mm: memcg: only check anon swapin page charges for swap cache

shmem knows for sure that the page is in swap cache when attempting to
charge a page, because the cache charge entry function has a check for it.
Only anon pages may be removed from swap cache already when trying to
charge their swapin.

Adjust the comment, though: '4969c11 mm: fix swapin race condition' added
a stable PageSwapCache check under the page lock in the do_swap_page()
before calling the memory controller, so it's unuse_pte()'s pte_same()
that may fail.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Wanpeng Li <liwp.linux@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 8 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1a2020d72ca0..b06833f2b89e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2818,14 +2818,6 @@ static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm,
                 return 0;
         if (!do_swap_account)
                 goto charge_cur_mm;
-        /*
-         * A racing thread's fault, or swapoff, may have already updated
-         * the pte, and even removed page from swap cache: in those cases
-         * do_swap_page()'s pte_same() test will fail; but there's also a
-         * KSM case which does need to charge the page.
-         */
-        if (!PageSwapCache(page))
-                goto charge_cur_mm;
         memcg = try_get_mem_cgroup_from_page(page);
         if (!memcg)
                 goto charge_cur_mm;
@@ -2848,6 +2840,20 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page,
         *memcgp = NULL;
         if (mem_cgroup_disabled())
                 return 0;
+        /*
+         * A racing thread's fault, or swapoff, may have already
+         * updated the pte, and even removed page from swap cache: in
+         * those cases unuse_pte()'s pte_same() test will fail; but
+         * there's also a KSM case which does need to charge the page.
+         */
+        if (!PageSwapCache(page)) {
+                int ret;
+
+                ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, memcgp, true);
+                if (ret == -EINTR)
+                        ret = 0;
+                return ret;
+        }
         return __mem_cgroup_try_charge_swapin(mm, page, gfp_mask, memcgp);
 }