The patch titled
Subject: mm, dax: check for pmd_none() after split_huge_pmd()
has been added to the -mm tree. Its filename is
mm-dax-check-for-pmd_none-after-split_huge_pmd.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-dax-check-for-pmd_none-after-split_huge_pmd.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-dax-check-for-pmd_none-after-split_huge_pmd.patch
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From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: mm, dax: check for pmd_none() after split_huge_pmd()
DAX implements split_huge_pmd() by clearing pmd. This simple approach
reduces memory overhead, as we don't need to deposit page table on huge
page mapping to make split_huge_pmd() never-fail. PTE table can be
allocated and populated later on page fault from backing store.
But one side effect is that have to check if pmd is pmd_none() after
split_huge_pmd(). In most places we do this already to deal with parallel
MADV_DONTNEED.
But I found two call sites which is not affected by MADV_DONTNEED (due
down_write(mmap_sem)), but need to have the check to work with DAX
properly.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mprotect.c | 6 ++++--
mm/mremap.c | 2 ++
2 files changed, 6 insertions(+), 2 deletions(-)
diff -puN mm/mprotect.c~mm-dax-check-for-pmd_none-after-split_huge_pmd mm/mprotect.c
--- a/mm/mprotect.c~mm-dax-check-for-pmd_none-after-split_huge_pmd
+++ a/mm/mprotect.c
@@ -160,9 +160,11 @@ static inline unsigned long change_pmd_r
}
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
- if (next - addr != HPAGE_PMD_SIZE)
+ if (next - addr != HPAGE_PMD_SIZE) {
split_huge_pmd(vma, pmd, addr);
- else {
+ if (pmd_none(*pmd))
+ continue;
+ } else {
int nr_ptes = change_huge_pmd(vma, pmd, addr,
newprot, prot_numa);
diff -puN mm/mremap.c~mm-dax-check-for-pmd_none-after-split_huge_pmd mm/mremap.c
--- a/mm/mremap.c~mm-dax-check-for-pmd_none-after-split_huge_pmd
+++ a/mm/mremap.c
@@ -210,6 +210,8 @@ unsigned long move_page_tables(struct vm
}
}
split_huge_pmd(vma, old_pmd, old_addr);
+ if (pmd_none(*old_pmd))
+ continue;
VM_BUG_ON(pmd_trans_huge(*old_pmd));
}
if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
mm-dax-check-for-pmd_none-after-split_huge_pmd.patch
ipc-shm-handle-removed-segments-gracefully-in-shm_mmap.patch
thp-cleanup-split_huge_page.patch
mm-make-swapin-readahead-to-improve-thp-collapse-rate-fix.patch
mm-make-swapin-readahead-to-improve-thp-collapse-rate-fix-2.patch
mm-make-swapin-readahead-to-improve-thp-collapse-rate-fix-3.patch
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