Commit 654a0dd0 authored Jan 15, 2016 by Tejun Heo Committed by Linus Torvalds Jan 15, 2016

cgroup, memcg, writeback: drop spurious rcu locking around mem_cgroup_css_from_page()



In earlier versions, mem_cgroup_css_from_page() could return non-root
css on a legacy hierarchy which can go away and required rcu locking;
however, the eventual version simply returns the root cgroup if memcg is
on a legacy hierarchy and thus doesn't need rcu locking around or in it.
Remove spurious rcu lockings.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 6f8d2b8a

fs/fs-writeback.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -677,9 +677,7 @@ void wbc_account_io(struct writeback_control wbc, struct page page,
		if (!wbc->wb)
		return;

		rcu_read_lock();
		id = mem_cgroup_css_from_page(page)->id;
		rcu_read_unlock();

		if (id == wbc->wb_id) {
		wbc->wb_bytes += bytes;

mm/memcontrol.c

+0 −3

Original line number	Diff line number	Diff line
		@@ -382,14 +382,11 @@ struct cgroup_subsys_state mem_cgroup_css_from_page(struct page page)
		{
		struct mem_cgroup *memcg;

		rcu_read_lock();

		memcg = page->mem_cgroup;

		if (!memcg \|\| !cgroup_subsys_on_dfl(memory_cgrp_subsys))
		memcg = root_mem_cgroup;

		rcu_read_unlock();
		return &memcg->css;
		}

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