On Wed, Dec 19, 2018 at 10:51:10AM +0100, Michal Hocko wrote: > On Wed 19-12-18 04:46:56, Wei Yang wrote: > > Below is a brief call flow for __offline_pages() and > > alloc_contig_range(): > > > > __offline_pages()/alloc_contig_range() > > start_isolate_page_range() > > set_migratetype_isolate() > > drain_all_pages() > > drain_all_pages() > > > > Current logic is: isolate and drain pcp list for each pageblock and > > drain pcp list again. This is not necessary and we could just drain pcp > > list once after isolate this whole range. > > > > The reason is start_isolate_page_range() will set the migrate type of > > a range to MIGRATE_ISOLATE. After doing so, this range will never be > > allocated from Buddy, neither to a real user nor to pcp list. > > But it is important to note that those pages still can be allocated from > the pcp lists until we do drain_all_pages(). I had the same fear, but then I saw that move_freepages_block()->move_freepages() moves the pages to a new list: <-- list_move(&page->lru, &zone->free_area[order].free_list[migratetype]); --> But looking at it again, I see that this is only for BuddyPages, so I guess that pcp-pages do not really get unlinked, so we could still allocate them. Uhmf, I missed that. -- Oscar Salvador SUSE L3
