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

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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>
This commit is contained in:
Tejun Heo 2016-01-15 16:57:16 -08:00 • committed by Linus Torvalds
parent 6f8d2b8a26
commit 654a0dd095
2 changed files with 0 additions and 5 deletions
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2
fs/fs-writeback.c
View file

@ -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;

3
mm/memcontrol.c
View file

@ -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;
}