From: Johannes Weiner <jweiner@xxxxxxxxxx> 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. Signed-off-by: Johannes Weiner <jweiner@xxxxxxxxxx> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxx> --- mm/memcontrol.c | 11 +++++------ 1 files changed, 5 insertions(+), 6 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d825af9..8ccb342 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1894,9 +1894,6 @@ void mem_cgroup_update_page_stat(struct page *page, bool need_unlock = false; unsigned long uninitialized_var(flags); - if (unlikely(!pc)) - return; - rcu_read_lock(); memcg = pc->mem_cgroup; if (unlikely(!memcg || !PageCgroupUsed(pc))) @@ -2669,8 +2666,6 @@ 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; @@ -2942,7 +2937,7 @@ __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); @@ -3326,6 +3321,10 @@ 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. + */ if (likely(pc) && PageCgroupUsed(pc)) return pc; return NULL; -- 1.7.6.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>