2011/6/23 Michal Hocko <mhocko@xxxxxxx>: > On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote: >> On Thu, 23 Jun 2011 11:02:04 +0200 >> Michal Hocko <mhocko@xxxxxxx> wrote: >> >> > On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote: >> > > On Thu, 23 Jun 2011 09:41:33 +0200 >> > > Michal Hocko <mhocko@xxxxxxx> wrote: >> > [...] >> > > > Other than that: >> > > > Reviewed-by: Michal Hocko <mhocko@xxxxxxx> >> > > > >> > > >> > > I found the page is added to LRU before charging. (In this case, >> > > memcg's LRU is ignored.) I'll post a new version with a fix. >> > >> > Yes, you are right. I have missed that. >> > This means that we might race with reclaim which could evict the COWed >> > page wich in turn would uncharge that page even though we haven't >> > charged it yet. >> > >> > Can we postpone page_add_new_anon_rmap to the charging path or it would >> > just race somewhere else? >> > >> >> I got a different idea. How about this ? >> I think this will have benefit for non-memcg users under OOM, too. > > Could you be more specific? I do not see how preallocation which might > turn out to be pointless could help under OOM. > We'll have no page allocation under lock_page() held in this path. I think it is good. >> >> A concerns is VM_FAULT_RETRY case but wait-for-lock will be much heavier >> than preallocation + free-for-retry cost. > > Preallocation is rather costly when fault handler fails (e.g. SIGBUS > which is the easiest one to trigger). > I think pcp cache of free page allocater does enough good job and I guess we'll see no problem even if there is a storm of SIGBUS. > I am not saying this approach is bad but I think that preallocation can > be much more costly than unlock, charge and lock&recheck approach. memcg_is_disabled() cannot help ROOT cgroup. And additional lock/unlock method may kill FAULT_RETRY at lock contention optimization which was added recently. 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>