On Mon, Oct 25, 2010 at 12:34:48PM +0800, KAMEZAWA Hiroyuki wrote: > On Mon, 25 Oct 2010 12:06:04 +0800 > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > > > 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. OK, I'll post a patch for it. > > > > > 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". > > > Memory offline is designed to be able to stop by Ctrl-C. And it has timeout > of 120 sec. > > I don't called as livelock. Ah sorry for overlooking that! I should really think twice..(after thinking twice) I find it's even better. Unmigratible pages will be put back to LRU. Then -EBUSY will be returned when trying to isolate it the next time. So it's an imaginary problem. 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>