Re: [PATCH v4 2/8] drm/xe/bo: Add purgeable bo state tracking and field madv to xe_bo

Matthew Brost
2026-01-20T17:45:28Z

On Tue, Jan 20, 2026 at 11:38:48AM +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)
>
> v4:
> - @madv_purgeable atomic_t → u32 change across all relevant patches. (Matt)
>
> 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..00e93b3065c9 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 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 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..6acfed0c0bb4 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 */

, protected by BO's dma-resv lock.

Everything else LGTM.

Matt

> + u32 madv_purgeable;
> };
>
> #endif
> --
> 2.43.0
>