On 05/13/2016 04:12 AM, Neo Jia wrote: > On Thu, May 12, 2016 at 01:05:52PM -0600, Alex Williamson wrote: >> >> If you're trying to equate the scale of what we need to track vs what >> type1 currently tracks, they're significantly different. Possible >> things we need to track include the pfn, the iova, and possibly a >> reference count or some sort of pinned page map. In the pin-all model >> we can assume that every page is pinned on map and unpinned on unmap, >> so a reference count or map is unnecessary. We can also assume that we >> can always regenerate the pfn with get_user_pages() from the vaddr, so >> we don't need to track that. > > Hi Alex, > > Thanks for pointing this out, we will not track those in our next rev and > get_user_pages will be used from the vaddr as you suggested to handle the > single VM with both passthru + mediated device case. >
Just a gut feeling: Calling GUP every time for a particular vaddr, means locking mm->mmap_sem every time for a particular process. If the VM has dozens of VCPU, which is not rare, the semaphore is likely to be the bottleneck. -- Thanks, Jike
