On Wed, Dec 19, 2018 at 02:40:56PM +0100, Michal Hocko wrote: >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. The comment is not on set_migratetype_isolate, but for its two (grandparent) callers: __offline_pages alloc_contig_range >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me
