blkcg: don't create "io.stat" on the root cgroup

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@kernel.org>
Acked-by: Jens Axboe <axboe@kernel.dk>
Cc: Vivek Goyal <vgoyal@redhat.com>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index ac8370cb25157d2ed1cd215f8b95edde0735e3de..4fa54161d423097da1441a41004ce416bf547280 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -896,6 +896,7 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)
 struct cftype blkcg_files[] = {
        {
                .name = "stat",
+               .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = blkcg_print_stat,
        },
        { }     /* terminate */