Re: [PATCH v5 3/9] drm/xe/madvise: Implement purgeable buffer object support

["Yadav, Arvind" <arvind.yadav@intel.com>]

On 24-02-2026 17:51, Thomas Hellström wrote:
> On Wed, 2026-02-11 at 20:56 +0530, Arvind Yadav wrote:
>> This allows userspace applications to provide memory usage hints to
>> the kernel for better memory management under pressure:
>>
>> Add the core implementation for purgeable buffer objects, enabling
>> memory
>> reclamation of user-designated DONTNEED buffers during eviction.
>>
>> This patch implements the purge operation and state machine
>> transitions:
>>
>> Purgeable States (from xe_madv_purgeable_state):
>>   - WILLNEED (0): BO should be retained, actively used
>>   - DONTNEED (1): BO eligible for purging, not currently needed
>>   - PURGED (2): BO backing store reclaimed, permanently invalid
>>
>> Design Rationale:
>>    - Async TLB invalidation via trigger_rebind (no blocking
>> xe_vm_invalidate_vma)
>>    - i915 compatibility: retained field, "once purged always purged"
>> semantics
>>    - Shared BO protection prevents multi-process memory corruption
>>    - Scratch PTE reuse avoids new infrastructure, safe for fault mode
>>
>> Note: The madvise_purgeable() function is implemented but not hooked
>> into
>> the IOCTL handler (madvise_funcs[] entry is NULL) to maintain
>> bisectability.
>> The feature will be enabled in the final patch when all supporting
>> infrastructure (shrinker, per-VMA tracking) is complete.
>>
>> v2:
>>    - 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)
>>    - Force clear_pt for non-scratch VMs to avoid phys addr 0 mapping
>> (review fix)
>>    - Add !is_purged check to resource cursor setup to prevent stale
>> access
>>
>> v3:
>>    - Rebase as xe_gt_pagefault.c is gone upstream and replaced
>>      with xe_pagefault.c (Matthew Brost)
>>    - Xe specific warn on (Matthew Brost)
>>    - Call helpers for madv_purgeable access(Matthew Brost)
>>    - Remove bo NULL check(Matthew Brost)
>>    - Use xe_bo_assert_held instead of dma assert(Matthew Brost)
>>    - Move the xe_bo_is_purged check under the dma-resv lock( by Matt)
>>    - Drop is_purged from xe_pt_stage_bind_entry and just set is_null
>> to true
>>      for purged BO rename s/is_null/is_null_or_purged (by Matt)
>>    - UAPI rule should not be changed.(Matthew Brost)
>>    - Make 'retained' a userptr (Matthew Brost)
>>
>> v4:
>>    - @madv_purgeable atomic_t → u32 change across all relevant patches
>> (Matt)
>>
>> v5:
>>    - 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)
>>    - Use put_user() instead of copy_to_user() for single u32 retained
>> value (Thomas)
>>    - Return -EFAULT from ioctl if put_user() fails (Thomas)
>>    - Validate userspace initialized retained to 0 before ioctl,
>> ensuring safe
>>      default (0 = "assume purged") if put_user() fails (Thomas)
>>    - Refactor error handling: separate fallible put_user from
>> infallible cleanup
>>    - xe_madvise_purgeable_retained_to_user(): separate helper for
>> fallible put_user
>>    - Call put_user() after releasing all locks to avoid circular
>> dependencies
>>    - Use xe_bo_move_notify() instead of xe_bo_trigger_rebind() in
>> xe_ttm_bo_purge()
>>      for proper abstraction - handles vunmap, dma-buf notifications,
>> and VRAM
>>      userfault cleanup (Thomas)
>>    - Fix LRU crash while running shrink test
>>    - Skip xe_bo_validate() for purged BOs in xe_gpuvm_validate()
>>
>> Cc: Matthew Brost <matthew.brost@intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
>> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_bo.c         | 106 ++++++++++++++++++++---
>>   drivers/gpu/drm/xe/xe_bo.h         |   2 +
>>   drivers/gpu/drm/xe/xe_pagefault.c  |  12 +++
>>   drivers/gpu/drm/xe/xe_pt.c         |  40 +++++++--
>>   drivers/gpu/drm/xe/xe_vm.c         |  20 ++++-
>>   drivers/gpu/drm/xe/xe_vm_madvise.c | 133
>> +++++++++++++++++++++++++++++
>>   6 files changed, 292 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>> index 8bf16d60b9a5..87cde4b2fe59 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.c
>> +++ b/drivers/gpu/drm/xe/xe_bo.c
>> @@ -835,6 +835,83 @@ static int xe_bo_move_notify(struct xe_bo *bo,
>>   	return 0;
>>   }
>>   
>> +/**
>> + * xe_bo_set_purgeable_state() - Set BO purgeable state with
>> validation
>> + * @bo: Buffer object
>> + * @new_state: New purgeable state
>> + *
>> + * Sets the purgeable state with lockdep assertions and validates
>> state
>> + * transitions. Once a BO is PURGED, it cannot transition to any
>> other state.
>> + * Invalid transitions are caught with xe_assert().
>> + */
>> +void xe_bo_set_purgeable_state(struct xe_bo *bo,
>> +			       enum xe_madv_purgeable_state
>> new_state)
>> +{
>> +	struct xe_device *xe = xe_bo_device(bo);
>> +
>> +	xe_bo_assert_held(bo);
>> +
>> +	/* Validate state is one of the known values */
>> +	xe_assert(xe, new_state == XE_MADV_PURGEABLE_WILLNEED ||
>> +		      new_state == XE_MADV_PURGEABLE_DONTNEED ||
>> +		      new_state == XE_MADV_PURGEABLE_PURGED);
>> +
>> +	/* Once purged, always purged - cannot transition out */
>> +	xe_assert(xe, !(bo->madv_purgeable ==
>> XE_MADV_PURGEABLE_PURGED &&
>> +			new_state != XE_MADV_PURGEABLE_PURGED));
>> +
>> +	bo->madv_purgeable = new_state;
>> +}
>> +
>> +/**
>> + * xe_ttm_bo_purge() - Purge buffer object backing store
>> + * @ttm_bo: The TTM buffer object to purge
>> + * @ctx: TTM operation context
>> + *
>> + * This function purges the backing store of a BO marked as DONTNEED
>> and
>> + * triggers rebind to invalidate stale GPU mappings. For fault-mode
>> VMs,
>> + * this zaps the PTEs. The next GPU access will trigger a page fault
>> and
>> + * perform NULL rebind (scratch pages or clear PTEs based on VM
>> config).
>> + *
>> + * Return: 0 on success, negative error code on failure
>> + */
>> +static int xe_ttm_bo_purge(struct ttm_buffer_object *ttm_bo, struct
>> ttm_operation_ctx *ctx)
>> +{
>> +	struct xe_bo *bo = ttm_to_xe_bo(ttm_bo);
>> +	struct ttm_placement place = {};
>> +	int ret;
>> +
>> +	xe_bo_assert_held(bo);
>> +
>> +	if (!ttm_bo->ttm)
>> +		return 0;
>> +
>> +	if (!xe_bo_madv_is_dontneed(bo))
>> +		return 0;
>> +
>> +	ret = ttm_bo_validate(ttm_bo, &place, ctx);
>> +	if (ret)
>> +		return ret;
>> +
>> +	/*
>> +	 * Use the standard pre-move hook so we share the same
>> cleanup/invalidate
>> +	 * path as migrations: drop any CPU vmap and schedule the
>> necessary GPU
>> +	 * unbind/rebind work.
>> +	 *
>> +	 * This may fail in no-wait contexts (fault/shrinker) or if
>> the BO is
>> +	 * pinned. Keep state unchanged on failure so we don't end
>> up "PURGED"
>> +	 * with stale mappings.
>> +	 */
>> +	ret = xe_bo_move_notify(bo, ctx);
>> +	if (ret)
>> +		return ret;
> move_notify() must be called *before* pages are actually freed, that is
> before ttm_bo_validate().


Noted,  I will move this before tttm_bo_validate().

thanks,
Arvind

>
> Other than that LGTM.
>