Dan Williams <[email protected]> writes: > The "sub-section memory hotplug" facility allows memremap_pages() users > like libnvdimm to compensate for hardware platforms like x86 that have a > section size larger than their hardware memory mapping granularity. The > compensation that sub-section support affords is being tolerant of > physical memory resources shifting by units smaller (64MiB on x86) than > the memory-hotplug section size (128 MiB). Where the platform > physical-memory mapping granularity is limited by the number and > capability of address-decode-registers in the memory controller. > > While the sub-section support allows memremap_pages() to operate on > sub-section (2MiB) granularity, the Power architecture may still > require 16MiB alignment on "!radix_enabled()" platforms. > > In order for libnvdimm to be able to detect and manage this per-arch > limitation, introduce memremap_compat_align() as a common minimum > alignment across all driver-facing memory-mapping interfaces, and let > Power override it to 16MiB in the "!radix_enabled()" case. > > The assumption / requirement for 16MiB to be a viable > memremap_compat_align() value is that Power does not have platforms > where its equivalent of address-decode-registers never hardware remaps a > persistent memory resource on smaller than 16MiB boundaries. Note that I > tried my best to not add a new Kconfig symbol, but header include > entanglements defeated the #ifndef memremap_compat_align design pattern > and the need to export it defeats the __weak design pattern for arch > overrides. > > Based on an initial patch by Aneesh. > Reviewed-by: Aneesh Kumar K.V <[email protected]>
> Link: > http://lore.kernel.org/r/capcyv4gbgnp95apyabcsocea50tqj9b5h__83vgngjq3oug...@mail.gmail.com > Reported-by: Aneesh Kumar K.V <[email protected]> > Reported-by: Jeff Moyer <[email protected]> > Cc: Benjamin Herrenschmidt <[email protected]> > Cc: Paul Mackerras <[email protected]> > Signed-off-by: Dan Williams <[email protected]> > --- > arch/powerpc/Kconfig | 1 + > arch/powerpc/mm/ioremap.c | 21 +++++++++++++++++++++ > drivers/nvdimm/pfn_devs.c | 2 +- > include/linux/memremap.h | 8 ++++++++ > include/linux/mmzone.h | 1 + > lib/Kconfig | 3 +++ > mm/memremap.c | 23 +++++++++++++++++++++++ > 7 files changed, 58 insertions(+), 1 deletion(-) >
