[PATCH 11/10] blkcg: reduce stack usage of blkg_rwstat_recursive_sum()

Tejun Heo
2015-07-16T15:55:09Z

>From 8c6417cb56c71efd47d28d15bc117567f3171c93 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Thu, 16 Jul 2015 11:50:49 -0400

The recent percpu conversion of blkg_rwstat triggered the following
warning in certain configurations.

block/blk-cgroup.c:654:1: warning: the frame size of 1360 bytes is larger than 1024 bytes

This is because blkg_rwstat now contains four percpu_counter which can
be pretty big depending on debug options although it shouldn't be a
problem in production configs. This patch removes one of the two
local blkg_rwstat variables used by blkg_rwstat_recursive_sum() to
reduce stack usage.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Link: http://article.gmane.org/gmane.linux.kernel.cgroups/13835
---
Hello,

One extra patch to deal with stack usage bloat under debug configs
which came with percpu_counter conversion. git branch updated
accordingly.

Thanks.

block/blk-cgroup.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 2469a65..0d5b8b8 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -744,7 +744,7 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,

rcu_read_lock();
blkg_for_each_descendant_pre(pos_blkg, pos_css, blkg) {
- struct blkg_rwstat *rwstat, tmp;
+ struct blkg_rwstat *rwstat;

if (!pos_blkg->online)
continue;
@@ -754,12 +754,10 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
else
rwstat = (void *)pos_blkg + off;

- tmp = blkg_rwstat_read(rwstat);
-
for (i = 0; i < BLKG_RWSTAT_NR; i++)
- atomic64_add(atomic64_read(&tmp.aux_cnt[i]) +
- atomic64_read(&rwstat->aux_cnt[i]),
- &sum.aux_cnt[i]);
+ atomic64_add(atomic64_read(&rwstat->aux_cnt[i]) +
+ percpu_counter_sum_positive(&rwstat->cpu_cnt[i]),
+ &sum.aux_cnt[i]);
}
rcu_read_unlock();

--
2.4.3