From: Baolin Wang baolin.wang@linux.alibaba.com
mainline inclusion from mainline-v6.8-rc1 commit 3027c6f8eb9d3857aef08f401aeb7de715410525 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9H84X CVE: NA
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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/431d9fb6823036369dcb1d3b2f63732f01df21a7.169848826... 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 (cherry picked from commit 3027c6f8eb9d3857aef08f401aeb7de715410525) Signed-off-by: Kefeng Wang wangkefeng.wang@huawei.com --- mm/huge_memory.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index cd1eb575f15d..4ce2ed00eaa2 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2556,7 +2556,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, 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);
@@ -2569,6 +2569,8 @@ static void unmap_folio(struct folio *folio) 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)