Re: [PATCH 18/22] mm: mark DEVICE_PUBLIC as broken

Ira Weiny
2019-06-14T00:41:54Z

On Thu, Jun 13, 2019 at 07:58:29PM +0000, Jason Gunthorpe wrote:
> On Thu, Jun 13, 2019 at 12:53:02PM -0700, Ralph Campbell wrote:
> >
> > On 6/13/19 12:44 PM, Jason Gunthorpe wrote:
> > > On Thu, Jun 13, 2019 at 11:43:21AM +0200, Christoph Hellwig wrote:
> > > > The code hasn't been used since it was added to the tree, and doesn't
> > > > appear to actually be usable. Mark it as BROKEN until either a user
> > > > comes along or we finally give up on it.
> > > >
> > > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > > mm/Kconfig | 1 +
> > > > 1 file changed, 1 insertion(+)
> > > >
> > > > diff --git a/mm/Kconfig b/mm/Kconfig
> > > > index 0d2ba7e1f43e..406fa45e9ecc 100644
> > > > +++ b/mm/Kconfig
> > > > @@ -721,6 +721,7 @@ config DEVICE_PRIVATE
> > > > config DEVICE_PUBLIC
> > > > bool "Addressable device memory (like GPU memory)"
> > > > depends on ARCH_HAS_HMM
> > > > + depends on BROKEN
> > > > select HMM
> > > > select DEV_PAGEMAP_OPS
> > >
> > > This seems a bit harsh, we do have another kconfig that selects this
> > > one today:
> > >
> > > config DRM_NOUVEAU_SVM
> > > bool "(EXPERIMENTAL) Enable SVM (Shared Virtual Memory) support"
> > > depends on ARCH_HAS_HMM
> > > depends on DRM_NOUVEAU
> > > depends on STAGING
> > > select HMM_MIRROR
> > > select DEVICE_PRIVATE
> > > default n
> > > help
> > > Say Y here if you want to enable experimental support for
> > > Shared Virtual Memory (SVM).
> > >
> > > Maybe it should be depends on STAGING not broken?
> > >
> > > or maybe nouveau_svm doesn't actually need DEVICE_PRIVATE?
> > >
> > > Jason
> >
> > I think you are confusing DEVICE_PRIVATE for DEVICE_PUBLIC.
> > DRM_NOUVEAU_SVM does use DEVICE_PRIVATE but not DEVICE_PUBLIC.
>
> Indeed you are correct, never mind
>
> Hum, so the only thing this config does is short circuit here:
>
> static inline bool is_device_public_page(const struct page *page)
> {
> return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
> IS_ENABLED(CONFIG_DEVICE_PUBLIC) &&
> is_zone_device_page(page) &&
> page->pgmap->type == MEMORY_DEVICE_PUBLIC;
> }
>
> Which is called all over the place..

<sigh> yes but the earlier patch:

[PATCH 03/22] mm: remove hmm_devmem_add_resource

Removes the only place type is set to MEMORY_DEVICE_PUBLIC.

So I think it is ok. Frankly I was wondering if we should remove the public
type altogether but conceptually it seems ok. But I don't see any users of it
so... should we get rid of it in the code rather than turning the config off?

Ira

>
> So, yes, we really don't want any distro or something to turn this on
> until it has a use.
>
> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
>
> Jason
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@lists.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm