Re: [linus:master] [x86] 4817f70c25: stress-ng.mmapaddr.ops_per_sec 63.0% regression

[David Hildenbrand]

On 28.01.25 10:57, kernel test robot wrote:
> hi, Qi Zheng,
>
> this is more a FYI report than a regression report.
>
> by 4817f70c25, parent/4817f70c25 configs have below diff,
>
> --- /pkg/linux/x86_64-rhel-9.4/gcc-12/718b13861d2256ac95d65b892953282a63faf240/.config  2025-01-27 16:20:43.419181382 +0800
> +++ /pkg/linux/x86_64-rhel-9.4/gcc-12/4817f70c25b63ee5e6fd42d376700c058ae16a96/.config  2025-01-26 09:27:16.848625105 +0800
> @@ -1236,6 +1236,8 @@ CONFIG_IOMMU_MM_DATA=y
>   CONFIG_EXECMEM=y
>   CONFIG_NUMA_MEMBLKS=y
>   CONFIG_NUMA_EMU=y
> +CONFIG_ARCH_SUPPORTS_PT_RECLAIM=y
> +CONFIG_PT_RECLAIM=y
>
>   #
>   # Data Access Monitoring
>
>
> this report seems show the impact of PT_CLAIM feature for this stress-ng case.
>
> To us, this is not a code logic regression, but is kind of 'regression' from a
> new feature. anyway, below full report just FYI.

mmapaddr test case seems to mostly do mmap+munmap. No obvious sign of 
MADV_DONTNEED, unless buried somewhere :)

So either

(1) The series is reclaiming page tables outside of MADV_DONTNEED, which
    it shouldn't -- in particular not during munmap() where that happens
    already using the "ordinary" page table removal code for removed
    VMAs.

(2) This is the effect of MMU_GATHER_RCU_TABLE_FREE that gets selected?


I recall a recent series to select MMU_GATHER_RCU_TABLE_FREE on x86 
unconditionally (@Peter, @Rik).

--
Cheers,

David / dhildenb