Re: [PATCH] mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing code

[Christian Borntraeger]

On 22.07.21 02:26, Huang, Ying wrote:
> Sean Christopherson <seanjc@xxxxxxxxxx> writes:
> > > Thanks, I think you are correct. By looking into commit 7066f0f933a1
> > > ("mm: thp: fix mmu_notifier in migrate_misplaced_transhuge_page()"),
> > > the tlb flush and mmu notifier invalidate were needed since the old
> > > numa fault implementation didn't change PTE to migration entry so it
> > > may cause data corruption due to the writes from GPU secondary MMU.
> > >
> > > The refactor does use the generic migration code which converts PTE to
> > > migration entry before copying data to the new page.
> >
> > That's my understanding as well, based on this blurb from commit 7066f0f933a1.
> >
> >      The standard PAGE_SIZEd migrate_misplaced_page is less accelerated and
> >      uses the generic migrate_pages which transitions the pte from
> >      numa/protnone to a migration entry in try_to_unmap_one() and flushes TLBs
> >      and all mmu notifiers there before copying the page.
> >
> > That analysis/justification for removing the invalidate_range() call should be
> > captured in the changelog.  Confirmation from Andrea would be a nice bonus.
>
> When we flush CPU TLB for a page that may be shared with device/VM TLB,
> we will call MMU notifiers for the page to flush the device/VM TLB.
> Right?  So when we replaced CPU TLB flushing in do_huge_pmd_numa_page()
> with that in try_to_migrate_one(), we will replace the MMU notifiers
> calling too.  Do you agree?

Can someone write an updated commit messages that contains this information?