On 21.05.24 06:02, Lance Yang wrote:
In preparation for supporting try_to_unmap_one() to unmap PMD-mapped
folios, start the pagewalk first, then call split_huge_pmd_address() to
split the folio.
Since TTU_SPLIT_HUGE_PMD will no longer perform immediately, we might
encounter a PMD-mapped THP missing the mlock in the VM_LOCKED range during
the page walk. It’s probably necessary to mlock this THP to prevent it from
being picked up during page reclaim.
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Suggested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
---
[...] again, sorry for the late review.
diff --git a/mm/rmap.c b/mm/rmap.c
index ddffa30c79fb..08a93347f283 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1640,9 +1640,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
if (flags & TTU_SYNC)
pvmw.flags = PVMW_SYNC;
- if (flags & TTU_SPLIT_HUGE_PMD)
- split_huge_pmd_address(vma, address, false, folio);
-
/*
* For THP, we have to assume the worse case ie pmd for invalidation.
* For hugetlb, it could be much worse if we need to do pud
@@ -1668,20 +1665,35 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
mmu_notifier_invalidate_range_start(&range);
while (page_vma_mapped_walk(&pvmw)) {
- /* Unexpected PMD-mapped THP? */
- VM_BUG_ON_FOLIO(!pvmw.pte, folio);
-
/*
* If the folio is in an mlock()d vma, we must not swap it out.
*/
if (!(flags & TTU_IGNORE_MLOCK) &&
(vma->vm_flags & VM_LOCKED)) {
/* Restore the mlock which got missed */
- if (!folio_test_large(folio))
+ if (!folio_test_large(folio) ||
+ (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD)))
mlock_vma_folio(folio, vma);
Can you elaborate why you think this would be required? If we would have
performed the split_huge_pmd_address() beforehand, we would still be
left with a large folio, no?
goto walk_done_err;
}
+ if (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD)) {
+ /*
+ * We temporarily have to drop the PTL and start once
+ * again from that now-PTE-mapped page table.
+ */
+ split_huge_pmd_locked(vma, range.start, pvmw.pmd, false,
+ folio);
Using range.start here is a bit weird. Wouldn't this be pvmw.address?
[did not check]
+ pvmw.pmd = NULL;
+ spin_unlock(pvmw.ptl);
+ pvmw.ptl = NULL;
Would we want a
page_vma_mapped_walk_restart() that is exactly for that purpose?
+ flags &= ~TTU_SPLIT_HUGE_PMD;
+ continue;
+ }
+
+ /* Unexpected PMD-mapped THP? */
+ VM_BUG_ON_FOLIO(!pvmw.pte, folio);
--
Cheers,
David / dhildenb
