[PATCHv8 09/32] thp: handle file pages in split_huge_pmd()

Kirill A. Shutemov
2016-05-12T15:50:03Z

Splitting THP PMD is simple: just unmap it as in DAX case. This way we
can avoid memory overhead on page table allocation to deposit.

It's probably a good idea to try to allocation page table with
GFP_ATOMIC in __split_huge_pmd_locked() to avoid refaulting the area,
but clearing pmd should be good enough for now.

Unlike DAX, we also remove the page from rmap and drop reference.
pmd_young() is transfered to PageReferenced().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/huge_memory.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 29ba922a9c26..df7b620afd7f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2940,10 +2940,18 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,

count_vm_event(THP_SPLIT_PMD);

- if (vma_is_dax(vma)) {
- pmd_t _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
+ if (!vma_is_anonymous(vma)) {
+ _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
if (is_huge_zero_pmd(_pmd))
put_huge_zero_page();
+ if (vma_is_dax(vma))
+ return;
+ page = pmd_page(_pmd);
+ if (!PageReferenced(page) && pmd_young(_pmd))
+ SetPageReferenced(page);
+ page_remove_rmap(page, true);
+ put_page(page);
+ add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
return;
} else if (is_huge_zero_pmd(*pmd)) {
return __split_huge_zero_page_pmd(vma, haddr, pmd);
--
2.8.1