Messages in this thread | | | Date | Thu, 2 Nov 2023 15:10:49 +0800 | Subject | Re: [PATCH] mm: huge_memory: batch tlb flush when splitting a pte-mapped THP | From | Baolin Wang <> |
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On 11/1/2023 2:13 PM, Alistair Popple wrote: > > Baolin Wang <baolin.wang@linux.alibaba.com> writes: > >> I can observe an obvious tlb flush hotpot when splitting a pte-mapped THP on > > A tlb flush hotpot does sound delicious, but I think you meant hotspot :-)
Ah, yes. Hope Andrew can help to fix it :)
>> my ARM64 server, and the distribution of this hotspot is as follows: >> >> - 16.85% split_huge_page_to_list >> + 7.80% down_write >> - 7.49% try_to_migrate >> - 7.48% rmap_walk_anon >> 7.23% ptep_clear_flush >> + 1.52% __split_huge_page >> >> The reason is that the split_huge_page_to_list() will build migration entries >> for each subpage of a pte-mapped Anon THP by try_to_migrate(), or unmap for >> file THP, and it will clear and tlb flush for each subpage's pte. Moreover, >> the split_huge_page_to_list() will set TTU_SPLIT_HUGE_PMD flag to ensure >> the THP is already a pte-mapped THP before splitting it to some normal pages. > > The only other user of TTU_SPLIT_HUGE_PMD is vmscan which also sets > TTU_BATCH_FLUSH so we could make the former imply the latter but that > seem dangerous given the requirement to call try_to_unmap_flush() so > best not to. > > Reviewed-by: Alistair Popple <apopple@nvidia.com>
Thanks for reviewing, and also thanks to Ying and Yang.
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