On Fri, Dec 04, 2020 at 01:36:27PM -0800, John Hubbard wrote: > On 12/4/20 11:39 AM, Jason Gunthorpe wrote: > > Long ago there wasn't a FOLL_LONGTERM flag so this DAX check was done by > > post-processing the VMA list. > > > > These days it is trivial to just check each VMA to see if it is DAX before > > processing it inside __get_user_pages() and return failure if a DAX VMA is > > encountered with FOLL_LONGTERM. > > > > Removing the allocation of the VMA list is a significant speed up for many > > call sites. > > This all looks nice, and if you actually have quantifiable perf results as you > imply above, then let's put them right here. I don't really have a good perf setup, it is just obvious that removing the calls to the allocator will speed up cases like RDMA that call gup in batches of 512 pages, or vfio which calls in batches of 1. :) Jason
