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>
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@ -1960,7 +1960,7 @@ void mem_cgroup_update_page_stat(struct page *page,
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bool need_unlock = false;
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bool need_unlock = false;
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unsigned long uninitialized_var(flags);
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unsigned long uninitialized_var(flags);
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if (unlikely(!pc))
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if (mem_cgroup_disabled())
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return;
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return;
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rcu_read_lock();
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rcu_read_lock();
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@ -2735,8 +2735,6 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
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}
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}
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pc = lookup_page_cgroup(page);
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pc = lookup_page_cgroup(page);
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BUG_ON(!pc); /* XXX: remove this and move pc lookup into commit */
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ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
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ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
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if (ret || !memcg)
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if (ret || !memcg)
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return ret;
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return ret;
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@ -3008,7 +3006,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
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* Check if our page_cgroup is valid
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* Check if our page_cgroup is valid
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*/
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*/
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pc = lookup_page_cgroup(page);
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pc = lookup_page_cgroup(page);
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if (unlikely(!pc || !PageCgroupUsed(pc)))
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if (unlikely(!PageCgroupUsed(pc)))
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return NULL;
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return NULL;
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lock_page_cgroup(pc);
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lock_page_cgroup(pc);
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@ -3436,6 +3434,11 @@ static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
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struct page_cgroup *pc;
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struct page_cgroup *pc;
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pc = lookup_page_cgroup(page);
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pc = lookup_page_cgroup(page);
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/*
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* Can be NULL while feeding pages into the page allocator for
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* the first time, i.e. during boot or memory hotplug;
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* or when mem_cgroup_disabled().
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*/
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if (likely(pc) && PageCgroupUsed(pc))
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if (likely(pc) && PageCgroupUsed(pc))
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return pc;
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return pc;
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return NULL;
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return NULL;
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