blk-cgroup: pass blkg_rwstat structures by reference

Returning a structure generates rather bad code, so switch to passing
by reference.  Also don't require the structure to be zeroed and add
to the 0-initialized counters, but actually set the counters to the
calculated value.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 25 insertions, 21 deletions

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index b3796a40a61a..66abc82179f3 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -935,9 +935,9 @@ static u64 bfqg_prfill_stat_recursive(struct seq_file *sf,
 static u64 bfqg_prfill_rwstat_recursive(struct seq_file *sf,
                                         struct blkg_policy_data *pd, int off)
 {
-        struct blkg_rwstat sum = blkg_rwstat_recursive_sum(pd_to_blkg(pd),
-                                                           &blkcg_policy_bfq,
-                                                           off);
+        struct blkg_rwstat sum;
+
+        blkg_rwstat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_bfq, off, &sum);
         return __blkg_prfill_rwstat(sf, pd, &sum);
 }
 
@@ -975,9 +975,12 @@ static int bfqg_print_stat_sectors(struct seq_file *sf, void *v)
 static u64 bfqg_prfill_sectors_recursive(struct seq_file *sf,
                                          struct blkg_policy_data *pd, int off)
 {
-        struct blkg_rwstat tmp = blkg_rwstat_recursive_sum(pd->blkg, NULL,
-                                        offsetof(struct blkcg_gq, stat_bytes));
-        u64 sum = atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
+        struct blkg_rwstat tmp;
+        u64 sum;
+
+        blkg_rwstat_recursive_sum(pd->blkg, NULL,
+                        offsetof(struct blkcg_gq, stat_bytes), &tmp);
+        sum = atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
                 atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_WRITE]);
 
         return __blkg_prfill_u64(sf, pd, sum >> 9);
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 0778e52b1db2..db039a869d95 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -597,8 +597,9 @@ EXPORT_SYMBOL_GPL(blkg_prfill_stat);
 u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
                        int off)
 {
-        struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd + off);
+        struct blkg_rwstat rwstat = { };
 
+        blkg_rwstat_read((void *)pd + off, &rwstat);
         return __blkg_prfill_rwstat(sf, pd, &rwstat);
 }
 EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
@@ -606,8 +607,9 @@ EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
 static u64 blkg_prfill_rwstat_field(struct seq_file *sf,
                                     struct blkg_policy_data *pd, int off)
 {
-        struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd->blkg + off);
+        struct blkg_rwstat rwstat = { };
 
+        blkg_rwstat_read((void *)pd->blkg + off, &rwstat);
         return __blkg_prfill_rwstat(sf, pd, &rwstat);
 }
 
@@ -649,8 +651,9 @@ static u64 blkg_prfill_rwstat_field_recursive(struct seq_file *sf,
                                               struct blkg_policy_data *pd,
                                               int off)
 {
-        struct blkg_rwstat rwstat = blkg_rwstat_recursive_sum(pd->blkg,
-                                                              NULL, off);
+        struct blkg_rwstat rwstat;
+
+        blkg_rwstat_recursive_sum(pd->blkg, NULL, off, &rwstat);
         return __blkg_prfill_rwstat(sf, pd, &rwstat);
 }
 
@@ -731,6 +734,7 @@ EXPORT_SYMBOL_GPL(blkg_stat_recursive_sum);
  * @blkg: blkg of interest
  * @pol: blkcg_policy which contains the blkg_rwstat
  * @off: offset to the blkg_rwstat in blkg_policy_data or @blkg
+ * @sum: blkg_rwstat structure containing the results
  *
  * Collect the blkg_rwstat specified by @blkg, @pol and @off and all its
  * online descendants and their aux counts.  The caller must be holding the
@@ -739,12 +743,11 @@ EXPORT_SYMBOL_GPL(blkg_stat_recursive_sum);
  * If @pol is NULL, blkg_rwstat is at @off bytes into @blkg; otherwise, it
  * is at @off bytes into @blkg's blkg_policy_data of the policy.
  */
-struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
-                                             struct blkcg_policy *pol, int off)
+void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
+                int off, struct blkg_rwstat *sum)
 {
         struct blkcg_gq *pos_blkg;
         struct cgroup_subsys_state *pos_css;
-        struct blkg_rwstat sum = { };
         unsigned int i;
 
         lockdep_assert_held(&blkg->q->queue_lock);
@@ -762,12 +765,10 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
                         rwstat = (void *)pos_blkg + off;
 
                 for (i = 0; i < BLKG_RWSTAT_NR; i++)
-                        atomic64_add(blkg_rwstat_read_counter(rwstat, i),
-                                &sum.aux_cnt[i]);
+                        atomic64_set(&sum->aux_cnt[i],
+                                blkg_rwstat_read_counter(rwstat, i));
         }
         rcu_read_unlock();
-
-        return sum;
 }
 EXPORT_SYMBOL_GPL(blkg_rwstat_recursive_sum);
 
@@ -953,14 +954,14 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)
 
                 spin_lock_irq(&blkg->q->queue_lock);
 
-                rwstat = blkg_rwstat_recursive_sum(blkg, NULL,
-                                        offsetof(struct blkcg_gq, stat_bytes));
+                blkg_rwstat_recursive_sum(blkg, NULL,
+                                offsetof(struct blkcg_gq, stat_bytes), &rwstat);
                 rbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_READ]);
                 wbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_WRITE]);
                 dbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_DISCARD]);
 
-                rwstat = blkg_rwstat_recursive_sum(blkg, NULL,
-                                        offsetof(struct blkcg_gq, stat_ios));
+                blkg_rwstat_recursive_sum(blkg, NULL,
+                                        offsetof(struct blkcg_gq, stat_ios), &rwstat);
                 rios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_READ]);
                 wios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_WRITE]);
                 dios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_DISCARD]);