On Wed 19-12-18 13:29:34, Wei Yang wrote: > 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(). > > > >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 > > Well, I don't really understand this meaning previously. > > So you prefer set_migratetype_isolate() do the drain instead of the > caller (__offline_pages) do the drain. Is my understanding correct? Either set_migratetype_isolate or start_isolate_page_range. The later only if this is guaranteed that we cannot intemix zones in the range. > >prevent start_isolate_page_range to work on multiple zones? At least > >contiguous allocator can do that in principle. > > As the comment mentioned, in current implementation the range must be in > one zone. I do not see anything like that documented for set_migratetype_isolate. -- Michal Hocko SUSE Labs
