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

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Tue, 2026-01-20 at 09:45 -0800, Matthew Brost wrote:
> 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.

Agree, LGTM.

/Thomas


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