mm/memcg: fix device private memcg accounting

BugLink: https://bugs.launchpad.net/bugs/1902115
[ Upstream commit 9a137153fc8798a89d8fce895cd0a06ea5b8e37c ]

The code in mc_handle_swap_pte() checks for non_swap_entry() and returns
NULL before checking is_device_private_entry() so device private pages are
never handled.  Fix this by checking for non_swap_entry() after handling
device private swap PTEs.

I assume the memory cgroup accounting would be off somehow when moving
a process to another memory cgroup.  Currently, the device private page
is charged like a normal anonymous page when allocated and is uncharged
when the page is freed so I think that path is OK.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Link: https://lkml.kernel.org/r/20201009215952.2726-1-rcampbell@nvidia.com
xFixes: c733a82874a7 ("mm/memcontrol: support MEMORY_DEVICE_PRIVATE")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Ian May <ian.may@canonical.com>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ca1632850fb76da05c9756dcff36633cee9b398a..edf98f8588eeb95259a50d6a56a0d59c6fc1dbdc 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5398,7 +5398,7 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
        struct page *page = NULL;
        swp_entry_t ent = pte_to_swp_entry(ptent);
 
-       if (!(mc.flags & MOVE_ANON) || non_swap_entry(ent))
+       if (!(mc.flags & MOVE_ANON))
                return NULL;
 
        /*
@@ -5417,6 +5417,9 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
                return page;
        }
 
+       if (non_swap_entry(ent))
+               return NULL;
+
        /*
         * Because lookup_swap_cache() updates some statistics counter,
         * we call find_get_page() with swapper_space directly.