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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2016-02-11 16:13:03 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-02-11 18:35:48 -0800
commit6b9116a652bd9e0e2994505cfaaa5f66deaa2a05 (patch)
tree9e9ae34807081abbec6ed856f4ed7c1f9b33d225 /mm
parent7eb391299419a03cbe0fa5ab0e6b0932e42c7a36 (diff)
downloadlinux-linaro-stable-6b9116a652bd9e0e2994505cfaaa5f66deaa2a05.tar.gz
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@linux.intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/mprotect.c6
-rw-r--r--mm/mremap.c2
2 files changed, 6 insertions, 2 deletions
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 8eb7bb40dc40..f7cb3d4d9c2e 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -160,9 +160,11 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
}
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 --git a/mm/mremap.c b/mm/mremap.c
index d77946a997f7..8eeba02fc991 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -210,6 +210,8 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
}
}
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,