linux-kernel - [PATCH 11/10] blkcg: reduce stack usage of blkg_rwstat_recursive

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Date:	Thu, 16 Jul 2015 11:55:02 -0400
From:	Tejun Heo <tj@...nel.org>
To:	axboe@...nel.dk
Cc:	linux-kernel@...r.kernel.org, kernel-team@...com,
	vgoyal@...hat.com, avanzini.arianna@...il.com
Subject: [PATCH 11/10] blkcg: reduce stack usage of
 blkg_rwstat_recursive_sum()

>From 8c6417cb56c71efd47d28d15bc117567f3171c93 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@...nel.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@...nel.org>
Cc: Vivek Goyal <vgoyal@...hat.com>
Reported-by: kbuild test robot <fengguang.wu@...el.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

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