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3027c6f8eb
I can observe an obvious tlb flush hotspot when splitting a pte-mapped THP
on 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.
Actually, there is no need to flush tlb for each subpage immediately,
instead we can batch tlb flush for the pte-mapped THP to improve the
performance.
After this patch, we can see the batch tlb flush can improve the latency
obviously when running thpscale.
k6.5-base patched
Amean fault-both-1 1071.17 ( 0.00%) 901.83 * 15.81%*
Amean fault-both-3 2386.08 ( 0.00%) 1865.32 * 21.82%*
Amean fault-both-5 2851.10 ( 0.00%) 2273.84 * 20.25%*
Amean fault-both-7 3679.91 ( 0.00%) 2881.66 * 21.69%*
Amean fault-both-12 5916.66 ( 0.00%) 4369.55 * 26.15%*
Amean fault-both-18 7981.36 ( 0.00%) 6303.57 * 21.02%*
Amean fault-both-24 10950.79 ( 0.00%) 8752.56 * 20.07%*
Amean fault-both-30 14077.35 ( 0.00%) 10170.01 * 27.76%*
Amean fault-both-32 13061.57 ( 0.00%) 11630.08 * 10.96%*
Link: https://lkml.kernel.org/r/431d9fb6823036369dcb1d3b2f63732f01df21a7.1698488264.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
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