On Mon, Oct 25, 2010 at 11:48:16AM +0800, KAMEZAWA Hiroyuki wrote: > On Mon, 25 Oct 2010 11:48:33 +0800 > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > > > On Mon, Oct 25, 2010 at 11:09:01AM +0800, KAMEZAWA Hiroyuki wrote: > > > On Mon, 25 Oct 2010 12:05:50 +0900 > > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > > > > > This changes behavior. > > > > > > > > This "ret" can be > 0 because migrate_page()'s return code is > > > > "Return: Number of pages not migrated or error code." > > > > > > > > Then, > > > > ret < 0 ===> maybe ebusy > > > > ret > 0 ===> some pages are not migrated. maybe PG_writeback or some > > > > ret == 0 ===> ok, all condition green. try next chunk soon. > > > > > > > > Then, I added "yield()" and --retrym_max for !ret cases. > > > ^^^^^^^^ > > > wrong. > > > > > > The code here does > > > > > > ret == 0 ==> ok, all condition green, try next chunk. > > > > It seems reasonable to remove the drain operations for "ret == 0" > > case. That would help large NUMA boxes noticeably I guess. > > > Maybe. > > > > ret > 0 ==> all pages are isolated but some pages cannot be migrated. maybe under I/O > > > do yield. > > > > Don't know how to deal with the possible "migration fail" pages -- > > sorry I have no idea about that situation at all. > > > > In typical case, page_count() > 0 by get_user_pages() or PG_writeback is set. > All we can do is just waiting. OK. > > Perhaps, OOM while offlining pages? > > > > I never see that..because memory offline is scheduled to be done only when > there are free memory. OK. On OOM migrate_page() will return -ENOMEM, which will be handled in the "ret < 0" case. So it will give up after some retries. migrate_page() has a comment /* Permanent failure */ when returning positive ret. So it looks safer not to retry indefinitely on the "ret > 0" case? Then it's reduced to two cases: "ret != 0, cannot make smooth progress, unconditional retries may livelock" and "ret ==0, makes some progress, safe to retry". Thanks, Fengguang -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>