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Message-ID: <aEcVX-DEHJrMnAi-@lg> Date: Mon, 9 Jun 2025 10:09:51 -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 Tue, Jun 03, 2025 at 09:32:18AM -0700, Fan Ni wrote: > 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, > I have a general question about DCD. > > How will the start dpa of the first region be set before any extent is > offer to the hosts? > > In this series, no dpa gap (skip) is allowed between static capacity and > dynamic capacity. That seems to imply some component that knows the layout > of the host memory will need to set the start dpa of the first dc region? > The firmware? > > Also, if a DC extent is shared among multiple hosts each of which has > different memory configuration, how the dcd device provides the extents > to each host to make sure there is no dpa gap between static and dynamic > capacity range on all the hosts? > It seems the start dpa of dcd needs to be different for each host. No sure how > to achieve that. > > Fan Ignore the above message, the question does not make sense. 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> > > > > -- > Fan Ni -- Fan Ni
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