On Fri, Apr 07, 2017 at 11:37:34AM +1000, Balbir Singh wrote: > On Wed, 2017-04-05 at 16:40 -0400, Jérôme Glisse wrote: > > This introduce a simple struct and associated helpers for device driver > > to use when hotpluging un-addressable device memory as ZONE_DEVICE. It > > will find a unuse physical address range and trigger memory hotplug for > > it which allocates and initialize struct page for the device memory. > > > > Signed-off-by: Jérôme Glisse <jgli...@redhat.com> > > Signed-off-by: Evgeny Baskakov <ebaska...@nvidia.com> > > Signed-off-by: John Hubbard <jhubb...@nvidia.com> > > Signed-off-by: Mark Hairgrove <mhairgr...@nvidia.com> > > Signed-off-by: Sherry Cheung <sche...@nvidia.com> > > Signed-off-by: Subhash Gutti <sgu...@nvidia.com> > > --- > > include/linux/hmm.h | 114 +++++++++++++++ > > mm/Kconfig | 9 ++ > > mm/hmm.c | 398 > > ++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 521 insertions(+) > > > > +/* > > + * To add (hotplug) device memory, HMM assumes that there is no real > > resource > > + * that reserves a range in the physical address space (this is intended > > to be > > + * use by unaddressable device memory). It will reserve a physical range > > big > > + * enough and allocate struct page for it. > > I've found that the implementation of this is quite non-portable, in that > starting from iomem_resource.end+1-size (which is effectively -size) on > my platform (powerpc) does not give expected results. It could be that > additional changes are needed to arch_add_memory() to support this > use case.
The CDM version does not use that part, that being said isn't -size a valid value we care only about unsigned here ? What is the end value on powerpc ? In any case this sounds more like a unsigned/signed arithmetic issue, i will look into it. > > > + > > + size = ALIGN(size, SECTION_SIZE); > > + addr = (iomem_resource.end + 1ULL) - size; > > > Why don't we allocate_resource() with the right constraints and get a new > unused region? The issue with allocate_resource() is that it does scan the resource tree from lower address to higher ones. I was told that it was less likely to have hotplug issue conflict if i pick highest physicall address for the device memory hence why i do my own scan from the end toward the start. Again all this function does not apply to PPC, it can be hidden behind x86 config if you prefer it. Cheers, Jérôme
