blkcg: implement blkg_[rw]stat_recursive_sum() and blkg_[rw]stat_merge()

Implement blkg_[rw]stat_recursive_sum() and blkg_[rw]stat_merge().
The former two collect the [rw]stats designated by the target policy
data and offset from the pd's subtree.  The latter two add one
[rw]stat to another.

Note that the recursive sum functions require the queue lock to be
held on entry to make blkg online test reliable.  This is necessary to
properly handle stats of a dying blkg.

These will be used to implement hierarchical stats.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 586c0ac3309..f2b292925cc 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -164,6 +164,10 @@ u64 blkg_prfill_stat(struct seq_file *sf, struct blkg_policy_data *pd, int off);
 u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 		       int off);
 
+u64 blkg_stat_recursive_sum(struct blkg_policy_data *pd, int off);
+struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkg_policy_data *pd,
+					     int off);
+
 struct blkg_conf_ctx {
 	struct gendisk			*disk;
 	struct blkcg_gq			*blkg;
@@ -414,6 +418,18 @@ static inline void blkg_stat_reset(struct blkg_stat *stat)
 }
 
 /**
+ * blkg_stat_merge - merge a blkg_stat into another
+ * @to: the destination blkg_stat
+ * @from: the source
+ *
+ * Add @from's count to @to.
+ */
+static inline void blkg_stat_merge(struct blkg_stat *to, struct blkg_stat *from)
+{
+	blkg_stat_add(to, blkg_stat_read(from));
+}
+
+/**
  * blkg_rwstat_add - add a value to a blkg_rwstat
  * @rwstat: target blkg_rwstat
  * @rw: mask of REQ_{WRITE|SYNC}
@@ -484,6 +500,25 @@ static inline void blkg_rwstat_reset(struct blkg_rwstat *rwstat)
 	memset(rwstat->cnt, 0, sizeof(rwstat->cnt));
 }
 
+/**
+ * blkg_rwstat_merge - merge a blkg_rwstat into another
+ * @to: the destination blkg_rwstat
+ * @from: the source
+ *
+ * Add @from's counts to @to.
+ */
+static inline void blkg_rwstat_merge(struct blkg_rwstat *to,
+				     struct blkg_rwstat *from)
+{
+	struct blkg_rwstat v = blkg_rwstat_read(from);
+	int i;
+
+	u64_stats_update_begin(&to->syncp);
+	for (i = 0; i < BLKG_RWSTAT_NR; i++)
+		to->cnt[i] += v.cnt[i];
+	u64_stats_update_end(&to->syncp);
+}
+
 #else	/* CONFIG_BLK_CGROUP */
 
 struct cgroup;