Re: [PATCH v5 1/9] drm/xe/uapi: Add UAPI support for purgeable buffer objects

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

On 26-02-2026 23:28, Souza, Jose wrote:
> On Wed, 2026-02-11 at 20:56 +0530, Arvind Yadav wrote:
>> From: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
>>
>> Extend the DRM_XE_MADVISE ioctl to support purgeable buffer object
>> management by adding DRM_XE_VMA_ATTR_PURGEABLE_STATE attribute type.
>>
>> This allows userspace applications to provide memory usage hints to
>> the kernel for better memory management under pressure:
>>
>> - WILLNEED: Buffer is needed and should not be purged. If the BO was
>>    previously purged, retained field returns 0 indicating backing
>> store
>>    was lost (once purged, always purged semantics matching i915).
>>
>> - DONTNEED: Buffer is not currently needed and may be purged by the
>>    kernel under memory pressure to free resources. Only applies to
>>    non-shared BOs.
>>
>> The implementation includes a 'retained' output field (matching
>> i915's
>> drm_i915_gem_madvise.retained) that indicates whether the BO's
>> backing
>> store still exists (1) or has been purged (0).
>>
>> v2:
>>    - Add PURGED state for read-only status, change ioctl to DRM_IOWR,
>>      add retained field for i915 compatibility
>>
>> v3:
>>    - UAPI rule should not be changed (Matthew Brost)
>>    - Make 'retained' a userptr (Matthew Brost)
>>
>> v4:
>>    - You cannot make this part of the union (purge_state_val) larger
>>      than the existing union (16 bytes). So just drop the '__u64
>> reserved'
>>      field. (Matt)
>>
>> v5:
>>    - Update UAPI documentation to clarify retained must be initialized
>>      to 0(Thomas)
>>
>> Cc: Matthew Brost <matthew.brost@intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Signed-off-by: Himal Prasad Ghimiray
>> <himal.prasad.ghimiray@intel.com>
>> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
>> ---
>>   include/uapi/drm/xe_drm.h | 44
>> +++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 44 insertions(+)
>>
>> diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
>> index 077e66a682e2..3e2f145e7f8f 100644
>> --- a/include/uapi/drm/xe_drm.h
>> +++ b/include/uapi/drm/xe_drm.h
>> @@ -2099,6 +2099,7 @@ struct drm_xe_madvise {
>>   #define DRM_XE_MEM_RANGE_ATTR_PREFERRED_LOC	0
>>   #define DRM_XE_MEM_RANGE_ATTR_ATOMIC		1
>>   #define DRM_XE_MEM_RANGE_ATTR_PAT		2
>> +#define DRM_XE_VMA_ATTR_PURGEABLE_STATE		3
>>   	/** @type: type of attribute */
>>   	__u32 type;
>>   
>> @@ -2189,6 +2190,49 @@ struct drm_xe_madvise {
>>   			/** @pat_index.reserved: Reserved */
>>   			__u64 reserved;
>>   		} pat_index;
>> +
>> +		/**
>> +		 * @purge_state_val: Purgeable state configuration
>> +		 *
>> +		 * Used when @type ==
>> DRM_XE_VMA_ATTR_PURGEABLE_STATE.
>> +		 *
>> +		 * Configures the purgeable state of buffer objects
>> in the specified
>> +		 * virtual address range. This allows applications
>> to hint to the kernel
>> +		 * about bo's usage patterns for better memory
>> management.
>> +		 *
>> +		 * Supported values for @purge_state_val.val:
>> +		 *  - DRM_XE_VMA_PURGEABLE_STATE_WILLNEED (0): Marks
>> BO as needed.
>> +		 *    If BO was purged, returns retained=0 (backing
>> store lost).
>> +		 *
>> +		 *  - DRM_XE_VMA_PURGEABLE_STATE_DONTNEED (1): Hints
>> that BO is not
>> +		 *    currently needed. Kernel may purge it under
>> memory pressure.
>> +		 *    Only applies to non-shared BOs. Returns
>> retained=1 if not purged.
>> +		 */
>> +		struct {
>> +#define DRM_XE_VMA_PURGEABLE_STATE_WILLNEED	0
>> +#define DRM_XE_VMA_PURGEABLE_STATE_DONTNEED	1
>> +			/** @purge_state_val.val: value for
>> DRM_XE_VMA_ATTR_PURGEABLE_STATE */
>> +			__u32 val;
>> +
>> +			/* @purge_state_val.pad */
>> +			__u32 pad;
>> +			/**
>> +			 * @purge_state_val.retained: Pointer to
>> output field for backing
>> +			 * store status.
>> +			 *
>> +			 * Userspace must initialize this field to 0
>> before the
>> +			 * ioctl. Kernel writes to it after the
>> operation:
>> +			 * - 1 if backing store exists (not purged)
>> +			 * - 0 if backing store was purged
>> +			 *
>> +			 * If userspace fails to initialize to 0,
>> ioctl returns -EINVAL.
>> +			 * This ensures a safe default (0 = assume
>> purged) if kernel
>> +			 * cannot write the result.
>> +			 *
>> +			 * Similar to i915's
>> drm_i915_gem_madvise.retained field.
>> +			 */
>> +			__u64 retained;
> why do you need a u32 pad and a u64? why not use pad and drop the last
> u64?


The __u64 retained field is a pointer to userspace memory where the 
kernel writes the output, not a direct value. Userspace pointers in uAPI 
must be __u64 to work on both 32-bit and 64-bit systems.

>
>> +		} purge_state_val;
>>   	};
> This is missing a new flag like
> DRM_XE_QUERY_CONFIG_FLAG_HAS_NO_COMPRESSION_HINT to tell UMDs if
> running Xe KMD has support for purgeable madvise.


I will add DRM_XE_QUERY_CONFIG_FLAG_HAS_PURGING for purgeable madivse 
support.

Thanks,
Arvind

>
>>   
>>   	/** @reserved: Reserved */