On Thu, Mar 12, 2020 at 09:51:25AM +0100, David Hildenbrand wrote: > On 12.03.20 09:47, Michael S. Tsirkin wrote: > > On Thu, Mar 12, 2020 at 09:37:32AM +0100, David Hildenbrand wrote: > >> 2. You are essentially stealing THPs in the guest. So the fastest > >> mapping (THP in guest and host) is gone. The guest won't be able to make > >> use of THP where it previously was able to. I can imagine this implies a > >> performance degradation for some workloads. This needs a proper > >> performance evaluation. > > > > I think the problem is more with the alloc_pages API. > > That gives you exactly the given order, and if there's > > a larger chunk available, it will split it up. > > > > But for balloon - I suspect lots of other users, > > we do not want to stress the system but if a large > > chunk is available anyway, then we could handle > > that more optimally by getting it all in one go. > > > > > > So if we want to address this, IMHO this calls for a new API. > > Along the lines of > > > > struct page *alloc_page_range(gfp_t gfp, unsigned int min_order, > > unsigned int max_order, unsigned int *order) > > > > the idea would then be to return at a number of pages in the given > > range. > > > > What do you think? Want to try implementing that? > > You can just start with the highest order and decrement the order until > your allocation succeeds using alloc_pages(), which would be enough for > a first version. At least I don't see the immediate need for a new > kernel API. Well there's still a chance of splitting a big page if one becomes available meanwhile. But OK. > -- > Thanks, > > David / dhildenb _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
