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)); } else { pteval = ptep_clear_flush(vma, address, pvmw.pte); } -- 2.39.2