cgroup: move rstat base stat objects into their own struct

This non-functional change serves as preparation for moving to
subsystem-based rstat trees. The base stats are not an actual subsystem,
but in future commits they will have exclusive rstat trees just as other
subsystems will.

Moving the base stat objects into a new struct allows the cgroup_rstat_cpu
struct to become more compact since it now only contains the minimum amount
of pointers needed for rstat participation. Subsystems will (in future
commits) make use of the compact cgroup_rstat_cpu struct while avoiding the
memory overhead of the base stat objects which they will not use.

An instance of the new struct cgroup_rstat_base_cpu was placed on the
cgroup struct so it can retain ownership of these base stats common to all
cgroups. A helper function was added for looking up the cpu-specific base
stats of a given cgroup. Finally, initialization and variable names were
adjusted where applicable.

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 22 insertions, 16 deletions

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 5bc8f55c8cca..1bf2e8db6dac 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -344,11 +344,30 @@ struct cgroup_base_stat {
  * frequency decreases the cost of each read.
  *
  * This struct hosts both the fields which implement the above -
- * updated_children and updated_next - and the fields which track basic
- * resource statistics on top of it - bsync, bstat and last_bstat.
+ * updated_children and updated_next.
  */
 struct cgroup_rstat_cpu {
 	/*
+	 * Child cgroups with stat updates on this cpu since the last read
+	 * are linked on the parent's ->updated_children through
+	 * ->updated_next.
+	 *
+	 * In addition to being more compact, singly-linked list pointing
+	 * to the cgroup makes it unnecessary for each per-cpu struct to
+	 * point back to the associated cgroup.
+	 *
+	 * Protected by per-cpu cgroup_rstat_cpu_lock.
+	 */
+	struct cgroup *updated_children;	/* terminated by self cgroup */
+	struct cgroup *updated_next;		/* NULL iff not on the list */
+};
+
+/*
+ * This struct hosts the fields which track basic resource statistics on
+ * top of it - bsync, bstat and last_bstat.
+ */
+struct cgroup_rstat_base_cpu {
+	/*
 	 * ->bsync protects ->bstat.  These are the only fields which get
 	 * updated in the hot path.
 	 */
@@ -374,20 +393,6 @@ struct cgroup_rstat_cpu {
 	 * deltas to propagate to the per-cpu subtree_bstat.
 	 */
 	struct cgroup_base_stat last_subtree_bstat;
-
-	/*
-	 * Child cgroups with stat updates on this cpu since the last read
-	 * are linked on the parent's ->updated_children through
-	 * ->updated_next.
-	 *
-	 * In addition to being more compact, singly-linked list pointing
-	 * to the cgroup makes it unnecessary for each per-cpu struct to
-	 * point back to the associated cgroup.
-	 *
-	 * Protected by per-cpu cgroup_rstat_cpu_lock.
-	 */
-	struct cgroup *updated_children;	/* terminated by self cgroup */
-	struct cgroup *updated_next;		/* NULL iff not on the list */
 };
 
 struct cgroup_freezer_state {
@@ -518,6 +523,7 @@ struct cgroup {
 
 	/* per-cpu recursive resource statistics */
 	struct cgroup_rstat_cpu __percpu *rstat_cpu;
+	struct cgroup_rstat_base_cpu __percpu *rstat_base_cpu;
 	struct list_head rstat_css_list;
 
 	/*