Re: [PATCH v4 1/8] drm/xe/uapi: Add UAPI support for purgeable buffer objects

Vivi, Rodrigo
2026-01-21T18:42:33Z

On Tue, 2026-01-20 at 09:20 -0800, Matthew Brost wrote:
> On Tue, Jan 20, 2026 at 11:38:47AM +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:
> >
> > 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)
> >
> > 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 | 37
> > +++++++++++++++++++++++++++++++++++++
> >  1 file changed, 37 insertions(+)
> >
> > diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
> > index 077e66a682e2..7b3901e4b85e 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 +2190,42 @@ 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 provides a pointer to u32.
> > Kernel writes to it:
> > + * 1 if backing store exists, 0 if purged.
> > + * Similar to i915's
> > drm_i915_gem_madvise.retained field.
> > + */
> > + __u64 retained;
>
> @Rodrigo + @Thomas.
>
> Here we are adding a userptr for copying the result back to userspace
> because the existing madvise IOCTL is IOW. If we could change this
> IOCTL
> to IOWR, we could let DRM handle this for us. I'm not sure whether
> changing an IOCTL from IOW to IOWR is allowed. My understanding is
> that
> the ioctl encoding is basically the same aside from some control
> bits,
> so switching from IOW → IOWR shouldn’t break anything, but I'm
> unclear
> on the rules.

I'm not so confident it wouldn't break anything as I'm wondering if
this gets into the final number construction... and old userspace with
new kernel would hit a different slot.

>
> What do you two think?

Perhaps we would need a new ioctl and deprecate this with time?

>
> Matt
>
> > + } purge_state_val;
> >   };
> >
> >   /** @reserved: Reserved */
> > --
> > 2.43.0
> >