On Tue, 21 Feb 2012, KAMEZAWA Hiroyuki wrote: > On Mon, 20 Feb 2012 15:34:28 -0800 (PST) > Hugh Dickins <hughd@xxxxxxxxxx> wrote: > return NULL; > > > > + lruvec = page_lock_lruvec(page); > > lock_page_cgroup(pc); > > > > Do we need to take lrulock+irq disable per page in this very very hot path ? I'm sure we don't want to: I hope you were pleased to find it goes away (from most cases) a couple of patches later. I had lruvec lock nested inside page_cgroup lock in the rollup I sent in December, whereas you went for page_cgroup lock nested inside lruvec lock in your lrucare patch. I couldn't find an imperative reason why they should be one way round or the other, so I tried hard to stick with your ordering, and it did work (in this 6/10). But then I couldn't work out how to get rid of the overheads added in doing it this way round, so swapped them back. > > Hmm.... How about adding NR_ISOLATED counter into lruvec ? > > Then, we can delay freeing lruvec until all conunters goes down to zero. > as... > > bool we_can_free_lruvec = true; > > lock_lruvec(lruvec->lock); > for_each_lru_lruvec(lru) > if (!list_empty(&lruvec->lru[lru])) > we_can_free_lruvec = false; > if (lruvec->nr_isolated) > we_can_free_lruvec = false; > unlock_lruvec(lruvec) > if (we_can_free_lruvec) > kfree(lruvec); > > If compaction, lumpy reclaim free a page taken from LRU, > it knows what it does and can decrement lruvec->nr_isolated properly > (it seems zone's NR_ISOLATED is decremented at putback.) At the moment I'm thinking that what we end up with by 9/10 is better than adding such a refcount. But I'm not entirely happy with mem_cgroup_reset_uncharged_to_root (it adds a further page_cgroup lookup just after I got rid of some others), and need yet to think about the race which Konstantin posits, so all options remain open. Hugh -- 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>