Messages in this thread | | | Date | Mon, 09 Dec 2013 11:13:50 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH 12/18] mm: numa: Defer TLB flush for THP migration as long as possible |
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On 12/09/2013 02:09 AM, Mel Gorman wrote:
> diff --git a/mm/migrate.c b/mm/migrate.c > index cfb4190..5372521 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1759,6 +1759,12 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm, > goto out_fail; > } > > + /* PTL provides a memory barrier with change_protection_range */ > + ptl = pmd_lock(mm, pmd); > + if (tlb_flush_pending(mm)) > + flush_tlb_range(vma, mmun_start, mmun_end); > + spin_unlock(ptl); > + > /* Prepare a page as a migration target */ > __set_page_locked(new_page); > SetPageSwapBacked(new_page);
I don't think there is a need for that extra memory barrier.
On the "set_tlb_flush_pending, turn ptes into NUMA ones" side, we have a barrier in the form of the page table lock.
We only end up in this code path if the pte/pmd already is a NUMA one, and we take several spinlocks along the way to doing this test. That provides for the memory barrier in this code path.
-- All rights reversed
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