thp: ksm: free swap when swapcache page is replaced

When a swapcache page is replaced by a ksm page, it's best to free that
swap immediately.

Reported-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 43bc893470b4..b5b907cb0f90 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -800,6 +800,8 @@ static int replace_page(struct vm_area_struct *vma, struct page *page,
         set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 
         page_remove_rmap(page);
+        if (!page_mapped(page))
+                try_to_free_swap(page);
         put_page(page);
 
         pte_unmap_unlock(ptep, ptl);