On 05/07/2019 20:35, Jason Gunthorpe wrote: > On Fri, Jul 05, 2019 at 05:24:18PM +0000, Michal Kalderon wrote: >>> From: Jason Gunthorpe <jgg@xxxxxxxx> >>> Sent: Friday, July 5, 2019 6:33 PM >>> >>> 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. >>> >> Fair enough, so as you stated above the cachabiliy can be set in the cookie. >> Would we still like to leave some bits for future ABI enhancements, requests, from user ? >> Similar to a page type that mlx has ? > > Doesn't make sense to mix and match, the page_type was just some way > to avoid tracking cookies in some cases. If we are always having a > cookie then the cookie should indicate the type based on how it was > created. Totally opaque I'm fine with removing the cachability flags from the ABI, but I don't see how the page types can be added without exposing them in the key. If we want to mmap something that's not a QP/CQ/... how can we do that? I guess only by returning some key in alloc_ucontext?
