Re: [linus:master] [mm] 0ba09b1733: will-it-scale.per_thread_ops -21.1% regression in mmap1 benchmark

["Yin, Fengwei" <fengwei.yin@intel.com>]

On 12/22/2022 12:45 AM, Yang Shi wrote:
>> We caught two mmap1 regressions on mailine, please see the data below:
>>
>> 830b3c68c1fb1 Linux 6.1                                                              2085 2355 2088
>> 76dcd734eca23 Linux 6.1-rc8                                                          2093 2082 2094 2073 2304 2088
>> 0ba09b1733878 Revert "mm: align larger anonymous mappings on THP boundaries"         2124 2286 2086 2114 2065 2081
>> 23393c6461422 char: tpm: Protect tpm_pm_suspend with locks                           2756 2711 2689 2696 2660 2665
>> b7b275e60bcd5 Linux 6.1-rc7                                                          2670 2656 2720 2691 2667
>> ...
>> 9abf2313adc1c Linux 6.1-rc1                                                          2725 2717 2690 2691 2710
>> 3b0e81a1cdc9a mmap: change zeroing of maple tree in __vma_adjust()                   2736 2781 2748
>> 524e00b36e8c5 mm: remove rb tree.                                                    2747 2744 2747
>> 0c563f1480435 proc: remove VMA rbtree use from nommu
>> d0cf3dd47f0d5 damon: convert __damon_va_three_regions to use the VMA iterator
>> 3499a13168da6 mm/mmap: use maple tree for unmapped_area{_topdown}
>> 7fdbd37da5c6f mm/mmap: use the maple tree for find_vma_prev() instead of the rbtree
>> f39af05949a42 mm: add VMA iterator
>> d4af56c5c7c67 mm: start tracking VMAs with maple tree
>> e15e06a839232 lib/test_maple_tree: add testing for maple tree                        4638 4628 4502
>> 9832fb87834e2 mm/demotion: expose memory tier details via sysfs                      4625 4509 4548
>> 4fe89d07dcc28 Linux 6.0                                                              4385 4205 4348 4228 4504
>>
>>
>> The first regression was between v6.0 and v6.1-rc1. The score dropped
>> from 4600 to 2700, and bisected to the patches switching from rb tree to
>> maple tree. This was reported at
>> https://lore.kernel.org/oe-lkp/202212191714.524e00b3-yujie.liu@intel.com/
>> Thanks for the explanation that it is an expected regression as a trade
>> off to benefit read performance.
>>
>> The second regression was between v6.1-rc7 and v6.1-rc8. The score
>> dropped from 2700 to 2100, and bisected to this "Revert "mm: align larger
>> anonymous mappings on THP boundaries"" commit.
> So it means "mm: align larger anonymous mappings on THP boundaries"
> actually improved the mmap1 benchmark? But it caused regression for
> other usecase, for example, building kernel with clang, which is a
> regression for a real life usecase.
Yes. The patch "mm: align larger anonymous mappings on THP boundaries"
can improve the mmap1 benchmark.

For building kernel regression, looks like it's not related with the
patch "mm: align larger anonymous mappings on THP boundaries" directly.
It's another existing behavior more visible with the patch.
https://lore.kernel.org/all/a4bcddad-e56f-cedc-891a-916e86d9a02c@intel.com/


Regards
Yin, Fengwei

>