ndctl-enable-namespace - enable the given namespace(s)
ndctl enable-namespace <namespace> [<options>]
THEORY OF OPERATION¶
The capacity of an NVDIMM REGION (contiguous span of persistent
memory) is accessed via one or more NAMESPACE devices. REGION is the Linux
term for what ACPI and UEFI call a DIMM-interleave-set, or a
system-physical-address-range that is striped (by the memory controller)
across one or more memory modules.
The UEFI specification defines the NVDIMM Label Protocol as
the combination of label area access methods and a data format for
provisioning one or more NAMESPACE objects from a REGION. Note that label
support is optional and if Linux does not detect the label capability it
will automatically instantiate a "label-less" namespace per
region. Examples of label-less namespaces are the ones created by the
kernel’s memmap=ss!nn command line option (see the nvdimm wiki
on kernel.org), or NVDIMMs without a valid namespace index in their
Label-less namespaces lack many of the features of their
cousins. For example, their size cannot be modified, or they cannot be fully
destroyed (i.e. the space reclaimed). A destroy operation will zero
any mode-specific metadata. Finally, for create-namespace operations on
label-less namespaces, ndctl bypasses the region capacity availability
checks, and always satisfies the request using the full region capacity. The
only reconfiguration operation supported on a label-less namespace is
changing its mode.
A namespace can be provisioned to operate in one of 4 modes,
fsdax, devdax, sector, and raw. Here are the
expected usage models for these modes:
•fsdax: Filesystem-DAX mode is the default mode of
a namespace when specifying ndctl create-namespace
with no options. It
creates a block device (/dev/pmemX[.Y]) that supports the DAX capabilities of
Linux filesystems (xfs and ext4 to date). DAX removes the page cache from the
I/O path and allows mmap(2)
to establish direct mappings to persistent memory
media. The DAX capability enables workloads / working-sets that would exceed
the capacity of the page cache to scale up to the capacity of persistent
memory. Workloads that fit in page cache or perform bulk data transfers may
not see benefit from DAX. When in doubt, pick this mode.
•devdax: Device-DAX mode enables similar mmap(2)
DAX mapping capabilities as Filesystem-DAX. However, instead of a block-device
that can support a DAX-enabled filesystem, this mode emits a single character
device file (/dev/daxX.Y). Use this mode to assign persistent memory to a
virtual-machine, register persistent memory for RDMA, or when gigantic
mappings are needed.
•sector: Use this mode to host legacy filesystems
that do not checksum metadata or applications that are not prepared for torn
sectors after a crash. Expected usage for this mode is for small boot volumes.
This mode is compatible with other operating systems.
•raw: Raw mode is effectively just a memory disk
that does not support DAX. Typically this indicates a namespace that was
created by tooling or another operating system that did not know how to create
a Linux fsdax or devdax mode namespace. This mode is compatible
with other operating systems, but again, does not support DAX operation.
A namespaceX.Y device name. The keyword all
can be specified to carry out the operation on every namespace in the system,
optionally filtered by region (see --region=option)
A regionX device name, or a region id number.
Restrict the operation to the specified region(s). The keyword all can
be specified to indicate the lack of any restriction, however this is the same
as not supplying a --region option at all.
A bus id number, or a provider string (e.g.
"ACPI.NFIT"). Restrict the operation to the specified bus(es). The
keyword all can be specified to indicate the lack of any restriction,
however this is the same as not supplying a --bus option at all.
Emit debug messages for the namespace operation
Copyright © 2016 - 2020, Intel Corporation. License GPLv2:
GNU GPL version 2 <http://gnu.org/licenses/gpl.html>. This is
free software: you are free to change and redistribute it. There is NO
WARRANTY, to the extent permitted by law.