linux/Documentation/ABI/testing/sysfs-bus-dax
Vishal Verma 73954d379e dax: add a sysfs knob to control memmap_on_memory behavior
Add a sysfs knob for dax devices to control the memmap_on_memory setting
if the dax device were to be hotplugged as system memory.

The default memmap_on_memory setting for dax devices originating via pmem
or hmem is set to 'false' - i.e.  no memmap_on_memory semantics, to
preserve legacy behavior.  For dax devices via CXL, the default is on. 
The sysfs control allows the administrator to override the above defaults
if needed.

Link: https://lkml.kernel.org/r/20240124-vv-dax_abi-v7-5-20d16cb8d23d@intel.com
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Tested-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Huang, Ying <ying.huang@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-22 10:24:40 -08:00

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What: /sys/bus/dax/devices/daxX.Y/align
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(RW) Provides a way to specify an alignment for a dax device.
Values allowed are constrained by the physical address ranges
that back the dax device, and also by arch requirements.
What: /sys/bus/dax/devices/daxX.Y/mapping
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(WO) Provides a way to allocate a mapping range under a dax
device. Specified in the format <start>-<end>.
What: /sys/bus/dax/devices/daxX.Y/mapping[0..N]/start
What: /sys/bus/dax/devices/daxX.Y/mapping[0..N]/end
What: /sys/bus/dax/devices/daxX.Y/mapping[0..N]/page_offset
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(RO) A dax device may have multiple constituent discontiguous
address ranges. These are represented by the different
'mappingX' subdirectories. The 'start' attribute indicates the
start physical address for the given range. The 'end' attribute
indicates the end physical address for the given range. The
'page_offset' attribute indicates the offset of the current
range in the dax device.
What: /sys/bus/dax/devices/daxX.Y/resource
Date: June, 2019
KernelVersion: v5.3
Contact: nvdimm@lists.linux.dev
Description:
(RO) The resource attribute indicates the starting physical
address of a dax device. In case of a device with multiple
constituent ranges, it indicates the starting address of the
first range.
What: /sys/bus/dax/devices/daxX.Y/size
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(RW) The size attribute indicates the total size of a dax
device. For creating subdivided dax devices, or for resizing
an existing device, the new size can be written to this as
part of the reconfiguration process.
What: /sys/bus/dax/devices/daxX.Y/numa_node
Date: November, 2019
KernelVersion: v5.5
Contact: nvdimm@lists.linux.dev
Description:
(RO) If NUMA is enabled and the platform has affinitized the
backing device for this dax device, emit the CPU node
affinity for this device.
What: /sys/bus/dax/devices/daxX.Y/target_node
Date: February, 2019
KernelVersion: v5.1
Contact: nvdimm@lists.linux.dev
Description:
(RO) The target-node attribute is the Linux numa-node that a
device-dax instance may create when it is online. Prior to
being online the device's 'numa_node' property reflects the
closest online cpu node which is the typical expectation of a
device 'numa_node'. Once it is online it becomes its own
distinct numa node.
What: $(readlink -f /sys/bus/dax/devices/daxX.Y)/../dax_region/available_size
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(RO) The available_size attribute tracks available dax region
capacity. This only applies to volatile hmem devices, not pmem
devices, since pmem devices are defined by nvdimm namespace
boundaries.
What: $(readlink -f /sys/bus/dax/devices/daxX.Y)/../dax_region/size
Date: July, 2017
KernelVersion: v5.1
Contact: nvdimm@lists.linux.dev
Description:
(RO) The size attribute indicates the size of a given dax region
in bytes.
What: $(readlink -f /sys/bus/dax/devices/daxX.Y)/../dax_region/align
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(RO) The align attribute indicates alignment of the dax region.
Changes on align may not always be valid, when say certain
mappings were created with 2M and then we switch to 1G. This
validates all ranges against the new value being attempted, post
resizing.
What: $(readlink -f /sys/bus/dax/devices/daxX.Y)/../dax_region/seed
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(RO) The seed device is a concept for dynamic dax regions to be
able to split the region amongst multiple sub-instances. The
seed device, similar to libnvdimm seed devices, is a device
that starts with zero capacity allocated and unbound to a
driver.
What: $(readlink -f /sys/bus/dax/devices/daxX.Y)/../dax_region/create
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(RW) The create interface to the dax region provides a way to
create a new unconfigured dax device under the given region, which
can then be configured (with a size etc.) and then probed.
What: $(readlink -f /sys/bus/dax/devices/daxX.Y)/../dax_region/delete
Date: October, 2020
KernelVersion: v5.10
Contact: nvdimm@lists.linux.dev
Description:
(WO) The delete interface for a dax region provides for deletion
of any 0-sized and idle dax devices.
What: $(readlink -f /sys/bus/dax/devices/daxX.Y)/../dax_region/id
Date: July, 2017
KernelVersion: v5.1
Contact: nvdimm@lists.linux.dev
Description:
(RO) The id attribute indicates the region id of a dax region.
What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
Date: January, 2024
KernelVersion: v6.8
Contact: nvdimm@lists.linux.dev
Description:
(RW) Control the memmap_on_memory setting if the dax device
were to be hotplugged as system memory. This determines whether
the 'altmap' for the hotplugged memory will be placed on the
device being hotplugged (memmap_on_memory=1) or if it will be
placed on regular memory (memmap_on_memory=0). This attribute
must be set before the device is handed over to the 'kmem'
driver (i.e. hotplugged into system-ram). Additionally, this
depends on CONFIG_MHP_MEMMAP_ON_MEMORY, and a globally enabled
memmap_on_memory parameter for memory_hotplug. This is
typically set on the kernel command line -
memory_hotplug.memmap_on_memory set to 'true' or 'force'."