haoxin <xhao@xxxxxxxxxxxxxxxxx> writes: > ( 2023/4/10 H3:52, Huang Ying S: >> 0Day/LKP reported a performance regression for commit >> 7e12beb8ca2a ("migrate_pages: batch flushing TLB"). In the commit, the >> TLB flushing during page migration is batched. So, in >> try_to_migrate_one(), ptep_clear_flush() is replaced with >> set_tlb_ubc_flush_pending(). In further investigation, it is found >> that the TLB flushing can be avoided in ptep_clear_flush() if the PTE >> is inaccessible. In fact, we can optimize in similar way for the >> batched TLB flushing too to improve the performance. >> >> So in this patch, we check pte_accessible() before >> set_tlb_ubc_flush_pending() in try_to_unmap/migrate_one(). Tests show >> that the benchmark score of the anon-cow-rand-mt test case of >> vm-scalability test suite can improve up to 2.1% with the patch on a >> Intel server machine. The TLB flushing IPI can reduce up to 44.3%. >> >> Link: https://lore.kernel.org/oe-lkp/202303192325.ecbaf968-yujie.liu@xxxxxxxxx >> Link: https://lore.kernel.org/oe-lkp/ab92aaddf1b52ede15e2c608696c36765a2602c1.camel@xxxxxxxxx/ >> Fixes: 7e12beb8ca2a ("migrate_pages: batch flushing TLB") >> Reported-by: kernel test robot <yujie.liu@xxxxxxxxx> >> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> >> Cc: Nadav Amit <namit@xxxxxxxxxx> >> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> >> Cc: Hugh Dickins <hughd@xxxxxxxxxx> >> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> >> Cc: David Hildenbrand <david@xxxxxxxxxx> >> --- >> mm/rmap.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/mm/rmap.c b/mm/rmap.c >> index 8632e02661ac..3c7c43642d7c 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1582,7 +1582,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> */ >> pteval = ptep_get_and_clear(mm, address, pvmw.pte); >> - set_tlb_ubc_flush_pending(mm, >> pte_dirty(pteval)); >> + if (pte_accessible(mm, pteval)) >> + set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); >> } else { >> pteval = ptep_clear_flush(vma, address, pvmw.pte); >> } >> @@ -1963,7 +1964,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, >> */ >> pteval = ptep_get_and_clear(mm, address, pvmw.pte); >> - set_tlb_ubc_flush_pending(mm, >> pte_dirty(pteval)); >> + if (pte_accessible(mm, pteval)) >> + set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); > > Just a advice, can you put pte_accessible() into > set_tlb_ubc_flush_pendin(), just like ptep_clear_flush(); so that we > no need to add if (pte_accessible()) in per place > > where call set_tlb_ubc_flush_pending(); Sounds reasonable for me, will do that in the next version. Thanks for suggestion. Best Regards, Huang, Ying >> } else { >> pteval = ptep_clear_flush(vma, address, pvmw.pte); >> }