The device-dax facility allows an address range to be directly mapped
through a chardev, or turned around and hotplugged to the core kernel
page allocator as System-RAM. It is the baseline mechanism for
converting persistent memory (pmem) to be used as another volatile
memory pool i.e. the current Memory Tiering hot topic on linux-mm.
In the case of pmem the nvdimm-namespace-label mechanism can sub-divide
it, but that labeling mechanism is not available / applicable to
soft-reserved ("EFI specific purpose") memory . This series provides
a sysfs-mechanism for the daxctl utility to enable provisioning of
volatile-soft-reserved memory ranges.
The motivations for this facility are:
1/ Allow performance differentiated memory ranges to be split between
kernel-managed and directly-accessed use cases.
2/ Allow physical memory to be provisioned along performance relevant
address boundaries. For example, divide a memory-side cache  along
3/ Parcel out soft-reserved memory to VMs using device-dax as a security
/ permissions boundary . Specifically I have seen people (ab)using
memmap=nn!ss (mark System-RAM as Peristent Memory) just to get the
device-dax interface on custom address ranges.
The baseline for this series is today's next/master + "[PATCH v2 0/6]
Manual definition of Soft Reserved memory devices" .
Big thanks to Joao for the early testing and feedback on this series!
Given the dependencies on the memremap_pages() reworks in Andrew's tree
and the proximity to v5.7 this is clearly v5.8 material. The patches in
most need of a second opinion are the memremap_pages() reworks to switch
from 'struct resource' to 'struct range' and allow for an array of
ranges to be mapped at once.
Dan Williams (12):
device-dax: Drop the dax_region.pfn_flags attribute
device-dax: Move instance creation parameters to 'struct dev_dax_data'
device-dax: Make pgmap optional for instance creation
device-dax: Kill dax_kmem_res
device-dax: Add an allocation interface for device-dax instances
device-dax: Introduce seed devices
drivers/base: Make device_find_child_by_name() compatible with sysfs inputs
device-dax: Add resize support
mm/memremap_pages: Convert to 'struct range'
mm/memremap_pages: Support multiple ranges per invocation
device-dax: Add dis-contiguous resource support
device-dax: Introduce 'mapping' devices
arch/powerpc/kvm/book3s_hv_uvmem.c | 14 -
drivers/base/core.c | 2
drivers/dax/bus.c | 877 ++++++++++++++++++++++++++++++--
drivers/dax/bus.h | 28 +
drivers/dax/dax-private.h | 36 +
drivers/dax/device.c | 97 ++--
drivers/dax/hmem/hmem.c | 18 -
drivers/dax/kmem.c | 170 +++---
drivers/dax/pmem/compat.c | 2
drivers/dax/pmem/core.c | 22 +
drivers/gpu/drm/nouveau/nouveau_dmem.c | 4
drivers/nvdimm/badrange.c | 26 -
drivers/nvdimm/claim.c | 13
drivers/nvdimm/nd.h | 3
drivers/nvdimm/pfn_devs.c | 13
drivers/nvdimm/pmem.c | 27 +
drivers/nvdimm/region.c | 21 -
drivers/pci/p2pdma.c | 12
include/linux/memremap.h | 9
include/linux/range.h | 6
mm/memremap.c | 297 ++++++-----
tools/testing/nvdimm/dax-dev.c | 22 +
tools/testing/nvdimm/test/iomap.c | 2
23 files changed, 1318 insertions(+), 403 deletions(-)