Yes, we discussed this a few months ago: it's a welcome catch, but not
very serious, since it's normal for some pages to evade swap freeing,
then eventually memory pressure sorts it all out in __remove_mapping().
We did ask you back then to send in a fix separate from THP, but both
sides then forgot about it until recently.
We didn't agree on what the fix should look like. You're keen to change
the page locking there, I didn't make a persuasive case for keeping it
as is, yet I can see no point whatever in changing it for this swap fix.
Could I persuade you to approve this simpler alternative?
[PATCH] 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>
---
mm/ksm.c | 2 ++
1 file changed, 2 insertions(+)
--- 2.6.37-rc1/mm/ksm.c 2010-10-20 13:30:22.000000000 -0700
+++ linux/mm/ksm.c 2010-11-09 23:01:24.000000000 -0800
@@ -800,6 +800,8 @@ static int replace_page(struct vm_area_s
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);
--
