On Fri, Jul 05, 2019 at 03:29:03PM +0000, Michal Kalderon wrote: > > From: Jason Gunthorpe <jgg@xxxxxxxx> > > Sent: Thursday, July 4, 2019 3:35 PM > > > > External Email > > > > On Wed, Jul 03, 2019 at 11:19:34AM +0300, Gal Pressman wrote: > > > On 03/07/2019 1:31, Jason Gunthorpe wrote: > > > >> Seems except Mellanox + hns the mmap flags aren't ABI. > > > >> Also, current Mellanox code seems like it won't benefit from mmap > > > >> cookie helper functions in any case as the mmap function is very > > > >> specific and the flags used indicate the address and not just how to map > > it. > > > > > > > > IMHO, mlx5 has a goofy implementaiton here as it codes all of the > > > > object type, handle and cachability flags in one thing. > > > > > > Do we need object type flags as well in the generic mmap code? > > > > At the end of the day the driver needs to know what page to map during the > > mmap syscall. > > > > mlx5 does this by encoding the page type in the address, and then many > > types have seperate lookups based onthe offset for the actual page. > > > > IMHO the single lookup and opaque offset is generally better.. > > > > Since the mlx5 scheme is ABI it can't be changed unfortunately. > > > > If you want to do user controlled cachability flags, or not, is a fair question, > > but they still become ABI.. > > > > I'm wondering if it really makes sense to do that during the mmap, or if the > > cachability should be set as part of creating the cookie? > > > > > Another issue is that these flags aren't exposed in an ABI file, so a > > > userspace library can't really make use of it in current state. > > > > Woops. > > > > Ah, this is all ABI so you need to dig out of this hole ASAP :) > > > Jason, I didn't follow - what is all ABI? > currently EFA implementation encodes the cachability inside the key, > It's not exposed in ABI file and is opaque to user-space. The kernel decides on the cachability > And get's it back in the key when mmap is called. It seems good > enough for the current cases. Then the key 'offset' should not include cachability information at all. Jason
