memcg: make mem_cgroup_force_empty_list() return bool

mem_cgroup_force_empty_list() just returns 0 or -EBUSY and -EBUSY
indicates 'you need to retry'.  Make mem_cgroup_force_empty_list() return
a bool to simplify the logic.

[akpm@linux-foundation.org: rework mem_cgroup_force_empty_list()'s comment]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9647866..a2677e0 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3609,10 +3609,12 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 }
 
 /*
- * This routine traverse page_cgroup in given list and drop them all.
- * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
+ * Traverse a specified page_cgroup list and try to drop them all.  This doesn't
+ * reclaim the pages page themselves - it just removes the page_cgroups.
+ * Returns true if some page_cgroups were not freed, indicating that the caller
+ * must retry this operation.
  */
-static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
+static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
                                int node, int zid, enum lru_list lru)
 {
        struct mem_cgroup_per_zone *mz;
@@ -3620,7 +3622,6 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
        struct list_head *list;
        struct page *busy;
        struct zone *zone;
-       int ret = 0;
 
        zone = &NODE_DATA(node)->node_zones[zid];
        mz = mem_cgroup_zoneinfo(memcg, node, zid);
@@ -3634,7 +3635,6 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
                struct page_cgroup *pc;
                struct page *page;
 
-               ret = 0;
                spin_lock_irqsave(&zone->lru_lock, flags);
                if (list_empty(list)) {
                        spin_unlock_irqrestore(&zone->lru_lock, flags);
@@ -3651,19 +3651,14 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
 
                pc = lookup_page_cgroup(page);
 
-               ret = mem_cgroup_move_parent(page, pc, memcg);
-
-               if (ret == -EBUSY || ret == -EINVAL) {
+               if (mem_cgroup_move_parent(page, pc, memcg)) {
                        /* found lock contention or "pc" is obsolete. */
                        busy = page;
                        cond_resched();
                } else
                        busy = NULL;
        }
-
-       if (!ret && !list_empty(list))
-               return -EBUSY;
-       return ret;
+       return !list_empty(list);
 }
 
 /*