[PATCHv4 10/25] thp: handle file COW faults

From: Kirill A. Shutemov
Date: Fri Mar 11 2016 - 18:06:45 EST

File COW for THP is handled on pte level: just split the pmd.

It's not clear how benefitial would be allocation of huge pages on COW
faults. And it would require some code to make them work.

I think at some point we can consider teaching khugepaged to collapse
pages in COW mappings, but allocating huge on fault is probably

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
mm/memory.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index f7a73b6cabac..c0a2510b9e15 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3366,6 +3366,11 @@ static int wp_huge_pmd(struct fault_env *fe, pmd_t orig_pmd)
if (fe->vma->vm_ops->pmd_fault)
return fe->vma->vm_ops->pmd_fault(fe->vma, fe->address, fe->pmd,
+ /* COW handled on pte level: split pmd */
+ VM_BUG_ON_VMA(fe->vma->vm_flags & VM_SHARED, fe->vma);
+ split_huge_pmd(fe->vma, fe->pmd, fe->address);