Re: [PATCH v5 0/9] drm/xe/madvise: Add support for purgeable buffer objects

[Matthew Brost <matthew.brost@intel.com>]

On Wed, Feb 11, 2026 at 08:56:29PM +0530, Arvind Yadav wrote:

I have a feeling from the KMD POV we are getting close for this being
ready to merge. What is the status a UMD PR to use this feature (?) as
this is a prerequisite to merging.

Also it likely time to start collecting ack's from the UMD teams on the
the uAPI patch too.

Matt 

> This patch series introduces comprehensive support for purgeable buffer objects
> in the Xe driver, enabling userspace to provide memory usage hints for better
> memory management under system pressure.
> 
> Overview:
> 
> Purgeable memory allows applications to mark buffer objects as "not currently
> needed" (DONTNEED), making them eligible for kernel reclamation during memory
> pressure. This helps prevent OOM conditions and enables more efficient GPU
> memory utilization for workloads with temporary or regeneratable data (caches,
> intermediate results, decoded frames, etc.).
> 
> Purgeable BO Lifecycle:
> 1. WILLNEED (default): BO actively needed, kernel preserves backing store
> 2. DONTNEED (user hint): BO contents discardable, eligible for purging
> 3. PURGED (kernel action): Backing store reclaimed during memory pressure
> 
> Key Design Principles:
>   - i915 compatibility: "Once purged, always purged" semantics - purged BOs
>     remain permanently invalid and must be destroyed/recreated
>   - Per-VMA state tracking: Each VMA tracks its own purgeable state, BO is
>     only marked DONTNEED when ALL VMAs across ALL VMs agree (Thomas Hellström)
>   - Safety first: Imported/exported dma-bufs blocked from purgeable state -
>     no visibility into external device usage (Matt Roper)
>   - Multiple protection layers: Validation in madvise, VM bind, mmap, and
>     fault handlers
>   - Async TLB invalidation: Uses xe_bo_trigger_rebind() for non-blocking
>     GPU mapping invalidation
>   - Scratch PTE support: Fault-mode VMs use scratch pages for safe zero reads
>     on purged BO access.
>   - Purgeable state is not applied to imported/exported dma-bufs,
>     those BOs always behave as WILLNEED.
>   - TTM shrinker integration: Encapsulated helpers manage xe_ttm_tt->purgeable
>     flag and shrinker page accounting (shrinkable vs purgeable buckets)
> 
> v2 Changes:
>   - Reordered patches: Moved shared BO helper before main implementation for
>     proper dependency order
>   - Fixed reference counting in mmap offset validation (use drm_gem_object_put)
>   - Removed incorrect claims about madvise(WILLNEED) restoring purged BOs
>   - Fixed error code documentation inconsistencies
>   - Initialize purge_state_val fields to prevent kernel memory leaks
>   - Use xe_bo_trigger_rebind() for async TLB invalidation (Thomas Hellström)
>   - Add NULL rebind with scratch PTEs for fault mode (Thomas Hellström)
>   - Implement i915-compatible retained field logic (Thomas Hellström)
>   - Skip BO validation for purged BOs in page fault handler (crash fix)
>   - Add scratch VM check in page fault path (non-scratch VMs fail fault)
> 
> v3 Changes (addressing Matt and Thomas Hellström feedback):
>   - Per-VMA purgeable state tracking: Added xe_vma->purgeable_state field
>   - Complete VMA check: xe_bo_all_vmas_dontneed() walks all VMAs across all
>     VMs to ensure unanimous DONTNEED before marking BO purgeable
>   - VMA unbind recheck: Added xe_bo_recheck_purgeable_on_vma_unbind() to
>     re-evaluate BO state when VMAs are destroyed
>   - Block external dma-bufs: Added xe_bo_is_external_dmabuf() check using
>     drm_gem_is_imported() and obj->dma_buf to prevent purging imported/exported BOs
>   - Consistent lockdep enforcement: Added xe_bo_assert_held() to all helpers
>     that access madv_purgeable state
>   - Simplified page table logic: Renamed is_null to is_null_or_purged in
>     xe_pt_stage_bind_entry() - purged BOs treated identically to null VMAs
>   - Removed unnecessary checks: Dropped redundant "&& bo" check in xe_ttm_bo_purge()
>   - Xe-specific warnings: Changed drm_warn() to XE_WARN_ON() in purge path
>   - Moved purge checks under locks: Purge state validation now done after
>     acquiring dma-resv lock in vma_lock_and_validate() and xe_pagefault_begin()
>   - Race-free fault handling: Removed unlocked purge check from
>     xe_pagefault_handle_vma(), moved to locked xe_pagefault_begin()
>   - Shrinker helper functions: Added xe_bo_set_purgeable_shrinker() and
>     xe_bo_clear_purgeable_shrinker() to encapsulate TTM purgeable flag updates
>     and shrinker page accounting, improving code clarity and maintainability
> 
> v4 Changes (addressing Matt and Thomas Hellström feedback):
>   - UAPI: Removed '__u64 reserved' field from purge_state_val union to fit
>     16-byte size constraint (Matt)
>   - Changed madv_purgeable from atomic_t to u32 across all patches (Matt)
>   - CPU fault handling: Added purged check to fastpath (xe_bo_cpu_fault_fastpath)
>     to prevent hang when accessing existing mmap of purged BO
> 
> v5 Changes (addressing Matt and Thomas Hellström feedback):
>   - Add locking documentation to madv_purgeable field comment (Matt)
>   - Introduce xe_bo_set_purgeable_state() helper (void return) to centralize
>     madv_purgeable updates with xe_bo_assert_held() and state transition
>     validation using explicit enum checks (no transition out of PURGED) (Matt)
>   - Make xe_ttm_bo_purge() return int and propagate failures from
>     xe_bo_move(); handle xe_bo_trigger_rebind() failures (e.g. no_wait_gpu
>     paths) rather than silently ignoring (Matt)
>   - Replace drm_WARN_ON with xe_assert for better Xe-specific assertions (Matt)
>   - Hook purgeable handling into madvise_funcs[DRM_XE_VMA_ATTR_PURGEABLE_STATE]
>     instead of special-case path in xe_vm_madvise_ioctl() (Matt)
>   - Track purgeable retained return via xe_madvise_details and perform
>     copy_to_user() from xe_madvise_details_fini() after locks are dropped (Matt)
>   - Set madvise_funcs[DRM_XE_VMA_ATTR_PURGEABLE_STATE] to NULL with
>     __maybe_unused on madvise_purgeable() to maintain bisectability until
>     shrinker integration is complete in final patch (Matt)
>   - Call xe_bo_recheck_purgeable_on_vma_unbind() from xe_vma_destroy()
>     right after drm_gpuva_unlink() where we already hold the BO lock,
>     drop the trylock-based late destroy path (Matt)
>   - Move purgeable_state into xe_vma_mem_attr with the other madvise
>     attributes (Matt)
>   - Drop READ_ONCE since the BO lock already protects us (Matt)
>   - Keep returning false when there are no VMAs - otherwise we'd mark
>     BOs purgeable without any user hint (Matt)
>   -  Use struct xe_vma_lock_and_validate_flags instead of multiple bool
>     parameters to improve readability and prevent argument transposition (Matt)
>   - Fix LRU crash while running shrink test
>   - Skip xe_bo_validate() for purged BOs in xe_gpuvm_validate()
>   - Split ghost BO and zero-refcount handling in xe_bo_shrink() (Thomas)
> 
> Arvind Yadav (8):
>   drm/xe/bo: Add purgeable bo state tracking and field madv to xe_bo
>   drm/xe/madvise: Implement purgeable buffer object support
>   drm/xe/bo: Handle CPU faults on purged buffer objects
>   drm/xe/vm: Prevent binding of purged buffer objects
>   drm/xe/madvise: Implement per-VMA purgeable state tracking
>   drm/xe/madvise: Block imported and exported dma-bufs
>   drm/xe/bo: Add purgeable shrinker state helpers
>   drm/xe/madvise: Enable purgeable buffer object IOCTL support
> 
> Himal Prasad Ghimiray (1):
>   drm/xe/uapi: Add UAPI support for purgeable buffer objects
> 
>  drivers/gpu/drm/xe/xe_bo.c         | 187 ++++++++++++++++++++--
>  drivers/gpu/drm/xe/xe_bo.h         |  60 +++++++
>  drivers/gpu/drm/xe/xe_bo_types.h   |   6 +
>  drivers/gpu/drm/xe/xe_pagefault.c  |  12 ++
>  drivers/gpu/drm/xe/xe_pt.c         |  40 ++++-
>  drivers/gpu/drm/xe/xe_vm.c         |  90 +++++++++--
>  drivers/gpu/drm/xe/xe_vm_madvise.c | 249 +++++++++++++++++++++++++++++
>  drivers/gpu/drm/xe/xe_vm_madvise.h |   3 +
>  drivers/gpu/drm/xe/xe_vm_types.h   |  11 ++
>  include/uapi/drm/xe_drm.h          |  44 +++++
>  10 files changed, 667 insertions(+), 35 deletions(-)
> 
> -- 
> 2.43.0
>