On Tue 24-10-17 13:44:23, Joonsoo Kim wrote: > On Mon, Oct 23, 2017 at 10:10:09AM +0200, Michal Hocko wrote: [...] > > My intuitive understanding of set_migratetype_isolate is that it either > > suceeds and that means that the given pfn range can be isolated for the > > given type of allocation (be it movable or cma). No new pages will be > > allocated from this range to allow converging into a free range in a > > finit amount of time. At least this is how the hotplug code would like > > to use it and I suppose that the alloc_contig_range would like to > > guarantee the same to not rely on a fixed amount of migration attempts. > > Yes, alloc_contig_range() also want to guarantee the similar thing. > Major difference between them is 'given pfn range'. memory hotplug > works by pageblock unit but alloc_contig_range() doesn't. > alloc_contig_range() works by the page unit. However, there is no easy > way to isolate individual page so it uses pageblock isolation > regardless of 'given pfn range'.
I am still confused. So when is it safe to isolate a page from the CMA pageblock for something that is not a CMA allocation request? Don't we lose a CMA guanratee that way? [...] > > That being said, I would much rather see MIGRATE_CMA case special cased > > than duplicate the already confusing API but I will not insist of > > course. > > Okay. I atteach the patch. Andrew, could you revert Michal's series > and apply this patch first? Perhaps, Michal will resend his series on > top of this one. I am not convinced about this approach but I will not argue about the patch though. If this is seen as a right way forward, I will rebase my patches on top. -- Michal Hocko SUSE Labs
