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Message-ID: <Z_0v-iFQpWlgG7oT@debian>
Date: Mon, 14 Apr 2025 09:11:20 -0700
From: Fan Ni <nifan.cxl@...il.com>
To: Ira Weiny <ira.weiny@...el.com>
Cc: Dave Jiang <dave.jiang@...el.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Dan Williams <dan.j.williams@...el.com>,
Davidlohr Bueso <dave@...olabs.net>,
Alison Schofield <alison.schofield@...el.com>,
Vishal Verma <vishal.l.verma@...el.com>, linux-cxl@...r.kernel.org,
nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org,
Li Ming <ming.li@...omail.com>
Subject: Re: [PATCH v9 00/19] DCD: Add support for Dynamic Capacity Devices
(DCD)
On Sun, Apr 13, 2025 at 05:52:08PM -0500, Ira Weiny wrote:
> A git tree of this series can be found here:
>
> https://github.com/weiny2/linux-kernel/tree/dcd-v6-2025-04-13
>
> This is now based on 6.15-rc2.
>
> Due to the stagnation of solid requirements for users of DCD I do not
> plan to rev this work in Q2 of 2025 and possibly beyond.
>
> It is anticipated that this will support at least the initial
> implementation of DCD devices, if and when they appear in the ecosystem.
> The patch set should be reviewed with the limited set of functionality in
> mind. Additional functionality can be added as devices support them.
>
> It is strongly encouraged for individuals or companies wishing to bring
> DCD devices to market review this set with the customer use cases they
> have in mind.
Hi Ira,
thanks for sending it out.
I have not got a chance to check the code or test it extensively.
I tried to test one specific case and hit issue.
I tried to add some DC extents to the extent list on the device when the
VM is launched by hacking qemu like below,
diff --git a/hw/mem/cxl_type3.c b/hw/mem/cxl_type3.c
index 87fa308495..4049fc8dd9 100644
--- a/hw/mem/cxl_type3.c
+++ b/hw/mem/cxl_type3.c
@@ -826,6 +826,11 @@ static bool cxl_create_dc_regions(CXLType3Dev *ct3d, Error **errp)
QTAILQ_INIT(&ct3d->dc.extents);
QTAILQ_INIT(&ct3d->dc.extents_pending);
+ cxl_insert_extent_to_extent_list(&ct3d->dc.extents, 0,
+ CXL_CAPACITY_MULTIPLIER, NULL, 0);
+ ct3d->dc.total_extent_count = 1;
+ ct3_set_region_block_backed(ct3d, 0, CXL_CAPACITY_MULTIPLIER);
+
return true;
}
Then after the VM is launched, I tried to create a DC region with
commmand: cxl create-region -m mem0 -d decoder0.0 -s 1G -t
dynamic_ram_a.
It works fine. As you can see below, the region is created and the
extent is showing correctly.
root@...ian:~# cxl list -r region0 -N
[
{
"region":"region0",
"resource":79725330432,
"size":1073741824,
"interleave_ways":1,
"interleave_granularity":256,
"decode_state":"commit",
"extents":[
{
"offset":0,
"length":268435456,
"uuid":"00000000-0000-0000-0000-000000000000"
}
]
}
]
However, after that, I tried to create a dax device as below, it failed.
root@...ian:~# daxctl create-device -r region0 -v
libdaxctl: __dax_regions_init: no dax regions found via: /sys/class/dax
error creating devices: No such device or address
created 0 devices
root@...ian:~#
root@...ian:~# ls /sys/class/dax
ls: cannot access '/sys/class/dax': No such file or directory
The dmesg shows the really_probe function returns early as resource
presents before probe as below,
[ 1745.505068] cxl_core:devm_cxl_add_dax_region:3251: cxl_region region0: region0: register dax_region0
[ 1745.506063] cxl_pci:__cxl_pci_mbox_send_cmd:263: cxl_pci 0000:0d:00.0: Sending command: 0x4801
[ 1745.506953] cxl_pci:cxl_pci_mbox_wait_for_doorbell:74: cxl_pci 0000:0d:00.0: Doorbell wait took 0ms
[ 1745.507911] cxl_core:__cxl_process_extent_list:1802: cxl_pci 0000:0d:00.0: Got extent list 0-0 of 1 generation Num:0
[ 1745.508958] cxl_core:__cxl_process_extent_list:1815: cxl_pci 0000:0d:00.0: Processing extent 0/1
[ 1745.509843] cxl_core:cxl_validate_extent:975: cxl_pci 0000:0d:00.0: DC extent DPA [range 0x0000000000000000-0x000000000fffffff] (DCR:[range 0x0000000000000000-0x000000007fffffff])(00000000-0000-0000-0000-000000000000)
[ 1745.511748] cxl_core:__cxl_dpa_to_region:2869: cxl decoder2.0: dpa:0x0 mapped in region:region0
[ 1745.512626] cxl_core:cxl_add_extent:460: cxl decoder2.0: Checking ED ([mem 0x00000000-0x3fffffff flags 0x80000200]) for extent [range 0x0000000000000000-0x000000000fffffff]
[ 1745.514143] cxl_core:cxl_add_extent:492: cxl decoder2.0: Add extent [range 0x0000000000000000-0x000000000fffffff] (00000000-0000-0000-0000-000000000000)
[ 1745.515485] cxl_core:online_region_extent:176: extent0.0: region extent HPA [range 0x0000000000000000-0x000000000fffffff]
[ 1745.516576] cxl_core:cxlr_notify_extent:285: cxl dax_region0: Trying notify: type 0 HPA [range 0x0000000000000000-0x000000000fffffff]
[ 1745.517768] cxl_core:cxl_bus_probe:2087: cxl_region region0: probe: 0
[ 1745.524984] cxl dax_region0: Resources present before probing
btw, I hit the same issue with the previous verson also.
Fan
>
> Series info
> ===========
>
> This series has 2 parts:
>
> Patch 1-17: Core DCD support
> Patch 18-19: 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 anticipated use cases for Dynamic Capacity is to
> allow hosts to dynamically add or remove memory from a host within a
> data center without physically changing the per-host attached memory nor
> rebooting the host.
>
> 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.
>
> An example work flow is shown below.
>
> Orchestrator FM Device Host Kernel Host User
>
> | | | | |
> |-------------- Create region ------------------------>|
> | | | | |
> | | | |<-- Create ----|
> | | | | Region |
> | | | |(dynamic_ram_a)|
> |<------------- 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
> ==============
>
> This series 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.
>
> Only a single dynamic ram partition is supported (dynamic_ram_a). The
> requirements, use cases, and existence of actual hardware devices to
> support more than one DC partition is unknown at this time. So a less
> complex implementation was chosen.
>
> 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.
>
> It is anticipated that users of the memory will carefully coordinate the
> surfacing of 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 of DAX devices 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 in this
> implementation. Future support for tags can be added when real use
> cases surface.
>
> Great care was taken to keep the extent tracking simple. Some xarray's
> needed to be added but extra software objects are kept to a minimum.
>
> Region extents are tracked as sub-devices of the DAX region. This
> ensures that region destruction cleans up all extent allocations
> properly.
>
> The major functionality of this series includes:
>
> - Getting the dynamic capacity (DC) configuration information from cxl
> devices
>
> - Configuring a DC partition found in hardware.
>
> - Enhancing the CXL and DAX regions for dynamic capacity support
> a. Maintain a logical separation between hardware extents and
> software managed extents. This provides an abstraction
> between the layers and should allow for interleaving in the
> future
>
> - Get existing hardware extent lists for endpoint decoders upon region
> creation.
>
> - Respond to DC capacity events and adjust available region memory.
> 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.)
> c. Release extents flagged with the 'more' bit individually as
> the specification allows for the asynchronous release of
> memory and the implementation is simplified by doing so.
>
> - 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) already
> accepted extent(s)
> 2) Rework DAX device interfaces, memfd has been explored a bit
> 3) Support more than 1 DC partition
>
> [1] https://github.com/weiny2/ndctl/tree/dcd-region3-2025-04-13
>
> ---
> Changes in v9:
> - djbw: pare down support to only a single DC parition
> - djbw: adjust to the new core partition processing which aligns with
> new type2 work.
> - iweiny: address smaller comments from v8
> - iweiny: rebase off of 6.15-rc1
> - Link to v8: https://patch.msgid.link/20241210-dcd-type2-upstream-v8-0-812852504400@intel.com
>
> ---
> Ira Weiny (19):
> cxl/mbox: Flag support for Dynamic Capacity Devices (DCD)
> cxl/mem: Read dynamic capacity configuration from the device
> cxl/cdat: Gather DSMAS data for DCD partitions
> cxl/core: Enforce partition order/simplify partition calls
> cxl/mem: Expose dynamic ram A partition in sysfs
> cxl/port: Add 'dynamic_ram_a' to endpoint decoder mode
> cxl/region: Add sparse DAX region support
> cxl/events: Split event msgnum configuration from irq setup
> cxl/pci: Factor out interrupt policy check
> cxl/mem: Configure dynamic capacity interrupts
> cxl/core: Return endpoint decoder information from region search
> cxl/extent: Process dynamic partition events and realize region extents
> cxl/region/extent: Expose region extent information in sysfs
> dax/bus: Factor out dev dax resize logic
> dax/region: Create resources on sparse DAX regions
> cxl/region: Read existing extents on region creation
> cxl/mem: Trace Dynamic capacity Event Record
> tools/testing/cxl: Make event logs dynamic
> tools/testing/cxl: Add DC Regions to mock mem data
>
> Documentation/ABI/testing/sysfs-bus-cxl | 100 ++-
> drivers/cxl/core/Makefile | 2 +-
> drivers/cxl/core/cdat.c | 11 +
> drivers/cxl/core/core.h | 33 +-
> drivers/cxl/core/extent.c | 495 +++++++++++++++
> drivers/cxl/core/hdm.c | 13 +-
> drivers/cxl/core/mbox.c | 632 ++++++++++++++++++-
> drivers/cxl/core/memdev.c | 87 ++-
> drivers/cxl/core/port.c | 5 +
> drivers/cxl/core/region.c | 76 ++-
> drivers/cxl/core/trace.h | 65 ++
> drivers/cxl/cxl.h | 61 +-
> drivers/cxl/cxlmem.h | 134 +++-
> drivers/cxl/mem.c | 2 +-
> drivers/cxl/pci.c | 115 +++-
> drivers/dax/bus.c | 356 +++++++++--
> drivers/dax/bus.h | 4 +-
> drivers/dax/cxl.c | 71 ++-
> drivers/dax/dax-private.h | 40 ++
> drivers/dax/hmem/hmem.c | 2 +-
> drivers/dax/pmem.c | 2 +-
> include/cxl/event.h | 31 +
> include/linux/ioport.h | 3 +
> tools/testing/cxl/Kbuild | 3 +-
> tools/testing/cxl/test/mem.c | 1021 +++++++++++++++++++++++++++----
> 25 files changed, 3102 insertions(+), 262 deletions(-)
> ---
> base-commit: 8ffd015db85fea3e15a77027fda6c02ced4d2444
> change-id: 20230604-dcd-type2-upstream-0cd15f6216fd
>
> Best regards,
> --
> Ira Weiny <ira.weiny@...el.com>
>
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