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. -- Thanks, David / dhildenb _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
