mem/memcg: cache rightmost node

Such that we can optimize __mem_cgroup_largest_soft_limit_node().  The
only overhead is the extra footprint for the cached pointer, but this
should not be an issue for mem_cgroup_tree_per_node.

[dave@stgolabs.net: brain fart #2]
Link: http://lkml.kernel.org/r/20170731160114.GE21328@linux-80c1.suse
Link: http://lkml.kernel.org/r/20170719014603.19029-17-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.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 ca83f38..15af3da 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -119,6 +119,7 @@ static const char *const mem_cgroup_lru_names[] = {
 
 struct mem_cgroup_tree_per_node {
        struct rb_root rb_root;
+       struct rb_node *rb_rightmost;
        spinlock_t lock;
 };
 
@@ -386,6 +387,7 @@ static void __mem_cgroup_insert_exceeded(struct mem_cgroup_per_node *mz,
        struct rb_node **p = &mctz->rb_root.rb_node;
        struct rb_node *parent = NULL;
        struct mem_cgroup_per_node *mz_node;
+       bool rightmost = true;
 
        if (mz->on_tree)
                return;
@@ -397,8 +399,11 @@ static void __mem_cgroup_insert_exceeded(struct mem_cgroup_per_node *mz,
                parent = *p;
                mz_node = rb_entry(parent, struct mem_cgroup_per_node,
                                        tree_node);
-               if (mz->usage_in_excess < mz_node->usage_in_excess)
+               if (mz->usage_in_excess < mz_node->usage_in_excess) {
                        p = &(*p)->rb_left;
+                       rightmost = false;
+               }
+
                /*
                 * We can't avoid mem cgroups that are over their soft
                 * limit by the same amount
@@ -406,6 +411,10 @@ static void __mem_cgroup_insert_exceeded(struct mem_cgroup_per_node *mz,
                else if (mz->usage_in_excess >= mz_node->usage_in_excess)
                        p = &(*p)->rb_right;
        }
+
+       if (rightmost)
+               mctz->rb_rightmost = &mz->tree_node;
+
        rb_link_node(&mz->tree_node, parent, p);
        rb_insert_color(&mz->tree_node, &mctz->rb_root);
        mz->on_tree = true;
@@ -416,6 +425,10 @@ static void __mem_cgroup_remove_exceeded(struct mem_cgroup_per_node *mz,
 {
        if (!mz->on_tree)
                return;
+
+       if (&mz->tree_node == mctz->rb_rightmost)
+               mctz->rb_rightmost = rb_prev(&mz->tree_node);
+
        rb_erase(&mz->tree_node, &mctz->rb_root);
        mz->on_tree = false;
 }
@@ -496,16 +509,15 @@ static void mem_cgroup_remove_from_trees(struct mem_cgroup *memcg)
 static struct mem_cgroup_per_node *
 __mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_node *mctz)
 {
-       struct rb_node *rightmost = NULL;
        struct mem_cgroup_per_node *mz;
 
 retry:
        mz = NULL;
-       rightmost = rb_last(&mctz->rb_root);
-       if (!rightmost)
+       if (!mctz->rb_rightmost)
                goto done;              /* Nothing to reclaim from */
 
-       mz = rb_entry(rightmost, struct mem_cgroup_per_node, tree_node);
+       mz = rb_entry(mctz->rb_rightmost,
+                     struct mem_cgroup_per_node, tree_node);
        /*
         * Remove the node now but someone else can add it back,
         * we will to add it back at the end of reclaim to its correct
@@ -5945,6 +5957,7 @@ static int __init mem_cgroup_init(void)
                                    node_online(node) ? node : NUMA_NO_NODE);
 
                rtpn->rb_root = RB_ROOT;
+               rtpn->rb_rightmost = NULL;
                spin_lock_init(&rtpn->lock);
                soft_limit_tree.rb_tree_per_node[node] = rtpn;
        }