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mm: memcg: lookup_page_cgroup (almost) never returns NULL

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Pages have their corresponding page_cgroup descriptors set up before
they are used in userspace, and thus managed by a memory cgroup.

The only time where lookup_page_cgroup() can return NULL is in the
CONFIG_DEBUG_VM-only page sanity checking code that executes while
feeding pages into the page allocator for the first time.

Remove the NULL checks against lookup_page_cgroup() results from all
callsites where we know that corresponding page_cgroup descriptors must
be allocated, and add a comment to the callsite that actually does have
to check the return value.

[hughd@google.com: stop oops in mem_cgroup_update_page_stat()]
Signed-off-by: Johannes Weiner <jweiner@redhat.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2012-01-12 17:18:38 -08:00 committed by Linus Torvalds
parent 0e574a932d
commit cfa449461e
1 changed files with 7 additions and 4 deletions
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11
mm/memcontrol.c
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@ -1960,7 +1960,7 @@ void mem_cgroup_update_page_stat(struct page *page,
bool need_unlock = false;
unsigned long uninitialized_var(flags);
if (unlikely(!pc))
if (mem_cgroup_disabled())
return;
rcu_read_lock();
@ -2735,8 +2735,6 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
}
pc = lookup_page_cgroup(page);
BUG_ON(!pc); /* XXX: remove this and move pc lookup into commit */
ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
if (ret || !memcg)
return ret;
@ -3008,7 +3006,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
* Check if our page_cgroup is valid
*/
pc = lookup_page_cgroup(page);
if (unlikely(!pc || !PageCgroupUsed(pc)))
if (unlikely(!PageCgroupUsed(pc)))
return NULL;
lock_page_cgroup(pc);
@ -3436,6 +3434,11 @@ static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
struct page_cgroup *pc;
pc = lookup_page_cgroup(page);
/*
* Can be NULL while feeding pages into the page allocator for
* the first time, i.e. during boot or memory hotplug;
* or when mem_cgroup_disabled().
*/
if (likely(pc) && PageCgroupUsed(pc))
return pc;
return NULL;