On Fri, Jul 19, 2019 at 01:38:28PM -0700, John Hubbard wrote: > On 7/19/19 5:04 AM, Pavel Machek wrote: > > On Fri 2019-07-19 05:00:43, Christoph Hellwig wrote: > >> On Fri, Jul 19, 2019 at 08:48:53AM -0300, Jason Gunthorpe wrote: > >>> It is like MMU_NOTIFIERS, if something needs it, then it will select > >>> it. > >>> > >>> Maybe it should just be a hidden kconfig anyhow as there is no reason > >>> to turn it on without also turning on a using driver. > >> > >> We can't just select it due to the odd X86_64 || PPC64 dependency. > >> > >> Which also answers Pavels question: you never really need it, as we > >> can only use it for optional functionality due to that. > > > > Okay, just explain it in the help text :-).. > > > > Alternatively... you can have WANT_HMM_MIRROR option drivers select, > > and option HMM_MIRROR which is yes if WANT_HMM_MIRROR && (X86_64 || > > PPC64), no? > > > > Yes. This really should be a hidden option that just auto-enables. It's > not ideal to require people to both *find* HMM_MIRROR, *and* figure out > that they need it. (I think it's just this way due to the history of how > HMM got merged--it started off as a kind of experimental sandbox, so > it had it's own config options, to avoid bothering anything else.) > > I'll send out a new patch to just auto-select. The WANT_HMM_MIRROR > approach seems accurate, given the (X86_64 || PPC64) complication, probably > after -rc1 is ready (I don't see the ODP code using HMM yet, so that > must not have been merged yet.) > > Longer term, I vaguely recall that there is no strong reason preventing > HMM from being made to work on other arches, and am hoping that it was > just done this way to save development time. I don't want to leave it > this way unless there's a good reason to.
No one has given me a satisfactory answer about the restriction either. The only thing this kconfig controls that could possibly be arch specific is the page walking code in hmm_range_snapshot and related. Maybe there is/was some arch entanglement there? Jason
