From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Subject: mm/thp/pagecache/collapse: free the pte page table on collapse for thp page cache.
With THP page cache, when trying to build a huge page from regular pte
pages, we just clear the pmd entry. We will take another fault and at
that point we will find the huge page in the radix tree, thereby using the
huge page to complete the page fault
The second fault path will allocate the needed pgtable_t page for archs
like ppc64. So no need to deposit the same in collapse path. Depositing
them in the collapse path resulting in a pgtable_t memory leak also giving
errors like "[ 2362.021762] BUG: non-zero nr_ptes on freeing mm: 3"
Fixes: 953c66c2b22a304d ("mm: THP page cache support for ppc64")
Link: http://lkml.kernel.org/r/20161212163428.6780-2-aneesh.kumar@xxxxxxxxxxxxxxxxxx
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 21 ++-------------------
1 file changed, 2 insertions(+), 19 deletions(-)
diff -puN mm/khugepaged.c~mm-thp-pagecache-collapse-free-the-pte-page-table-on-collapse-for-thp-page-cache mm/khugepaged.c
--- a/mm/khugepaged.c~mm-thp-pagecache-collapse-free-the-pte-page-table-on-collapse-for-thp-page-cache
+++ a/mm/khugepaged.c
@@ -1242,7 +1242,6 @@ static void retract_page_tables(struct a
struct vm_area_struct *vma;
unsigned long addr;
pmd_t *pmd, _pmd;
- bool deposited = false;
i_mmap_lock_write(mapping);
vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
@@ -1267,26 +1266,10 @@ static void retract_page_tables(struct a
spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
/* assume page table is clear */
_pmd = pmdp_collapse_flush(vma, addr, pmd);
- /*
- * now deposit the pgtable for arch that need it
- * otherwise free it.
- */
- if (arch_needs_pgtable_deposit()) {
- /*
- * The deposit should be visibile only after
- * collapse is seen by others.
- */
- smp_wmb();
- pgtable_trans_huge_deposit(vma->vm_mm, pmd,
- pmd_pgtable(_pmd));
- deposited = true;
- }
spin_unlock(ptl);
up_write(&vma->vm_mm->mmap_sem);
- if (!deposited) {
- atomic_long_dec(&vma->vm_mm->nr_ptes);
- pte_free(vma->vm_mm, pmd_pgtable(_pmd));
- }
+ atomic_long_dec(&vma->vm_mm->nr_ptes);
+ pte_free(vma->vm_mm, pmd_pgtable(_pmd));
}
}
i_mmap_unlock_write(mapping);
_
--
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