On Mon, 20 Feb 2012 15:35:38 -0800 (PST) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > With mem_cgroup_reset_uncharged_to_root() now making sure that freed > pages point to root_mem_cgroup (instead of to a stale and perhaps > long-deleted memcg), we no longer need to initialize page memcg to > root in those odd places which put a page on lru before charging. > Delete mem_cgroup_reset_owner(). > > But: we have no init_page_cgroup() nowadays (and even when we had, > it was called before root_mem_cgroup had been allocated); so until > a struct page has once entered the memcg lru cycle, its page_cgroup > ->mem_cgroup will be NULL instead of root_mem_cgroup. > > That could be fixed by reintroducing init_page_cgroup(), and ordering > properly: in future we shall probably want root_mem_cgroup in kernel > bss or data like swapper_space; but let's not get into that right now. > > Instead allow for this in page_relock_lruvec(): treating NULL as > root_mem_cgroup, and correcting pc->mem_cgroup before going further. > > What? Before even taking the zone->lru_lock? Is that safe? > Yes, because compaction and lumpy reclaim use __isolate_lru_page(), > which refuses unless it sees PageLRU - which may be cleared at any > instant, but we only need it to have been set once in the past for > pc->mem_cgroup to be initialized properly. > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Ok, this seems to be much better than current reset_owner(). Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Thanks, -Kame -- 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>