Messages in this thread | | | From | Yang Shi <> | Date | Tue, 20 Jul 2021 13:53:39 -0700 | Subject | Re: [PATCH] mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing code |
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On Tue, Jul 20, 2021 at 7:25 AM Christian Borntraeger <borntraeger@de.ibm.com> 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" <ying.huang@intel.com> > > Cc: Yang Shi <shy828301@gmail.com> > > Cc: Dan Carpenter <dan.carpenter@oracle.com> > > Cc: Mel Gorman <mgorman@suse.de> > > Cc: Christian Borntraeger <borntraeger@de.ibm.com> > > Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com> > > Cc: Heiko Carstens <hca@linux.ibm.com> > > Cc: Hugh Dickins <hughd@google.com> > > Cc: Andrea Arcangeli <aarcange@redhat.com> > > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > Cc: Michal Hocko <mhocko@suse.com> > > Cc: Vasily Gorbik <gor@linux.ibm.com> > > Cc: Zi Yan <ziy@nvidia.com> > > --- > > 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.
Zi Yan is the author for THP migration code, he may have some clue.
> > > pmd = pmd_modify(oldpmd, vma->vm_page_prot); > > page = vm_normal_page_pmd(vma, haddr, pmd); > > if (!page) > >
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