Re: [PATCH v4 00/28] DCD: Add support for Dynamic Capacity Devices (DCD)

[Fan Ni <nifan.cxl@gmail.com>]

On Mon, Oct 07, 2024 at 06:16:06PM -0500, Ira Weiny wrote:
> A git tree of this series can be found here:
> 
> 	https://github.com/weiny2/linux-kernel/tree/dcd-v4-2024-10-04
> 
> Series info
> ===========
> 

Hi Ira,

Based on current DC extent release logic, when the extent to release is
in use (for example, created a dax device), no response (4803h) will be sent.
Should we send a response with empty extent list instead?

Fan


> This series has 5 parts:
> 
> Patch 1-3: Add %pra printk format for struct range
> Patch 4: Add core range_overlaps() function
> Patch 5-6: CXL clean up/prelim patches
> Patch 7-26: Core DCD support
> Patch 27-28: cxl_test support
> 
> 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     |
>     |             |           |            |              |
> 
> Implementation
> ==============
> 
> The series still requires the creation of regions and DAX devices to be
> closely synchronized with the Orchestrator and Fabric Manager.  The host
> kernel will reject extents if a region is not yet created.  It also
> ignores extent release if memory is in use (DAX device created).  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.
> 
> To keep the DAX memory allocation aligned with the existing DAX devices
> which do not have tags extents are not allowed to have tags.  Future
> support for tags is planned.
> 
> 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.
> 
> Some review tags were kept if a patch did not change.
> 
> 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 event 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])
> 
> - Only support 0 value extent tags
> 
> Fan Ni's upstream of Qemu DCD was used for testing.
> 
> Remaining work:
> 
> 	1) Allow mapping to specific extents (perhaps based on
> 	   label/tag)
> 	   1a) devise region size reporting based on tags
> 	2) Interleave support
> 
> Possible additional work depending on requirements:
> 
> 	1) Accept a new extent which extends (but overlaps) an existing
> 	   extent(s)
> 	2) Release extents when DAX devices are released if a release
> 	   was previously seen from the device
> 	3) Rework DAX device interfaces, memfd has been explored a bit
> 
> [1] https://github.com/weiny2/ndctl/tree/dcd-region2-2024-10-01
> 
> ---
> Major changes in v4:
> - iweiny: rebase to 6.12-rc
> - iweiny: Add qos data to regions
> - Jonathan: Fix up shared region detection
> - Jonathan/jgroves/djbw/iweiny: Ignore 0 value tags
> - iweiny: Change DCD partition sysfs entries to allow for qos class and
>   additional parameters per partition
> - Petr/Andy: s/%par/%pra/
> - Andy: Share logic between printing struct resource and struct range
> - Link to v3: https://patch.msgid.link/20240816-dcd-type2-upstream-v3-0-7c9b96cba6d7@intel.com
> 
> ---
> Ira Weiny (14):
>       test printk: Add very basic struct resource tests
>       printk: Add print format (%pra) for struct range
>       cxl/cdat: Use %pra for dpa range outputs
>       range: Add range_overlaps()
>       dax: Document dax dev range tuple
>       cxl/pci: Delay event buffer allocation
>       cxl/cdat: Gather DSMAS data for DCD regions
>       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/mem: Expose DCD partition capabilities in sysfs
>       cxl/port: Add endpoint decoder DC mode support to 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   | 120 +++-
>  Documentation/core-api/printk-formats.rst |  13 +
>  drivers/cxl/core/Makefile                 |   2 +-
>  drivers/cxl/core/cdat.c                   |  52 +-
>  drivers/cxl/core/core.h                   |  33 +-
>  drivers/cxl/core/extent.c                 | 486 +++++++++++++++
>  drivers/cxl/core/hdm.c                    | 213 ++++++-
>  drivers/cxl/core/mbox.c                   | 605 ++++++++++++++++++-
>  drivers/cxl/core/memdev.c                 | 130 +++-
>  drivers/cxl/core/port.c                   |  13 +-
>  drivers/cxl/core/region.c                 | 170 ++++--
>  drivers/cxl/core/trace.h                  |  65 ++
>  drivers/cxl/cxl.h                         | 122 +++-
>  drivers/cxl/cxlmem.h                      | 131 +++-
>  drivers/cxl/pci.c                         | 123 +++-
>  drivers/dax/bus.c                         | 352 +++++++++--
>  drivers/dax/bus.h                         |   4 +-
>  drivers/dax/cxl.c                         |  72 ++-
>  drivers/dax/dax-private.h                 |  47 +-
>  drivers/dax/hmem/hmem.c                   |   2 +-
>  drivers/dax/pmem.c                        |   2 +-
>  fs/btrfs/ordered-data.c                   |  10 +-
>  include/acpi/actbl1.h                     |   2 +
>  include/cxl/event.h                       |  32 +
>  include/linux/range.h                     |   7 +
>  lib/test_printf.c                         |  70 +++
>  lib/vsprintf.c                            |  55 +-
>  tools/testing/cxl/Kbuild                  |   3 +-
>  tools/testing/cxl/test/mem.c              | 960 ++++++++++++++++++++++++++----
>  29 files changed, 3576 insertions(+), 320 deletions(-)
> ---
> base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc
> change-id: 20230604-dcd-type2-upstream-0cd15f6216fd
> 
> Best regards,
> -- 
> Ira Weiny <ira.weiny@intel.com>
> 

-- 
Fan Ni