memcg: reduce check for softlimit excess

In charge/uncharge/reclaim path, usage_in_excess is calculated repeatedly
and it takes res_counter's spin_lock every time.

This patch removes unnecessary calls for res_count_soft_limit_excess.

Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 16 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1ae8c439584a..f99f5991d6bb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -313,7 +313,8 @@ soft_limit_tree_from_page(struct page *page)
 static void
 __mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
                                 struct mem_cgroup_per_zone *mz,
-                                struct mem_cgroup_tree_per_zone *mctz)
+                                struct mem_cgroup_tree_per_zone *mctz,
+                                unsigned long long new_usage_in_excess)
 {
         struct rb_node **p = &mctz->rb_root.rb_node;
         struct rb_node *parent = NULL;
@@ -322,7 +323,9 @@ __mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
         if (mz->on_tree)
                 return;
 
-        mz->usage_in_excess = res_counter_soft_limit_excess(&mem->res);
+        mz->usage_in_excess = new_usage_in_excess;
+        if (!mz->usage_in_excess)
+                return;
         while (*p) {
                 parent = *p;
                 mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
@@ -382,7 +385,7 @@ static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem)
 
 static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
 {
-        unsigned long long new_usage_in_excess;
+        unsigned long long excess;
         struct mem_cgroup_per_zone *mz;
         struct mem_cgroup_tree_per_zone *mctz;
         int nid = page_to_nid(page);
@@ -395,25 +398,21 @@ static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
          */
         for (; mem; mem = parent_mem_cgroup(mem)) {
                 mz = mem_cgroup_zoneinfo(mem, nid, zid);
-                new_usage_in_excess =
-                        res_counter_soft_limit_excess(&mem->res);
+                excess = res_counter_soft_limit_excess(&mem->res);
                 /*
                  * We have to update the tree if mz is on RB-tree or
                  * mem is over its softlimit.
                  */
-                if (new_usage_in_excess || mz->on_tree) {
+                if (excess || mz->on_tree) {
                         spin_lock(&mctz->lock);
                         /* if on-tree, remove it */
                         if (mz->on_tree)
                                 __mem_cgroup_remove_exceeded(mem, mz, mctz);
                         /*
-                         * if over soft limit, insert again. mz->usage_in_excess
-                         * will be updated properly.
+                         * Insert again. mz->usage_in_excess will be updated.
+                         * If excess is 0, no tree ops.
                          */
-                        if (new_usage_in_excess)
-                                __mem_cgroup_insert_exceeded(mem, mz, mctz);
-                        else
-                                mz->usage_in_excess = 0;
+                        __mem_cgroup_insert_exceeded(mem, mz, mctz, excess);
                         spin_unlock(&mctz->lock);
                 }
         }
@@ -2221,6 +2220,7 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
         unsigned long reclaimed;
         int loop = 0;
         struct mem_cgroup_tree_per_zone *mctz;
+        unsigned long long excess;
 
         if (order > 0)
                 return 0;
@@ -2272,9 +2272,8 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
                                         break;
                         } while (1);
                 }
-                mz->usage_in_excess =
-                        res_counter_soft_limit_excess(&mz->mem->res);
                 __mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
+                excess = res_counter_soft_limit_excess(&mz->mem->res);
                 /*
                  * One school of thought says that we should not add
                  * back the node to the tree if reclaim returns 0.
@@ -2283,8 +2282,8 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
                  * memory to reclaim from. Consider this as a longer
                  * term TODO.
                  */
-                if (mz->usage_in_excess)
-                        __mem_cgroup_insert_exceeded(mz->mem, mz, mctz);
+                /* If excess == 0, no tree ops */
+                __mem_cgroup_insert_exceeded(mz->mem, mz, mctz, excess);
                 spin_unlock(&mctz->lock);
                 css_put(&mz->mem->css);
                 loop++;