On 31.03.20 16:18, Michael S. Tsirkin wrote: > On Tue, Mar 31, 2020 at 04:09:59PM +0200, David Hildenbrand wrote: > > ... > >>>>>>>>>>>>> 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? > > .. > >> I expect the whole "steal huge pages from your guest" to be problematic, >> as I already mentioned to Alex. This needs a performance evaluation. >> >> This all smells like a lot of workload dependent fine-tuning. :) > > > So that's why I proposed the API above. > > The idea is that *if we are allocating a huge page anyway*, > rather than break it up let's send it whole to the device. > If we have smaller pages, return smaller pages. > Sorry, I still fail to see why you cannot do that with my version of balloon_pages_alloc(). But maybe I haven't understood the magic you expect to happen in alloc_page_range() :) It's just going via a different inflate queue once we have that page, as I stated in front of my draft patch "but with an optimized reporting interface". > That seems like it would always be an improvement, whatever the > workload. > Don't think so. Assume there are plenty of 4k pages lying around. It might actually be *bad* for guest performance if you take a huge page instead of all the leftover 4k pages that cannot be merged. Only at the point where you would want to break a bigger page up and report it in pieces, where it would definitely make no difference. I guess Hui Zhu now has something to look into/work on :) -- Thanks, David / dhildenb _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
