Re: [PATCH v2 3/3] mm: rmap: Use flush_cache_range() to flush cache for hugetlb pages
From: Baolin Wang
Date: Tue May 03 2022 - 22:49:00 EST
On 5/4/2022 4:17 AM, Mike Kravetz wrote:
On 4/27/22 03:52, Baolin Wang wrote:
Now we will use flush_cache_page() to flush cache for anonymous hugetlb
pages when unmapping or migrating a hugetlb page mapping, but the
flush_cache_page() only handles a PAGE_SIZE range on some architectures
(like arm32, arc and so on), which will cause potential cache issues.
Thus change to use flush_cache_range() to cover the whole size of a
hugetlb page.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 90 ++++++++++++++++++++++++++++++++++-----------------------------
1 file changed, 48 insertions(+), 42 deletions(-)
diff --git a/mm/rmap.c b/mm/rmap.c
index 4f0d115..6fdd198 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1528,13 +1528,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
anon_exclusive = folio_test_anon(folio) &&
PageAnonExclusive(subpage);
- if (folio_test_hugetlb(folio) && !folio_test_anon(folio)) {
- /*
- * To call huge_pmd_unshare, i_mmap_rwsem must be
- * held in write mode. Caller needs to explicitly
- * do this outside rmap routines.
- */
- VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
+ if (folio_test_hugetlb(folio)) {
/*
* huge_pmd_unshare may unmap an entire PMD page.
* There is no way of knowing exactly which PMDs may
@@ -1544,22 +1538,31 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
*/
flush_cache_range(vma, range.start, range.end);
- if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) {
- flush_tlb_range(vma, range.start, range.end);
- mmu_notifier_invalidate_range(mm, range.start,
- range.end);
-
+ if (!folio_test_anon(folio)) {
/*
- * The ref count of the PMD page was dropped
- * which is part of the way map counting
- * is done for shared PMDs. Return 'true'
- * here. When there is no other sharing,
- * huge_pmd_unshare returns false and we will
- * unmap the actual page and drop map count
- * to zero.
+ * To call huge_pmd_unshare, i_mmap_rwsem must be
+ * held in write mode. Caller needs to explicitly
+ * do this outside rmap routines.
*/
- page_vma_mapped_walk_done(&pvmw);
- break;
+ VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
+
+ if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) {
+ flush_tlb_range(vma, range.start, range.end);
+ mmu_notifier_invalidate_range(mm, range.start,
+ range.end);
+
+ /*
+ * The ref count of the PMD page was dropped
+ * which is part of the way map counting
+ * is done for shared PMDs. Return 'true'
+ * here. When there is no other sharing,
+ * huge_pmd_unshare returns false and we will
+ * unmap the actual page and drop map count
+ * to zero.
+ */
+ page_vma_mapped_walk_done(&pvmw);
+ break;
+ }
}
} else {
flush_cache_page(vma, address, pte_pfn(*pvmw.pte));
@@ -1885,13 +1888,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
anon_exclusive = folio_test_anon(folio) &&
PageAnonExclusive(subpage);
- if (folio_test_hugetlb(folio) && !folio_test_anon(folio)) {
- /*
- * To call huge_pmd_unshare, i_mmap_rwsem must be
- * held in write mode. Caller needs to explicitly
- * do this outside rmap routines.
- */
- VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
+ if (folio_test_hugetlb(folio)) {
/*
* huge_pmd_unshare may unmap an entire PMD page.
* There is no way of knowing exactly which PMDs may
@@ -1901,22 +1898,31 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
*/
flush_cache_range(vma, range.start, range.end);
- if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) {
- flush_tlb_range(vma, range.start, range.end);
- mmu_notifier_invalidate_range(mm, range.start,
- range.end);
-
+ if (!folio_test_anon(folio)) {
/*
- * The ref count of the PMD page was dropped
- * which is part of the way map counting
- * is done for shared PMDs. Return 'true'
- * here. When there is no other sharing,
- * huge_pmd_unshare returns false and we will
- * unmap the actual page and drop map count
- * to zero.
+ * To call huge_pmd_unshare, i_mmap_rwsem must be
+ * held in write mode. Caller needs to explicitly
+ * do this outside rmap routines.
*/
- page_vma_mapped_walk_done(&pvmw);
- break;
+ VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
+
+ if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) {
+ flush_tlb_range(vma, range.start, range.end);
+ mmu_notifier_invalidate_range(mm, range.start,
+ range.end);
+
+ /*
+ * The ref count of the PMD page was dropped
+ * which is part of the way map counting
+ * is done for shared PMDs. Return 'true'
+ * here. When there is no other sharing,
+ * huge_pmd_unshare returns false and we will
+ * unmap the actual page and drop map count
+ * to zero.
+ */
+ page_vma_mapped_walk_done(&pvmw);
+ break;
+ }
}
} else {
flush_cache_page(vma, address, pte_pfn(*pvmw.pte));
Thanks,
The code looks fine. It is unfortunate that we need so many levels of
indenting and exceed 80 columns. But, that is OK.
I'll do a cleanup to make it more readable with factoring the hugetlb
case into a new function after the fix series[1].
[1]
https://lore.kernel.org/linux-arm-kernel/20220503120343.6264e126@thinkpad/T/
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
I see you have a followup series to address the call to ptep_clear_flush()
for hugetlb pages not unmapped via huge_pmd_share and will take a look at
that soon.
Thanks.