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Date: Mon, 25 Mar 2024 12:24:02 -0700 From: fan <nifan.cxl@...il.com> To: ira.weiny@...el.com Cc: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>, Navneet Singh <navneet.singh@...el.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-btrfs@...r.kernel.org, linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org, Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com> Subject: Re: [PATCH 00/26] DCD: Add support for Dynamic Capacity Devices (DCD) On Sun, Mar 24, 2024 at 04:18:03PM -0700, ira.weiny@...el.com wrote: > A git tree of this series can be found here: > > https://github.com/weiny2/linux-kernel/tree/dcd-2024-03-24 > > Pre-requisite: > ============== > > The locking introduced by Vishal for DAX regions: > https://lore.kernel.org/all/20240124-vv-dax_abi-v7-1-20d16cb8d23d@intel.com/T/#u > > Background > ========== > > A Dynamic Capacity Device (DCD) (CXL 3.1 sec 9.13.3) is a CXL memory > device that allows the memory capacity 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 Device > the host sees, 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 RFCs of this series[0] resulted in significant architectural > comments. Previous versions allowed memory capacity to be accepted by > the host regardless of the existence of a software region being mapped. > > With this new patch set the order of the create region and DAX device > creation must be synchronized with the Orchestrator adding/removing > capacity. 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. > > Neither of these synchronizations are 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 greatly simplify extent tracking. Specifically, > in comparison to previous versions of the patch set, all extent tracking > xarrays have been eliminated from the code. In addition, most of the > extra software objects and associated referenced counts have been > eliminated. > > In this version, extents are tracked purely as sub-devices of the > region. This ensures that the region destruction cleans up all extent > allocations properly. Device managed callbacks are wired to ensure any > additional data required for DAX device references are handled > correctly. > > Due to these major changes I'm setting this new series to V1. > > In summary the major functionality of this series includes: > > - Getting the dynamic capacity (DC) configuration information from cxl > devices > > - Configuring the DC regions 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) > > - Host response for remove capacity > a. If no DAX devices reference 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 latest v5 of Qemu DCD was used for testing.[2] > > 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) > > [0] RFC v2: https://lore.kernel.org/r/20230604-dcd-type2-upstream-v2-0-f740c47e7916@intel.com > [1] https://github.com/weiny2/ndctl/tree/dcd-region2-2024-03-22 > [2] https://lore.kernel.org/all/20240304194331.1586191-1-nifan.cxl@gmail.com/ > > --- > Changes for v1: > - iweiny: Largely new series > - iweiny: Remove review tags due to the series being a major rework > - iweiny: Fix authorship for Navneet patches > - iweiny: Remove extent xarrays > - iweiny: Remove kreferences, replace with 1 use count protected under dax_rwsem > - iweiny: Mark all sysfs entries for the 6.10 June 2024 kernel > - iweiny: Remove gotos > - iweiny: Fix 0day issues > - Jonathan Cameron: address comments > - Navneet Singh: address comments > - Dan Williams: address comments > - Dave Jiang: address comments > - Fan Ni: address comments > - Jørgen Hansen: address comments > - Link to RFC v2: https://lore.kernel.org/r/20230604-dcd-type2-upstream-v2-0-f740c47e7916@intel.com > Hi Ira, Have not got a chance to check the code yet, but I noticed one thing when testing with my DCD emulation code. Currently, if we do partial release, it seems the whole extent will be removed. Is it designed intentionally? Fan > --- > Ira Weiny (12): > cxl/core: Simplify cxl_dpa_set_mode() > cxl/events: Factor out event msgnum configuration > cxl/pci: Delay event buffer allocation > cxl/pci: Factor out interrupt policy check > range: Add range_overlaps() > dax/bus: Factor out dev dax resize logic > dax: Document dax dev range tuple > dax/region: Prevent range mapping allocation on sparse regions > dax/region: Support DAX device creation on sparse DAX regions > tools/testing/cxl: Make event logs dynamic > tools/testing/cxl: Add DC Regions to mock mem data > tools/testing/cxl: Add Dynamic Capacity events > > Navneet Singh (14): > cxl/mbox: Flag support for Dynamic Capacity Devices (DCD) > cxl/core: Separate region mode from decoder mode > cxl/mem: Read dynamic capacity configuration from the device > cxl/region: Add dynamic capacity decoder and region modes > cxl/port: Add Dynamic Capacity mode support to endpoint decoders > cxl/port: Add dynamic capacity size support to endpoint decoders > cxl/mem: Expose device dynamic capacity capabilities > cxl/region: Add Dynamic Capacity CXL region support > cxl/mem: Configure dynamic capacity interrupts > cxl/region: Read existing extents on region creation > cxl/extent: Realize extent devices > dax/region: Create extent resources on DAX region driver load > cxl/mem: Handle DCD add & release capacity events. > cxl/mem: Trace Dynamic capacity Event Record > > Documentation/ABI/testing/sysfs-bus-cxl | 60 ++- > drivers/cxl/core/Makefile | 1 + > drivers/cxl/core/core.h | 10 + > drivers/cxl/core/extent.c | 145 +++++ > drivers/cxl/core/hdm.c | 254 +++++++-- > drivers/cxl/core/mbox.c | 591 ++++++++++++++++++++- > drivers/cxl/core/memdev.c | 76 +++ > drivers/cxl/core/port.c | 19 + > drivers/cxl/core/region.c | 334 +++++++++++- > drivers/cxl/core/trace.h | 65 +++ > drivers/cxl/cxl.h | 127 ++++- > drivers/cxl/cxlmem.h | 114 ++++ > drivers/cxl/mem.c | 45 ++ > drivers/cxl/pci.c | 122 +++-- > drivers/dax/bus.c | 353 +++++++++--- > drivers/dax/bus.h | 4 +- > drivers/dax/cxl.c | 127 ++++- > drivers/dax/dax-private.h | 40 +- > drivers/dax/hmem/hmem.c | 2 +- > drivers/dax/pmem.c | 2 +- > fs/btrfs/ordered-data.c | 10 +- > include/linux/cxl-event.h | 31 ++ > include/linux/range.h | 7 + > tools/testing/cxl/Kbuild | 1 + > tools/testing/cxl/test/mem.c | 914 ++++++++++++++++++++++++++++---- > 25 files changed, 3152 insertions(+), 302 deletions(-) > --- > base-commit: dff54316795991e88a453a095a9322718a34034a > change-id: 20230604-dcd-type2-upstream-0cd15f6216fd > > Best regards, > -- > Ira Weiny <ira.weiny@...el.com> >
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