Re: [RFC PATCH 0/7] add mTHP support for wp

[zhangqilong <zhangqilong3@huawei.com>]

> 
> Hi all,
> 
> This patchset is introduced to make pagefault write-protect copy support
> mthp, with this series, pagefault write-protect copy will have a 9-14%
> performance improvement.
> 
> Currently pagefaults on anonymous pages support mthp [1], and hardware
> features (such as arm64 contpte) can be used to store multiple ptes in one
> TLB entry, reducing the probability of TLB misses. However, when the
> process is forked and the cow is triggered again, the above optimization
> effect is lost, and only 4KB is requested once at a time.
> 
> Therefore, make pagefault write-protect copy support mthp to maintain the
> optimization effect of TLB and improve the efficiency of cow pagefault.
> 
> vm-scalability usemem shows a great improvement, test using: usemem -n
> 32 --prealloc --prefault 249062617 (result unit is KB/s, bigger is better)
> 
> |    size     | w/o patch | w/ patch  |  delta  |
> |-------------|-----------|-----------|---------|
> | baseline 4K | 723041.63 | 717643.21 | -0.75%  |
> | mthp 16K    | 732871.14 | 799513.18 | +9.09%  |
> | mthp 32K    | 746060.91 | 836261.83 | +12.09% |
> | mthp 64K    | 747333.18 | 855570.43 | +14.48% |
> 
> This series is based on Linux v6.16 (038d61fd6422).
> 
> Thanks,
> Vernon
> 
> [1] https://lore.kernel.org/all/20231207161211.2374093-1-
> ryan.roberts@arm.com/
> 
> Vernon Yang (7):
>   mm: memory: replace single-operation with multi-operation in wp
>   mm: memory: add ptep_clear_flush_range function
>   mm: memory: add kmsan_copy_pages_meta function
>   mm: memory: add offset to start copy for copy_user_gigantic_page
>   mm: memory: improve wp_page_copy readability
>   mm: memory: add mTHP support for wp

Oh, we are also doing similar optimizations, but only for the code segment. :)

>   selftests: mm: support wp mTHP collapse testing
> 
>  include/linux/huge_mm.h                 |   3 +
>  include/linux/kmsan.h                   |  13 +-
>  include/linux/mm.h                      |   8 +
>  include/linux/pgtable.h                 |   3 +
>  mm/hugetlb.c                            |   6 +-
>  mm/kmsan/shadow.c                       |  26 +-
>  mm/memory.c                             | 309 ++++++++++++++++++------
>  mm/pgtable-generic.c                    |  20 ++
>  tools/testing/selftests/mm/khugepaged.c |   5 +-
>  9 files changed, 302 insertions(+), 91 deletions(-)
> 
> --
> 2.50.1
>