thp: handle file COW faults
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
overkill.
Link: http://lkml.kernel.org/r/1466021202-61880-16-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory.c b/mm/memory.c
index 10a424e..8f42547 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3446,6 +3446,11 @@
if (fe->vma->vm_ops->pmd_fault)
return fe->vma->vm_ops->pmd_fault(fe->vma, fe->address, fe->pmd,
fe->flags);
+
+ /* 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);
+
return VM_FAULT_FALLBACK;
}