Hi, On Thursday 06 September 2012 04:53:38 Minchan Kim wrote: > Normally, MIGRATE_ISOLATE type is used for memory-hotplug. > But it's irony type because the pages isolated would exist > as free page in free_area->free_list[MIGRATE_ISOLATE] so people > can think of it as allocatable pages but it is *never* allocatable. > It ends up confusing NR_FREE_PAGES vmstat so it would be > totally not accurate so some of place which depend on such vmstat > could reach wrong decision by the context. > > There were already report about it.[1] > [1] 702d1a6e, memory-hotplug: fix kswapd looping forever problem > > Then, there was other report which is other problem.[2] > [2] http://www.spinics.net/lists/linux-mm/msg41251.html > > I believe it can make problems in future, too. > So I hope removing such irony type by another design. > > I hope this patch solves it and let's revert [1] and doesn't need [2]. > > * Changelog v1 > * Fix from Michal's many suggestion > > Cc: Michal Nazarewicz <mina86@xxxxxxxxxx> > Cc: Mel Gorman <mel@xxxxxxxxx> > Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> > Cc: Wen Congyang <wency@xxxxxxxxxxxxxx> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > --- > It's very early version which show the concept so I still marked it with RFC. > I just tested it with simple test and works. > This patch is needed indepth review from memory-hotplug guys from fujitsu > because I saw there are lots of patches recenlty they sent to about > memory-hotplug change. Please take a look at this patch. [...] > @@ -948,8 +954,13 @@ static int move_freepages(struct zone *zone, > } > > order = page_order(page); > - list_move(&page->lru, > - &zone->free_area[order].free_list[migratetype]); > + if (migratetype != MIGRATE_ISOLATE) { > + list_move(&page->lru, > + &zone->free_area[order].free_list[migratetype]); > + } else { > + list_del(&page->lru); > + isolate_free_page(page, order); > + } > page += 1 << order; > pages_moved += 1 << order; > } Shouldn't NR_FREE_PAGES counter be decreased somewhere above? [ I can see that it is not modified in __free_pages_ok() and free_hot_cold_page() because page is still counted as non-free one but here situation is different AFAICS. ] I tested the patch locally here with CONFIG_CMA=y and it causes some major problems for CMA (multiple errors from dma_alloc_from_contiguous() about memory ranges being busy and allocation failures). [ I'm sorry that I don't know more details yet but the issue should be easily reproducible. ] Best regards, -- Bartlomiej Zolnierkiewicz Samsung Poland R&D Center -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>