path: root/mm
diff options
authorJohannes Weiner <jweiner@redhat.com>2012-01-12 17:18:38 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-12 20:13:06 -0800
commitcfa449461e67b60df986170eecb089831fa9e49a (patch)
treeff40cff591e27250b91b2f1fb4409875f397b048 /mm
parent0e574a932d2cab8eb3b02d21feb59f2c09154738 (diff)
mm: memcg: lookup_page_cgroup (almost) never returns NULL
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>
Diffstat (limited to 'mm')
1 files changed, 7 insertions, 4 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 93cb16d2b96a..a63ad141083c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -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())
@@ -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;
@@ -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;

Privacy Policy