Re: [RFC v3 2/8] drm/xe/bo: Add purgeable bo state tracking and field madv to xe_bo

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

On 10-12-2025 11:16, Matthew Brost wrote:
> On Wed, Dec 10, 2025 at 10:00:46AM +0530, Arvind Yadav wrote:
>> Add infrastructure for tracking purgeable state of buffer objects.
>> This includes:
>>
>> Introduce enum xe_madv_purgeable_state with three states:
>>     - XE_MADV_PURGEABLE_WILLNEED (0): BO is needed and should not be
>>       purged. This is the default state for all BOs.
>>
>>     - XE_MADV_PURGEABLE_DONTNEED (1): BO is not currently needed and
>>       can be purged by the kernel under memory pressure to reclaim
>>       resources. Only non-shared BOs can be marked as DONTNEED.
>>
>>     - XE_MADV_PURGEABLE_PURGED (2): BO has been purged by the kernel.
>>       Accessing a purged BO results in error. Follows i915 semantics
>>       where once purged, the BO remains permanently invalid ("once
>>       purged, always purged").
>>
>> Add atomic_t madv field to struct xe_bo for state tracking
>>    of purgeable state across concurrent access paths
>>
>> v2:
>>    - Add xe_bo_is_purged() helper, improve state documentation
>>
>> V3:
>>    - Add the kernel doc(Matthew Brost)
>>    - Add the new helpers xe_bo_madv_is_dontneed(Matthew Brost)
>>
>> 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.h       | 56 ++++++++++++++++++++++++++++++++
>>   drivers/gpu/drm/xe/xe_bo_types.h |  3 ++
>>   2 files changed, 59 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_bo.h b/drivers/gpu/drm/xe/xe_bo.h
>> index 8ab4474129c3..1090a60f6ef6 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.h
>> +++ b/drivers/gpu/drm/xe/xe_bo.h
>> @@ -86,6 +86,28 @@
>>   
>>   #define XE_PCI_BARRIER_MMAP_OFFSET	(0x50 << XE_PTE_SHIFT)
>>   
>> +/**
>> + * enum xe_madv_purgeable_state - Buffer object purgeable state enumeration
>> + *
>> + * This enum defines the possible purgeable states for a buffer object,
>> + * allowing userspace to provide memory usage hints to the kernel for
>> + * better memory management under pressure.
>> + *
>> + * @XE_MADV_PURGEABLE_WILLNEED: The buffer object is needed and should not be purged.
>> + * This is the default state.
>> + * @XE_MADV_PURGEABLE_DONTNEED: The buffer object is not currently needed and can be
>> + * purged by the kernel under memory pressure.
>> + * @XE_MADV_PURGEABLE_PURGED: The buffer object has been purged by the kernel.
>> + *
>> + * Accessing a purged buffer will result in an error. Per i915 semantics,
>> + * once purged, a BO remains permanently invalid and must be destroyed and recreated.
>> + */
>> +enum xe_madv_purgeable_state {
>> +	XE_MADV_PURGEABLE_WILLNEED,
>> +	XE_MADV_PURGEABLE_DONTNEED,
>> +	XE_MADV_PURGEABLE_PURGED,
>> +};
>> +
>>   struct sg_table;
>>   
>>   struct xe_bo *xe_bo_alloc(void);
>> @@ -214,6 +236,40 @@ static inline bool xe_bo_is_protected(const struct xe_bo *bo)
>>   	return bo->pxp_key_instance;
>>   }
>>   
>> +/**
>> + * xe_bo_is_purged() - Check if buffer object has been purged
>> + * @bo: The buffer object to check
>> + *
>> + * Checks if the buffer object's backing store has been discarded by the
>> + * kernel due to memory pressure after being marked as purgeable (DONTNEED).
>> + * Once purged, the BO cannot be restored and any attempt to use it will fail.
>> + *
>> + * Context: Caller must hold the BO's dma-resv lock
>> + * Return: true if the BO has been purged, false otherwise
>> + */
>> +static inline bool xe_bo_is_purged(struct xe_bo *bo)
>> +{
>> +	xe_bo_assert_held(bo);
>> +	return atomic_read(&bo->madv_purgeable) == XE_MADV_PURGEABLE_PURGED;
>> +}
>> +
>> +/**
>> + * xe_bo_madv_is_dontneed() - Check if BO is marked as DONTNEED
>> + * @bo: The buffer object to check
>> + *
>> + * Checks if userspace has marked this BO as DONTNEED (i.e., its contents
>> + * are not currently needed and can be discarded under memory pressure).
>> + * This is used internally to decide whether a BO is eligible for purging.
>> + *
>> + * Context: Caller must hold the BO's dma-resv lock
>> + * Return: true if the BO is marked DONTNEED, false otherwise
>> + */
>> +static inline bool xe_bo_madv_is_dontneed(struct xe_bo *bo)
>> +{
>> +	xe_bo_assert_held(bo);
>> +	return atomic_read(&bo->madv_purgeable) == XE_MADV_PURGEABLE_DONTNEED;
>> +}
>> +
>>   static inline void xe_bo_unpin_map_no_vm(struct xe_bo *bo)
>>   {
>>   	if (likely(bo)) {
>> diff --git a/drivers/gpu/drm/xe/xe_bo_types.h b/drivers/gpu/drm/xe/xe_bo_types.h
>> index d4fe3c8dca5b..57b4dc7012e2 100644
>> --- a/drivers/gpu/drm/xe/xe_bo_types.h
>> +++ b/drivers/gpu/drm/xe/xe_bo_types.h
>> @@ -108,6 +108,9 @@ struct xe_bo {
>>   	 * from default
>>   	 */
>>   	u64 min_align;
>> +
>> +	/** @madv_purgeable: user space advise on BO purgeability */
>> +	atomic_t madv_purgeable;
> If this variable is only accessed under the BO's dma-resv lock, this
> doesn't need to be an atomic.
>
> So also...
>
> '@madv_purgeable: user space advise on BO purgeability, protected by
> BO's dma-resv lock'

Noted. Will do this changes.

~Arvind
> Matt
>
>>   };
>>   
>>   #endif
>> -- 
>> 2.43.0
>>