Re: [PATCH v7 00/12] drm/xe/madvise: Add support for purgeable buffer objects

Souza, Jose
2026-03-23T15:46:16Z

On Mon, 2026-03-23 at 15:00 +0530, Arvind Yadav wrote:
> 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,
> CPU
>     and GPU fault handlers. GPU page faults on DONTNEED BOs are
> rejected in
>     xe_pagefault_begin() to preserve the GPU PTE invalidation done at
> madvise
>     time; without this the rebind path would re-map real pages and
> undo the
>     PTE zap, preventing the shrinker from ever reclaiming the BO.
>   - Correct GPU PTE zapping: madvise_purgeable() explicitly sets
>     skip_invalidation per VMA (false for DONTNEED, true for WILLNEED,
> purged
>     and dmabuf-shared BOs) so DONTNEED always triggers a GPU PTE zap
>     regardless of prior madvise state.
>   - Scratch PTE support: Fault-mode VMs use scratch pages for safe
> zero reads
>     on purged BO access.
>   - TTM shrinker integration: Encapsulated helpers manage xe_ttm_tt-
> >purgeable
>     flag and shrinker page accounting (shrinkable vs purgeable
> buckets)
>
>

uAPI patch is Acked-by: José Roberto de Souza <jose.souza@intel.com>

Mesa MR:
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40573

Thank you

>
> 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)
>
> v6 Changes (addressing Jose Souza, Thomas Hellström and Matt Brost
> feedback):
>   - Document DONTNEED blocking behavior in uAPI: Clearly describe
> which
>     operations are blocked and with what error codes. (Thomas, Matt)
>   - Block VM_BIND to DONTNEED BOs: Return -EBUSY to prevent creating
> new
>     VMAs to purgeable BOs (undefined behavior). (Thomas, Matt)
>   - Block CPU faults to DONTNEED BOs: Return VM_FAULT_SIGBUS in both
> fastpath
>     and slowpath to prevent undefined behavior. (Thomas, Matt)
>   - Block new mmap() to DONTNEED/purged BOs: Return -EBUSY for
> DONTNEED,
>     -EINVAL for PURGED. (Thomas, Matt)
>   - Block dma-buf export of DONTNEED/purged BOs: Return -EBUSY for
> DONTNEED,
>     -EINVAL for PURGED. (Thomas, Matt)
>   - Fix state transition bug: xe_bo_all_vmas_dontneed() now returns
> enum to
>     distinguish NO_VMAS (preserve state) from WILLNEED (has active
> VMAs),
>     preventing incorrect DONTNEED → WILLNEED flip on last VMA unmap
> (Matt)
>   - Set skip_invalidation explicitly in madvise_purgeable() to ensure
>     DONTNEED always zaps GPU PTEs regardless of prior madvise state.
>   - Add DRM_XE_QUERY_CONFIG_FLAG_HAS_PURGING_SUPPORT for userspace
>     feature detection. (Jose)
>
> v7 Changes (addressing Thomas Hellström, Matt B and Jose feedback):
>   - mmap check moved from xe_gem_mmap_offset_ioctl() into a new
>     xe_gem_object_mmap() callback wrapping drm_gem_ttm_mmap(), with
>     interruptible lock (Thomas)
>   - dma-buf export lock made interruptible: xe_bo_lock(bo, true)
> (Thomas)
>   - vma_lock_and_validate_flags passed by value instead of pointer
> (reviewer)
>   - xe_bo_recompute_purgeable_state() simplified using enum value
> alignment
>     between xe_bo_vmas_purge_state and xe_madv_purgeable_state, with
>     static_assert to enforce the alignment (Thomas)
>   - Merge xe_bo_set_purgeable_shrinker/xe_bo_clear_purgeable_shrinker
> into
>     a single static xe_bo_set_purgeable_shrinker(bo, new_state)
> called
>     automatically from xe_bo_set_purgeable_state() (Thomas)
>   - Drop "drm/xe/bo: Skip zero-refcount BOs in shrinker" patch —
> ghost BO
>     path already handles this correctly (Thomas)
>   - Fix Engine memory CAT errors on scratch-page VMs (Matt Roper):
>     xe_pagefault_asid_to_vm() now accepts scratch VMs via
>     || xe_vm_has_scratch(vm); xe_pagefault_begin() checks
> DONTNEED/purged
>     before validate/migrate and signals skip_rebind to caller via
> bool*
>     out-parameter to avoid xe_vma_rebind() assert and PTE zap undo
>   - Add new patch 12: Accept canonical GPU addresses in
> xe_vm_madvise_ioctl()
>     using xe_device_uncanonicalize_addr() (Matt B)
>   - UAPI doc comment improvement. (Jose)
>
> Arvind Yadav (11):
>   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: Block CPU faults to purgeable 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: Block mmap of DONTNEED/purged BOs
>   drm/xe/dma_buf: Block export of DONTNEED/purged BOs
>   drm/xe/bo: Add purgeable shrinker state helpers
>   drm/xe/madvise: Enable purgeable buffer object IOCTL support
>   drm/xe/madvise: Accept canonical GPU addresses in
> xe_vm_madvise_ioctl
>
> Himal Prasad Ghimiray (1):
>   drm/xe/uapi: Add UAPI support for purgeable buffer objects
>
>  drivers/gpu/drm/xe/xe_bo.c         | 193 +++++++++++++++++--
>  drivers/gpu/drm/xe/xe_bo.h         |  58 ++++++
>  drivers/gpu/drm/xe/xe_bo_types.h   |   6 +
>  drivers/gpu/drm/xe/xe_dma_buf.c    |  21 +++
>  drivers/gpu/drm/xe/xe_pagefault.c  |  25 ++-
>  drivers/gpu/drm/xe/xe_pt.c         |  40 +++-
>  drivers/gpu/drm/xe/xe_query.c      |   2 +
>  drivers/gpu/drm/xe/xe_svm.c        |   1 +
>  drivers/gpu/drm/xe/xe_vm.c         | 100 ++++++++--
>  drivers/gpu/drm/xe/xe_vm_madvise.c | 292
> ++++++++++++++++++++++++++++-
>  drivers/gpu/drm/xe/xe_vm_madvise.h |   3 +
>  drivers/gpu/drm/xe/xe_vm_types.h   |  11 ++
>  include/uapi/drm/xe_drm.h          |  69 +++++++
>  13 files changed, 778 insertions(+), 43 deletions(-)