Messages in this thread | | | Date | Mon, 6 Sep 2010 11:16:33 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH 2/2] Make is_mem_section_removable more conformable with offlining code v3 |
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On Sat 04-09-10 10:55:16, Wu Fengguang wrote: > On Fri, Sep 03, 2010 at 07:42:13PM +0800, Michal Hocko wrote: > > > +/* > > + * A free or LRU pages block are removable > > + * Do not use MIGRATE_MOVABLE because it can be insufficient and > > + * other MIGRATE types are tricky. > > + * Do not hold zone->lock as this is used from user space by the > > + * sysfs interface. > > + */ > > +bool is_page_removable(struct page *page) > > +{ > > + int page_block = 1 << pageblock_order; > > + > > + /* All pages from the MOVABLE zone are movable */ > > + if (zone_idx(page_zone(page)) == ZONE_MOVABLE) > > + return true; > > + > > + while (page_block > 0) { > > + int order = 0; > > + > > + if (pfn_valid_within(page_to_pfn(page))) { > > + if (!page_count(page) && PageBuddy(page)) { > > PageBuddy() is true only for the head page and false for all tail > pages. So when is_page_removable() is given a random 4k page > (get_any_page() will exactly do that), the above test is not enough.
OK, I haven't noticed that set_migratetype_isolate (which calls is_page_removable in my patch - bellow) is called from that context. is_mem_section_removable goes by pageblocks so we are always checking the head.
Anyway, I can see why you are counting unmovable pages in your patch now. You need it for notifier logic, so my approach is not usable.
Thanks! -- Michal Hocko L3 team SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic
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