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| author | Tejun Heo <tj@kernel.org> | 2012-11-05 09:16:58 -0800 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2012-11-05 09:16:58 -0800 |
| commit | e93160803ffda2e67d9ff9cacb63bb6868c8398f (patch) | |
| tree | e3305bb56336c32862f1970882f030caca7f11b2 /mm/memcontrol.c | |
| parent | ed95779340b50e362245c81b5dec0d11a1debfa8 (diff) | |
| download | blackbird-op-linux-e93160803ffda2e67d9ff9cacb63bb6868c8398f.tar.gz blackbird-op-linux-e93160803ffda2e67d9ff9cacb63bb6868c8398f.zip | |
cgroup: kill CSS_REMOVED
CSS_REMOVED is one of the several contortions which were necessary to
support css reference draining on cgroup removal. All css->refcnts
which need draining should be deactivated and verified to equal zero
atomically w.r.t. css_tryget(). If any one isn't zero, all refcnts
needed to be re-activated and css_tryget() shouldn't fail in the
process.
This was achieved by letting css_tryget() busy-loop until either the
refcnt is reactivated (failed removal attempt) or CSS_REMOVED is set
(committing to removal).
Now that css refcnt draining is no longer used, there's no need for
atomic rollback mechanism. css_tryget() simply can look at the
reference count and fail if it's deactivated - it's never getting
re-activated.
This patch removes CSS_REMOVED and updates __css_tryget() to fail if
the refcnt is deactivated. As deactivation and removal are a single
step now, they no longer need to be protected against css_tryget()
happening from irq context. Remove local_irq_disable/enable() from
cgroup_rmdir().
Note that this removes css_is_removed() whose only user is VM_BUG_ON()
in memcontrol.c. We can replace it with a check on the refcnt but
given that the only use case is a debug assert, I think it's better to
simply unexport it.
v2: Comment updated and explanation on local_irq_disable/enable()
added per Michal Hocko.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Diffstat (limited to 'mm/memcontrol.c')
| -rw-r--r-- | mm/memcontrol.c | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5a1d584ffed3..37c356646544 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2343,7 +2343,6 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, again: if (*ptr) { /* css should be a valid one */ memcg = *ptr; - VM_BUG_ON(css_is_removed(&memcg->css)); if (mem_cgroup_is_root(memcg)) goto done; if (nr_pages == 1 && consume_stock(memcg)) @@ -2483,9 +2482,9 @@ static void __mem_cgroup_cancel_local_charge(struct mem_cgroup *memcg, /* * A helper function to get mem_cgroup from ID. must be called under - * rcu_read_lock(). The caller must check css_is_removed() or some if - * it's concern. (dropping refcnt from swap can be called against removed - * memcg.) + * rcu_read_lock(). The caller is responsible for calling css_tryget if + * the mem_cgroup is used for charging. (dropping refcnt from swap can be + * called against removed memcg.) */ static struct mem_cgroup *mem_cgroup_lookup(unsigned short id) { |
