Re: [PATCH v2 1/2] mm/migrate_device.c: Copy pte dirty bit to page

[Peter Xu <peterx@redhat.com>]

On Tue, Aug 16, 2022 at 04:10:29PM +0800, huang ying wrote:
> > @@ -193,11 +194,10 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> >                         bool anon_exclusive;
> >                         pte_t swp_pte;
> >
> > +                       flush_cache_page(vma, addr, pte_pfn(*ptep));
> > +                       pte = ptep_clear_flush(vma, addr, ptep);
> 
> Although I think it's possible to batch the TLB flushing just before
> unlocking PTL.  The current code looks correct.

If we're with unconditionally ptep_clear_flush(), does it mean we should
probably drop the "unmapped" and the last flush_tlb_range() already since
they'll be redundant?

If that'll need to be dropped, it looks indeed better to still keep the
batch to me but just move it earlier (before unlock iiuc then it'll be
safe), then we can keep using ptep_get_and_clear() afaiu but keep "pte"
updated.

Thanks,

-- 
Peter Xu