Re: [PATCH v4 8/8] drm/xe/bo: Add purgeable shrinker state helpers

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

On Tue, 2026-01-20 at 09:58 -0800, Matthew Brost wrote:
> On Tue, Jan 20, 2026 at 11:38:54AM +0530, Arvind Yadav wrote:
> > Encapsulate TTM purgeable flag updates and shrinker page accounting
> > into helper functions. This prevents desynchronization between the
> > TTM tt->purgeable flag and the shrinker's page bucket counters.
> > 
> > Without these helpers, direct manipulation of xe_ttm_tt->purgeable
> > risks forgetting to update the corresponding shrinker counters,
> > leading to incorrect memory pressure calculations.
> > 
> > Add xe_bo_set_purgeable_shrinker() and
> > xe_bo_clear_purgeable_shrinker()
> > which atomically update both the TTM flag and transfer pages
> > between
> > the shrinkable and purgeable buckets.
> > 
> > v4:
> >   - @madv_purgeable atomic_t → u32 change across all relevant
> > patches. (Matt)
> > 
> > Cc: Matthew Brost <matthew.brost@intel.com>
> 
> I think this patch is right but best to double check with Thomas as
> he
> wrote the shrinker logic and is the expert here.
> 
> Matt


Looks correct to me.

@Arvind: Did you look at removing the xe_tt purgeable field (which I
always thought of as an intermediate until we had purgeable bos) and
replace it with the bo->madv_purgeable field in the shrinker code. I'm
not sure how complicated it would be, TBH but feel free to leave that
as a follow-up patch.

Also make sure the xe_bo_shrink xe_live_ktest subtest still works since
it relies heavily on shrinkable bos. I don't think CI runs it because
of the execution time and insufficient memory allocation amount
heuristics. We should also file a jira to rewrite that test to a user-
space IGT test now that we support shrinkable bos. I'll take a look at
that.

Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.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.c         | 60
> > ++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/xe/xe_bo.h         |  3 ++
> >  drivers/gpu/drm/xe/xe_vm_madvise.c | 13 +++++--
> >  3 files changed, 73 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_bo.c
> > b/drivers/gpu/drm/xe/xe_bo.c
> > index cc547915161d..2b1448ea3aed 100644
> > --- a/drivers/gpu/drm/xe/xe_bo.c
> > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > @@ -836,6 +836,66 @@ static int xe_bo_move_notify(struct xe_bo *bo,
> >  	return 0;
> >  }
> >  
> > +/**
> > + * xe_bo_set_purgeable_shrinker() - Mark BO purgeable and update
> > shrinker
> > + * @bo: Buffer object
> > + *
> > + * Transfers pages from shrinkable to purgeable bucket. Shrinker
> > can now
> > + * discard pages immediately without swapping. Caller holds BO
> > lock.
> > + */
> > +void xe_bo_set_purgeable_shrinker(struct xe_bo *bo)
> > +{
> > +	struct ttm_buffer_object *ttm_bo = &bo->ttm;
> > +	struct ttm_tt *tt = ttm_bo->ttm;
> > +	struct xe_device *xe = ttm_to_xe_device(ttm_bo->bdev);
> > +	struct xe_ttm_tt *xe_tt;
> > +
> > +	xe_bo_assert_held(bo);
> > +
> > +	if (!tt || !ttm_tt_is_populated(tt))
> > +		return;
> > +
> > +	xe_tt = container_of(tt, struct xe_ttm_tt, ttm);
> > +
> > +	if (!xe_tt->purgeable) {
> > +		xe_tt->purgeable = true;
> > +		/* Transfer pages from shrinkable to purgeable
> > count */
> > +		xe_shrinker_mod_pages(xe->mem.shrinker,
> > +				      -(long)tt->num_pages,
> > +				      tt->num_pages);
> > +	}
> > +}
> > +
> > +/**
> > + * xe_bo_clear_purgeable_shrinker() - Mark BO non-purgeable and
> > update shrinker
> > + * @bo: Buffer object
> > + *
> > + * Transfers pages from purgeable to shrinkable bucket. Shrinker
> > must now
> > + * swap pages instead of discarding. Caller holds BO lock.
> > + */
> > +void xe_bo_clear_purgeable_shrinker(struct xe_bo *bo)
> > +{
> > +	struct ttm_buffer_object *ttm_bo = &bo->ttm;
> > +	struct ttm_tt *tt = ttm_bo->ttm;
> > +	struct xe_device *xe = ttm_to_xe_device(ttm_bo->bdev);
> > +	struct xe_ttm_tt *xe_tt;
> > +
> > +	xe_bo_assert_held(bo);
> > +
> > +	if (!tt || !ttm_tt_is_populated(tt))
> > +		return;
> > +
> > +	xe_tt = container_of(tt, struct xe_ttm_tt, ttm);
> > +
> > +	if (xe_tt->purgeable) {
> > +		xe_tt->purgeable = false;
> > +		/* Transfer pages from purgeable to shrinkable
> > count */
> > +		xe_shrinker_mod_pages(xe->mem.shrinker,
> > +				      tt->num_pages,
> > +				      -(long)tt->num_pages);
> > +	}
> > +}
> > +
> >  /**
> >   * xe_ttm_bo_purge() - Purge buffer object backing store
> >   * @ttm_bo: The TTM buffer object to purge
> > diff --git a/drivers/gpu/drm/xe/xe_bo.h
> > b/drivers/gpu/drm/xe/xe_bo.h
> > index 00e93b3065c9..681495e905af 100644
> > --- a/drivers/gpu/drm/xe/xe_bo.h
> > +++ b/drivers/gpu/drm/xe/xe_bo.h
> > @@ -270,6 +270,9 @@ static inline bool
> > xe_bo_madv_is_dontneed(struct xe_bo *bo)
> >  	return bo->madv_purgeable == XE_MADV_PURGEABLE_DONTNEED;
> >  }
> >  
> > +void xe_bo_set_purgeable_shrinker(struct xe_bo *bo);
> > +void xe_bo_clear_purgeable_shrinker(struct xe_bo *bo);
> > +
> >  static inline void xe_bo_unpin_map_no_vm(struct xe_bo *bo)
> >  {
> >  	if (likely(bo)) {
> > diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c
> > b/drivers/gpu/drm/xe/xe_vm_madvise.c
> > index 5808fef89777..0fb07a1ed3ae 100644
> > --- a/drivers/gpu/drm/xe/xe_vm_madvise.c
> > +++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
> > @@ -274,12 +274,16 @@ void
> > xe_bo_recheck_purgeable_on_vma_unbind(struct xe_bo *bo)
> >  
> >  	if (xe_bo_all_vmas_dontneed(bo)) {
> >  		/* All VMAs are DONTNEED - mark BO purgeable */
> > -		if (bo->madv_purgeable !=
> > XE_MADV_PURGEABLE_DONTNEED)
> > +		if (bo->madv_purgeable !=
> > XE_MADV_PURGEABLE_DONTNEED) {
> >  			bo->madv_purgeable =
> > XE_MADV_PURGEABLE_DONTNEED;
> > +			xe_bo_set_purgeable_shrinker(bo);
> > +		}
> >  	} else {
> >  		/* At least one VMA is WILLNEED - BO must not be
> > purgeable */
> > -		if (bo->madv_purgeable !=
> > XE_MADV_PURGEABLE_WILLNEED)
> > +		if (bo->madv_purgeable !=
> > XE_MADV_PURGEABLE_WILLNEED) {
> >  			bo->madv_purgeable =
> > XE_MADV_PURGEABLE_WILLNEED;
> > +			xe_bo_clear_purgeable_shrinker(bo);
> > +		}
> >  	}
> >  }
> >  
> > @@ -325,13 +329,16 @@ static bool xe_vm_madvise_purgeable_bo(struct
> > xe_device *xe, struct xe_vm *vm,
> >  
> >  			/* Mark VMA WILLNEED - BO becomes non-
> > purgeable immediately */
> >  			bo->madv_purgeable =
> > XE_MADV_PURGEABLE_WILLNEED;
> > +			xe_bo_clear_purgeable_shrinker(bo);
> >  			break;
> >  		case DRM_XE_VMA_PURGEABLE_STATE_DONTNEED:
> >  			vmas[i]->purgeable_state =
> > XE_MADV_PURGEABLE_DONTNEED;
> >  
> >  			/* Mark BO purgeable only if all VMAs are
> > DONTNEED */
> > -			if (xe_bo_all_vmas_dontneed(bo))
> > +			if (xe_bo_all_vmas_dontneed(bo)) {
> >  				bo->madv_purgeable =
> > XE_MADV_PURGEABLE_DONTNEED;
> > +				xe_bo_set_purgeable_shrinker(bo);
> > +			}
> >  			break;
> >  		default:
> >  			drm_warn(&vm->xe->drm, "Invalid madvice
> > value = %d\n",
> > -- 
> > 2.43.0
> >