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>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1ae8c43..f99f599 100644 (file)
--- 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++;