linux-kernel - [PATCH block/for-4.4/core] blkcg: don't create "io.stat" on the root cgroup

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Message-ID: <20151022003103.GB10199@mtj.duckdns.org>
Date:	Thu, 22 Oct 2015 09:31:03 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	kernel-team@...com
Subject: [PATCH block/for-4.4/core] blkcg: don't create "io.stat" on the root
 cgroup

Hello, Jens.

This is one of hopefully final adjustments to cgroup v2 behavior
before lifting the devel mask.  If the patch is okay, can I route the
patch through cgroup/for-4.4 so that it can go together with the
cgroup documentation update patch?

Thanks.

------ 8< ------
The stat files on the root cgroup shows stats for the whole system and
usually don't contain any information which isn't available through
the usual system monitoring mechanisms.  Some controllers skip
collecting these duplicate stats to optimize cases where cgroup isn't
used and later try to emulate the result on demand.

This leads to complexities and subtle differences in the information
shown through different channels.  This is entirely unnecessary and
cgroup v2 is dropping stat files which are duplicate from all
controllers.  This patch removes "io.stat" from the root hierarchy.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Vivek Goyal <vgoyal@...hat.com>
---
 block/blk-cgroup.c |    1 +
 1 file changed, 1 insertion(+)

--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -896,6 +896,7 @@ static int blkcg_print_stat(struct seq_f
 struct cftype blkcg_files[] = {
 	{
 		.name = "stat",
+		.flags = CFTYPE_NOT_ON_ROOT,
 		.seq_show = blkcg_print_stat,
 	},
 	{ }	/* terminate */
--
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