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.
Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
---
mm/memory.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/mm/memory.c b/mm/memory.c
index c41804c0d524..e5c6b4387da3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3395,6 +3395,11 @@ 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,
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;
}
--
2.8.0.rc3
