On Tue, May 24, 2011 at 06:40:31PM +0900, KOSAKI Motohiro wrote: > (2011/05/24 18:16), Mel Gorman wrote: > > On Tue, May 24, 2011 at 06:05:59PM +0900, KOSAKI Motohiro wrote: > >>>>> Why? > >>>> > >>>> Otherwise, we don't have good PCP dropping trigger. Big machine might have > >>>> big pcp cache. > >>>> > >>> > >>> Big machines also have a large cost for sending IPIs. > >> > >> Yes. But it's only matter if IPIs are frequently happen. > >> But, drain_all_pages() is NOT only IPI source. some vmscan function (e.g. > >> try_to_umap) makes a lot of IPIs. > >> > >> Then, it's _relatively_ not costly. I have a question. Do you compare which > >> operation and drain_all_pages()? IOW, your "costly" mean which scenario suspect? > >> > > > > I am concerned that if the machine gets into trouble and we are failing > > to reclaim that sending more IPIs is not going to help any. There is no > > evidence at the moment that sending extra IPIs here will help anything. > > In old days, we always call drain_all_pages() if did_some_progress!=0. But > current kernel only call it when get_page_from_freelist() fail. So, > wait_iff_congested() may help but no guarantee to help us. > > If you still strongly worry about IPI cost, I'm concern to move drain_all_pages() > to more unfrequently point. but to ignore pcp makes less sense, IMHO. > Yes, I'm worried about it because excessive time spent in drain_all_pages() has come up on the past http://lkml.org/lkml/2010/8/23/81 . The PCP lists are not being ignored at the moment. They are drained when direct reclaim makes forward progress but still fails to allocate a page. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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>