On Thu, Dec 20, 2018 at 05:23:02PM +0100, Michal Hocko wrote: >On Thu 20-12-18 15:58:03, Wei Yang wrote: >> On Wed, Dec 19, 2018 at 03:39:27PM +0100, Michal Hocko wrote: >> >On Wed 19-12-18 14:33:27, Wei Yang wrote: >> >[...] >> >> Then I am confused about the objection to this patch. Finally, we drain >> >> all the pages in pcp list and the range is isolated. >> > >> >Please read my emails more carefully. As I've said, the only reason to >> >do care about draining is to remove it from where it doesn't belong. >> >> I go through the thread again and classify two main opinions from you >> and Oscar. >> >> 1) We can still allocate pages in a specific range from pcp list even we >> have already isolate this range. >> 2) We shouldn't rely on caller to drain pages and >> set_migratetype_isolate() may handle a range cross zones. >> >> I understand the second one and agree it is not proper to rely on caller >> and make the assumption on range for set_migratetype_isolate(). >> >> My confusion comes from the first one. As you and Oscar both mentioned >> this and Oscar said "I had the same fear", this makes me think current >> implementation is buggy. But your following reply said this is not. This >> means current approach works fine. >> >> If the above understanding is correct, and combining with previous >> discussion, the improvement we can do is to remove the drain_all_pages() >> in __offline_pages()/alloc_contig_range(). By doing so, the pcp list >> drain doesn't rely on caller and the isolation/drain on each pageblock >> ensures pcp list will not contain any page in this range now and future. >> This imply the drain_all_pages() in >> __offline_pages()/alloc_contig_range() is not necessary. >> >> Is my understanding correct? > >Yes Thanks for your clarification:-) I would come up with a patch to remove this one. > >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me
