From 16b3de6652c7aef151f38726faf90f0dbc9e9c71 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Wed, 9 Jan 2013 08:05:12 -0800
Subject: [PATCH] blkcg: implement blkg_[rw]stat_recursive_sum() and
 blkg_[rw]stat_merge()

Implement blkg_[rw]stat_recursive_sum() and blkg_[rw]stat_merge().
The former two collect the [rw]stats designated by the target policy
data and offset from the pd's subtree.  The latter two add one
[rw]stat to another.

Note that the recursive sum functions require the queue lock to be
held on entry to make blkg online test reliable.  This is necessary to
properly handle stats of a dying blkg.

These will be used to implement hierarchical stats.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
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