On Mon, 28 Feb 2011 09:28:14 +0000 Mel Gorman <mel@xxxxxxxxx> wrote: > On Mon, Feb 28, 2011 at 02:54:02PM +0900, KAMEZAWA Hiroyuki wrote: > > On Mon, 28 Feb 2011 06:48:18 +0100 > > Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > > > > > On Mon, Feb 28, 2011 at 11:17:46AM +0900, KAMEZAWA Hiroyuki wrote: > > > > BTW, I forget why we always take zone->lru_lock with IRQ disabled.... > > > > > > To decrease lock contention in SMP to deliver overall better > > > performance (not sure how much it helps though). It was supposed to be > > > hold for a very short time (PAGEVEC_SIZE) to avoid giving irq latency > > > problems. > > > > > > > memory hotplug uses MIGRATE_ISOLATED migrate types for scanning pfn range > > without lru_lock. I wonder whether we can make use of it (the function > > which memory hotplug may need rework for the compaction but migrate_type can > > be used, I think). > > > > I don't see how migrate_type would be of any benefit here particularly > as compaction does not directly affect the migratetype of a pageblock. I > have not checked closely which part of hotplug you are on about but if > you're talking about when pages actually get offlined, the zone lock is > not necessary there because the pages are not on the LRU. In compactions > case, they are. Did I misunderstand? > memory offline code doesn't take big lru_lock (and call isolate_lru_page()) at picking up migration target pages from LRU. While this, allocation from the zone is allowed. memory offline is done by mem_section unit. memory offline does. 1. making a whole section as MIGRATETYPE_ISOLATED. 2. scan pfn within section. 3. find a page on LRU 4. isolate_lru_page() -> take/release lru_lock. ----(*) 5. migrate it. 6. making all pages in the range as RESERVED. During this, by marking the pageblock as MIGRATETYPE_ISOLATED, - new allocation will never picks up a page in the range. - newly freed pages in the range will never be allocated and never in pcp. - page type of the range will never change. then, memory offline success. If (*) seems too heavy anyway and will be no help even if with some batching as isolate_lru_page_pagevec() or some, okay please forget offlining. BTW, can't we drop disable_irq() from all lru_lock related codes ? Thanks, -Kame -- 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>