[PATCH v3 00/25] DCD: Add support for Dynamic Capacity Devices (DCD)

Ira Weiny
2024-08-16T14:44:20Z

A git tree of this series can be found here:

https://github.com/weiny2/linux-kernel/tree/dcd-v4-2024-08-16

This series requires the CXL memory notifier lock change:

https://lore.kernel.org/all/20240814-fix-notifiers-v2-1-6bab38192c7c@intel.com/

Background
==========

A Dynamic Capacity Device (DCD) (CXL 3.1 sec 9.13.3) is a CXL memory
device that allows memory capacity within a region to change
dynamically without the need for resetting the device, reconfiguring
HDM decoders, or reconfiguring software DAX regions.

One of the biggest use cases for Dynamic Capacity is to allow hosts to
share memory dynamically within a data center without increasing the
per-host attached memory.

The general flow for the addition or removal of memory is to have an
orchestrator coordinate the use of the memory. Generally there are 5
actors in such a system, the Orchestrator, Fabric Manager, the Logical
device, the Host Kernel, and a Host User.

Typical work flows are shown below.

Orchestrator FM Device Host Kernel Host User

| | | | |
|-------------- Create region ----------------------->|
| | | | |
| | | |<-- Create ---|
| | | | Region |
|<------------- Signal done --------------------------|
| | | | |
|-- Add ----->|-- Add --->|--- Add --->| |
| Capacity | Extent | Extent | |
| | | | |
| |<- Accept -|<- Accept -| |
| | Extent | Extent | |
| | | |<- Create --->|
| | | | DAX dev |-- Use memory
| | | | | |
| | | | | |
| | | |<- Release ---| <-+
| | | | DAX dev |
| | | | |
|<------------- Signal done --------------------------|
| | | | |
|-- Remove -->|- Release->|- Release ->| |
| Capacity | Extent | Extent | |
| | | | |
| |<- Release-|<- Release -| |
| | Extent | Extent | |
| | | | |
|-- Add ----->|-- Add --->|--- Add --->| |
| Capacity | Extent | Extent | |
| | | | |
| |<- Accept -|<- Accept -| |
| | Extent | Extent | |
| | | |<- Create ----|
| | | | DAX dev |-- Use memory
| | | | | |
| | | |<- Release ---| <-+
| | | | DAX dev |
|<------------- Signal done --------------------------|
| | | | |
|-- Remove -->|- Release->|- Release ->| |
| Capacity | Extent | Extent | |
| | | | |
| |<- Release-|<- Release -| |
| | Extent | Extent | |
| | | | |
|-- Add ----->|-- Add --->|--- Add --->| |
| Capacity | Extent | Extent | |
| | | |<- Create ----|
| | | | DAX dev |-- Use memory
| | | | | |
|-- Remove -->|- Release->|- Release ->| | |
| Capacity | Extent | Extent | | |
| | | | | |
| | | (Release Ignored) | |
| | | | | |
| | | |<- Release ---| <-+
| | | | DAX dev |
|<------------- Signal done --------------------------|
| | | | |
| |- Release->|- Release ->| |
| | Extent | Extent | |
| | | | |
| |<- Release-|<- Release -| |
| | Extent | Extent | |
| | | |<- Destroy ---|
| | | | Region |
| | | | |

Previous versions of this series[0] resulted in architectural comments
as well as confusion on the architecture based on the organization of
patch series itself.

This version has reordered the patches to clarify the architecture.
It also streamlines extent handling more.

The series still requires the creation of regions and DAX devices to be
synchronized with the Orchestrator and Fabric Manager. The host kernel
will reject an add extent event if the region is not created yet. It
will also ignore a release if the DAX device is created and referencing
an extent.

These synchronizations are not anticipated to be an issue with real
applications.

In order to allow for capacity to be added and removed a new concept of
a sparse DAX region is introduced. A sparse DAX region may have 0 or
more bytes of available space. The total space depends on the number
and size of the extents which have been added.

Initially it is anticipated that users of the memory will carefully
coordinate the surfacing of additional capacity with the creation of DAX
devices which use that capacity. Therefore, the allocation of the
memory to DAX devices does not allow for specific associations between
DAX device and extent. This keeps allocations very similar to existing
DAX region behavior.

Great care was taken to keep the extent tracking simple. Some xarray's
needed to be added but extra software objects were kept to a minimum.

Region extents continue to be tracked as sub-devices of the DAX region.
This ensures that region destruction cleans up all extent allocations
properly.

Due to these major changes all reviews were removed from the larger
patches. A few of the straight forward patches have kept the tags.

In summary the major functionality of this series includes:

- Getting the dynamic capacity (DC) configuration information from cxl
devices

- Configuring the DC partitions reported by hardware

- Enhancing the CXL and DAX regions for dynamic capacity support
a. Maintain a logical separation between hardware extents and
software managed region extents. This provides an
abstraction between the layers and should allow for
interleaving in the future

- Get hardware extent lists for endpoint decoders upon
region creation.

- Adjust extent/region memory available on the following events.
a. Add capacity Events
b. Release capacity events

- Host response for add capacity
a. do not accept the extent if:
If the region does not exist
or an error occurs realizing the extent
b. If the region does exist
realize a DAX region extent with 1:1 mapping (no
interleave yet)
c. Support the more bit by processing a list of extents marked
with the more bit together before setting up a response.

- Host response for remove capacity
a. If no DAX device references the extent; release the extent
b. If a reference does exist, ignore the request.
(Require FM to issue release again.)

- Modify DAX device creation/resize to account for extents within a
sparse DAX region

- Trace Dynamic Capacity events for debugging

- Add cxl-test infrastructure to allow for faster unit testing
(See new ndctl branch for cxl-dcd.sh test[1])

Fan Ni's upstream of Qemu DCD was used for testing.

Remaining work:

1) Integrate the QoS work from Dave Jiang
2) Interleave support

Possible additional work depending on requirements:

1) Allow mapping to specific extents (perhaps based on
label/tag)
2) Release extents when DAX devices are released if a release
was previously seen from the device
3) Accept a new extent which extends (but overlaps) an existing
extent(s)
4) Rework DAX device interfaces, memfd has been explored a bit

[0] v1: https://lore.kernel.org/all/20240324-dcd-type2-upstream-v1-0-b7b00d623625@intel.com/
[1] https://github.com/weiny2/ndctl/tree/dcd-region2-2024-08-15

---
Major changes:
- Jonathan: support the more bit
- djbw: Allow more than 1 region per DC partition
- All: Address the many comments on the series.
- iweiny: rebase
- iweiny: Rework the series to make it easier to review and understand
the flow
- Link to v1: https://lore.kernel.org/r/20240324-dcd-type2-upstream-v1-0-b7b00d623625@intel.com
- Link to v2: https://lore.kernel.org/all/20240816-dcd-type2-upstream-v2-0-20189a10ad7d@intel.com/

---
Ira Weiny (11):
range: Add range_overlaps()
printk: Add print format (%par) for struct range
dax: Document dax dev range tuple
cxl/pci: Delay event buffer allocation
cxl/region: Refactor common create region code
cxl/events: Split event msgnum configuration from irq setup
cxl/pci: Factor out interrupt policy check
cxl/core: Return endpoint decoder information from region search
dax/bus: Factor out dev dax resize logic
tools/testing/cxl: Make event logs dynamic
tools/testing/cxl: Add DC Regions to mock mem data

Navneet Singh (14):
cxl/mbox: Flag support for Dynamic Capacity Devices (DCD)
cxl/mem: Read dynamic capacity configuration from the device
cxl/core: Separate region mode from decoder mode
cxl/region: Add dynamic capacity decoder and region modes
cxl/hdm: Add dynamic capacity size support to endpoint decoders
cxl/port: Add endpoint decoder DC mode support to sysfs
cxl/mem: Expose DCD partition capabilities in sysfs
cxl/region: Add sparse DAX region support
cxl/mem: Configure dynamic capacity interrupts
cxl/extent: Process DCD events and realize region extents
cxl/region/extent: Expose region extent information in sysfs
dax/region: Create resources on sparse DAX regions
cxl/region: Read existing extents on region creation
cxl/mem: Trace Dynamic capacity Event Record

Documentation/ABI/testing/sysfs-bus-cxl | 68 ++-
Documentation/core-api/printk-formats.rst | 14 +
drivers/cxl/core/Makefile | 2 +-
drivers/cxl/core/core.h | 33 +-
drivers/cxl/core/extent.c | 467 ++++++++++++++
drivers/cxl/core/hdm.c | 206 ++++++-
drivers/cxl/core/mbox.c | 578 +++++++++++++++++-
drivers/cxl/core/memdev.c | 101 ++-
drivers/cxl/core/port.c | 13 +-
drivers/cxl/core/region.c | 173 ++++--
drivers/cxl/core/trace.h | 65 ++
drivers/cxl/cxl.h | 122 +++-
drivers/cxl/cxlmem.h | 128 +++-
drivers/cxl/pci.c | 123 +++-
drivers/dax/bus.c | 352 +++++++++--
drivers/dax/bus.h | 4 +-
drivers/dax/cxl.c | 73 ++-
drivers/dax/dax-private.h | 39 +-
drivers/dax/hmem/hmem.c | 2 +-
drivers/dax/pmem.c | 2 +-
fs/btrfs/ordered-data.c | 10 +-
include/linux/cxl-event.h | 32 +
include/linux/range.h | 7 +
lib/vsprintf.c | 37 ++
tools/testing/cxl/Kbuild | 3 +-
tools/testing/cxl/test/mem.c | 981 ++++++++++++++++++++++++++----
26 files changed, 3327 insertions(+), 308 deletions(-)
---
base-commit: 3cef9316df4cda21b5bf25e4230221b02050dfa1
change-id: 20230604-dcd-type2-upstream-0cd15f6216fd

Best regards,
--
Ira Weiny <ira.weiny@intel.com>