On 20 Jul 2021, at 16:53, Yang Shi wrote: > On Tue, Jul 20, 2021 at 7:25 AM Christian Borntraeger > wrote: >> >> >> >> On 20.07.21 08:55, Huang Ying wrote: >>> Before the commit c5b5a3dd2c1f ("mm: thp: refactor NUMA fault >>> handling"), the TLB flushing is done in do_huge_pmd_numa_page() itself >>> via flush_tlb_range(). >>> >>> But after commit c5b5a3dd2c1f ("mm: thp: refactor NUMA fault >>> handling"), the TLB flushing is done in migrate_pages() as in the >>> following code path anyway. >>> >>> do_huge_pmd_numa_page >>> migrate_misplaced_page >>> migrate_pages >>> >>> So now, the TLB flushing code in do_huge_pmd_numa_page() becomes >>> unnecessary. So the code is deleted in this patch to simplify the >>> code. This is only code cleanup, there's no visible performance >>> difference. >>> >>> Signed-off-by: "Huang, Ying" >>> Cc: Yang Shi >>> Cc: Dan Carpenter >>> Cc: Mel Gorman >>> Cc: Christian Borntraeger >>> Cc: Gerald Schaefer >>> Cc: Heiko Carstens >>> Cc: Hugh Dickins >>> Cc: Andrea Arcangeli >>> Cc: Kirill A. Shutemov >>> Cc: Michal Hocko >>> Cc: Vasily Gorbik >>> Cc: Zi Yan >>> --- >>> mm/huge_memory.c | 26 -------------------------- >>> 1 file changed, 26 deletions(-) >>> >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index afff3ac87067..9f21e44c9030 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -1440,32 +1440,6 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf) >>> goto out; >>> } >>> >>> - /* >>> - * Since we took the NUMA fault, we must have observed the !accessible >>> - * bit. Make sure all other CPUs agree with that, to avoid them >>> - * modifying the page we're about to migrate. >>> - * >>> - * Must be done under PTL such that we'll observe the relevant >>> - * inc_tlb_flush_pending(). >>> - * >>> - * We are not sure a pending tlb flush here is for a huge page >>> - * mapping or not. Hence use the tlb range variant >>> - */ >>> - if (mm_tlb_flush_pending(vma->vm_mm)) { >>> - flush_tlb_range(vma, haddr, haddr + HPAGE_PMD_SIZE); >>> - /* >>> - * change_huge_pmd() released the pmd lock before >>> - * invalidating the secondary MMUs sharing the primary >>> - * MMU pagetables (with ->invalidate_range()). The >>> - * mmu_notifier_invalidate_range_end() (which >>> - * internally calls ->invalidate_range()) in >>> - * change_pmd_range() will run after us, so we can't >>> - * rely on it here and we need an explicit invalidate. >>> - */ >>> - mmu_notifier_invalidate_range(vma->vm_mm, haddr, >>> - haddr + HPAGE_PMD_SIZE); >>> - } >>> CC Paolo/KVM list so we also remove the mmu notifier here. Do we need those >> now in migrate_pages? I am not an expert in that code, but I cant find >> an equivalent mmu_notifier in migrate_misplaced_pages. >> I might be totally wrong, just something that I noticed. > > Do you mean the missed mmu notifier invalidate for the THP migration > case? Yes, I noticed that too. But I'm not sure whether it is intended > or just missed. From my understand of mmu_notifier document, mmu_notifier_invalidate_range() is needed only if the PTE is updated to point to a new page or the page pointed by the PTE is freed. Page migration does not fall into either case. In addition, in migrate_pages(), more specifically try_to_migrate_one(), there is a pair of mmu_notifier_invalidate_range_start() and mmu_notifier_invalidate_range_end() around the PTE manipulation code, which should be sufficient to notify secondary TLBs (including KVM) about the PTE change for page migration. Correct me if I am wrong. — Best Regards, Yan, Zi