On Wed 23-11-11 16:42:27, Johannes Weiner wrote: > 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 > 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. OK, shouldn't we add diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c index 2d123f9..cb93f64 100644 --- a/mm/page_cgroup.c +++ b/mm/page_cgroup.c @@ -35,8 +35,7 @@ struct page_cgroup *lookup_page_cgroup(struct page *page) struct page_cgroup *base; base = NODE_DATA(page_to_nid(page))->node_page_cgroup; - if (unlikely(!base)) - return NULL; + BUG_ON(!base); offset = pfn - NODE_DATA(page_to_nid(page))->node_start_pfn; return base + offset; @@ -112,8 +111,7 @@ struct page_cgroup *lookup_page_cgroup(struct page *page) unsigned long pfn = page_to_pfn(page); struct mem_section *section = __pfn_to_section(pfn); - if (!section->page_cgroup) - return NULL; + BUG_ON(!section->page_cgroup); return section->page_cgroup + pfn; } just to make it explicit? > > Signed-off-by: Johannes Weiner <jweiner@xxxxxxxxxx> Other than that Acked-by: Michal Hocko <mhocko@xxxxxxx> > --- > mm/memcontrol.c | 8 ++------ > 1 files changed, 2 insertions(+), 6 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d825af9..d4d139a 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 +3321,7 @@ static struct page_cgroup *lookup_page_cgroup_used(struct page *page) > struct page_cgroup *pc; > > pc = lookup_page_cgroup(page); > + /* Can be NULL while bootstrapping the page allocator */ > if (likely(pc) && PageCgroupUsed(pc)) > return pc; > return NULL; > -- > 1.7.6.4 > -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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>