[PATCH] memcg: set page->private before calling swap_readpage

[Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>]

The function swap_readpage() (and other functions it call) extracts swap
entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
skips the swapcache and thus we need to manually set the page->private
with the swap entry before calling swap_readpage().

Signed-off-by: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Reported-by: Heiko Carstens <hca-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
---

Andrew, please squash this into "memcg: charge before adding to
swapcache on swapin" patch.

 mm/memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index aefd158ae1ea..b6f3410b5902 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 					workingset_refault(page, shadow);
 
 				lru_cache_add(page);
+
+				/* To provide entry to swap_readpage() */
+				set_page_private(page, entry.val);
 				swap_readpage(page, true);
+				set_page_private(page, 0);
 			}
 		} else {
 			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
-- 
2.31.0.rc2.261.g7f71774620-goog