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(). One thing that I really do not like about this patch (and I believe I have mentioned that previously) that you rely on callers to do the right thing. The proper fix would be to do the draining in start_isolate_page_range and remove them from callers. Also what does prevent start_isolate_page_range to work on multiple zones? At least contiguous allocator can do that in principle. So no I do not like this patch, it is not an improvement. -- Michal Hocko SUSE Labs
