The quilt patch titled Subject: mm: huge_memory: batch tlb flush when splitting a pte-mapped THP has been removed from the -mm tree. Its filename was mm-huge_memory-batch-tlb-flush-when-splitting-a-pte-mapped-thp.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> Subject: mm: huge_memory: batch tlb flush when splitting a pte-mapped THP Date: Mon, 30 Oct 2023 09:11:47 +0800 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@xxxxxxxxxxxxxxxxx Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Reviewed-by: Yang Shi <shy828301@xxxxxxxxx> Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/mm/huge_memory.c~mm-huge_memory-batch-tlb-flush-when-splitting-a-pte-mapped-thp +++ a/mm/huge_memory.c @@ -2379,7 +2379,7 @@ void vma_adjust_trans_huge(struct vm_are static void unmap_folio(struct folio *folio) { enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD | - TTU_SYNC; + TTU_SYNC | TTU_BATCH_FLUSH; VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); @@ -2392,6 +2392,8 @@ static void unmap_folio(struct folio *fo try_to_migrate(folio, ttu_flags); else try_to_unmap(folio, ttu_flags | TTU_IGNORE_MLOCK); + + try_to_unmap_flush(); } static void remap_page(struct folio *folio, unsigned long nr) _ Patches currently in -mm which might be from baolin.wang@xxxxxxxxxxxxxxxxx are