As we don't account the swap stat number for the root_mem_cgroup anymore,
here we can just return an invalid CSS ID if there is no non-root memcg
is alive. Also, introduce memsw_accounting_users to track the number of
active non-root memcgs.
Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
CC: Glauber Costa <glommer@xxxxxxxxxxxxx>
CC: Michal Hocko <mhocko@xxxxxxx>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
CC: Johannes Weiner <hannes@xxxxxxxxxxx>
CC: Mel Gorman <mgorman@xxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: Sha Zhengju <handai.szj@xxxxxxxxxx>
---
mm/page_cgroup.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index c945254..189fbf5 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -336,6 +336,8 @@ struct swap_cgroup {
};
#define SC_PER_PAGE (PAGE_SIZE/sizeof(struct swap_cgroup))
+static atomic_t memsw_accounting_users = ATOMIC_INIT(0);
+
/*
* SwapCgroup implements "lookup" and "exchange" operations.
* In typical usage, this swap_cgroup is accessed via memcg's charge/uncharge
@@ -389,6 +391,9 @@ static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
struct page *mappage;
struct swap_cgroup *sc;
+ if (!atomic_read(&memsw_accounting_users))
+ return NULL;
+
ctrl = &swap_cgroup_ctrl[swp_type(ent)];
if (ctrlp)
*ctrlp = ctrl;
@@ -416,6 +421,8 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
unsigned short retval;
sc = lookup_swap_cgroup(ent, &ctrl);
+ if (!sc)
+ return 0;
spin_lock_irqsave(&ctrl->lock, flags);
retval = sc->id;
@@ -443,6 +450,8 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
unsigned long flags;
sc = lookup_swap_cgroup(ent, &ctrl);
+ if (!sc)
+ return 0;
spin_lock_irqsave(&ctrl->lock, flags);
old = sc->id;
@@ -460,7 +469,9 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
*/
unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
{
- return lookup_swap_cgroup(ent, NULL)->id;
+ struct swap_cgroup *sc = lookup_swap_cgroup(ent, NULL);
+
+ return sc ? sc->id : 0;
}
int swap_cgroup_swapon(int type, unsigned long max_pages)
@@ -471,6 +482,9 @@ int swap_cgroup_swapon(int type, unsigned long max_pages)
if (!do_swap_account)
return 0;
+ if (!atomic_read(&memsw_accounting_users))
+ return 0;
+
length = DIV_ROUND_UP(max_pages, SC_PER_PAGE);
ctrl = &swap_cgroup_ctrl[type];
--
1.7.9.5
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