
> without this patch:
>
>     #time migratepages 8460 0 1
>
>     real 0m2.068s
>
>     user 0m0.001s
>
>     sys 0m2.068s
>
> So you can see the migration performance improvement about *+78%*
>
> This is the perf record info.
>
> w/o
> +   51.07%     0.09%  migratepages  [kernel.kallsyms]  [k] 
> migrate_folio_extra
> +   42.43%     0.04%  migratepages  [kernel.kallsyms]  [k] folio_copy
> +   42.34%    42.34%  migratepages  [kernel.kallsyms]  [k] __pi_copy_page
> +   33.99%     0.09%  migratepages  [kernel.kallsyms]  [k] rmap_walk_anon
> +   32.35%     0.04%  migratepages  [kernel.kallsyms]  [k] try_to_migrate
> *+   27.78%    27.78%  migratepages  [kernel.kallsyms]  [k] 
> ptep_clear_flush *
> +    8.19%     6.64%  migratepages  [kernel.kallsyms]  [k] 
> folio_migrate_flagsmigrati_tlb_flush
>
> w/ this patch
> +   18.57%     0.13%  migratepages     [kernel.kallsyms]   [k] 
> migrate_pages
> +   18.23%     0.07%  migratepages     [kernel.kallsyms]   [k] 
> migrate_pages_batch
> +   16.29%     0.13%  migratepages     [kernel.kallsyms]   [k] 
> migrate_folio_move
> +   12.73%     0.10%  migratepages     [kernel.kallsyms]   [k] 
> move_to_new_folio
> +   12.52%     0.06%  migratepages     [kernel.kallsyms]   [k] 
> migrate_folio_extra
>
> Therefore, this patch helps improve performance in page migration
>
>
> So,  you can add Tested-by: Xin Hao <xhao@linux.alibaba.com>
>
>
> 在 2023/2/6 下午2:33, Huang Ying 写道:
>> From: "Huang, Ying"<ying.huang@intel.com>
>>
>> Now, migrate_pages() migrate folios one by one, like the fake code as
>> follows,
>>
>>    for each folio
>>      unmap
>>      flush TLB
>>      copy
>>      restore map
>>
>> If multiple folios are passed to migrate_pages(), there are
>> opportunities to batch the TLB flushing and copying.  That is, we can
>> change the code to something as follows,
>>
>>    for each folio
>>      unmap
>>    for each folio
>>      flush TLB
>>    for each folio
>>      copy
>>    for each folio
>>      restore map
>>
>> The total number of TLB flushing IPI can be reduced considerably.  And
>> we may use some hardware accelerator such as DSA to accelerate the
>> folio copying.
>>
>> So in this patch, we refactor the migrate_pages() implementation and
>> implement the TLB flushing batching.  Base on this, hardware
>> accelerated folio copying can be implemented.
>>
>> If too many folios are passed to migrate_pages(), in the naive batched
>> implementation, we may unmap too many folios at the same time.  The
>> possibility for a task to wait for the migrated folios to be mapped
>> again increases.  So the latency may be hurt.  To deal with this
>> issue, the max number of folios be unmapped in batch is restricted to
>> no more than HPAGE_PMD_NR in the unit of page.  That is, the influence
>> is at the same level of THP migration.
>>
>> We use the following test to measure the performance impact of the
>> patchset,
>>
>> On a 2-socket Intel server,
>>
>>   - Run pmbench memory accessing benchmark
>>
>>   - Run `migratepages` to migrate pages of pmbench between node 0 and
>>     node 1 back and forth.
>>
>> With the patch, the TLB flushing IPI reduces 99.1% during the test and
>> the number of pages migrated successfully per second increases 291.7%.
>>
>> This patchset is based on v6.2-rc4.
>>
>> Changes:
>>
>> v4:
>>
>> - Fixed another bug about non-LRU folio migration.  Thanks Hyeonggon!
>>
>> v3:
>>
>> - Rebased on v6.2-rc4
>>
>> - Fixed a bug about non-LRU folio migration.  Thanks Mike!
>>
>> - Fixed some comments.  Thanks Baolin!
>>
>> - Collected reviewed-by.
>>
>> v2:
>>
>> - Rebased on v6.2-rc3
>>
>> - Fixed type force cast warning.  Thanks Kees!
>>
>> - Added more comments and cleaned up the code.  Thanks Andrew, Zi, Alistair, Dan!
>>
>> - Collected reviewed-by.
>>
>> from rfc to v1:
>>
>> - Rebased on v6.2-rc1
>>
>> - Fix the deadlock issue caused by locking multiple pages synchronously
>>    per Alistair's comments.  Thanks!
>>
>> - Fix the autonumabench panic per Rao's comments and fix.  Thanks!
>>
>> - Other minor fixes per comments. Thanks!
>>
>> Best Regards,
>> Huang, Ying

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