Re: [PATCH v4 6/8] drm/xe/madvise: Implement per-VMA purgeable state tracking

Yadav, Arvind
2026-01-21T05:11:36Z

On 20-01-2026 23:11, Matthew Brost wrote:
> On Tue, Jan 20, 2026 at 11:38:52AM +0530, Arvind Yadav wrote:
>> Track purgeable state per-VMA instead of using a coarse shared
>> BO check. This prevents purging shared BOs until all VMAs across
>> all VMs are marked DONTNEED.
>>
>> Add xe_bo_all_vmas_dontneed() to check all VMAs before marking
>> a BO purgeable. Add xe_bo_recheck_purgeable_on_vma_unbind() to
>> handle state transitions when VMAs are destroyed - if all
>> remaining VMAs are DONTNEED the BO can become purgeable, or if
>> no VMAs remain it transitions to WILLNEED.
>>
>> The per-VMA purgeable_state field stores the madvise hint for
>> each mapping. Shared BOs can only be purged when all VMAs
>> unanimously indicate DONTNEED.
>>
>> v3:
>> - This addresses Thomas Hellström's feedback: "loop over all vmas
>> attached to the bo and check that they all say WONTNEED. This will
>> also need a check at VMA unbinding"
>>
>> 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_vm.c | 15 +++++-
>> drivers/gpu/drm/xe/xe_vm_madvise.c | 84 +++++++++++++++++++++++++++++-
>> drivers/gpu/drm/xe/xe_vm_madvise.h | 3 ++
>> drivers/gpu/drm/xe/xe_vm_types.h | 11 ++++
>> 4 files changed, 111 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
>> index f250daae3012..9543960b5613 100644
>> --- a/drivers/gpu/drm/xe/xe_vm.c
>> +++ b/drivers/gpu/drm/xe/xe_vm.c
>> @@ -40,6 +40,7 @@
>> #include "xe_tile.h"
>> #include "xe_tlb_inval.h"
>> #include "xe_trace_bo.h"
>> +#include "xe_vm_madvise.h"
>> #include "xe_wa.h"
>>
>> static struct drm_gem_object *xe_vm_obj(struct xe_vm *vm)
>> @@ -1079,12 +1080,18 @@ static struct xe_vma *xe_vma_create(struct xe_vm *vm,
>> static void xe_vma_destroy_late(struct xe_vma *vma)
>> {
>> struct xe_vm *vm = xe_vma_vm(vma);
>> + struct xe_bo *bo = NULL;
>>
>> if (vma->ufence) {
>> xe_sync_ufence_put(vma->ufence);
>> vma->ufence = NULL;
>> }
>>
>> + /* Get BO reference for purgeable state re-check */
>> + if (!xe_vma_is_userptr(vma) && !xe_vma_is_null(vma) &&
>> + !xe_vma_is_cpu_addr_mirror(vma))
>> + bo = xe_vma_bo(vma);
> I think xe_vma_bo just returns NULL if any of the above conditions are
> met, so I believe is ok to just blindly call xe_vma_bo as you have a
> NULL check on the BO below.

Right, xe_vma_bo() already returns NULL for those cases. Will simplify
to just bo = xe_vma_bo(vma).

>
>> +
>> if (xe_vma_is_userptr(vma)) {
>> struct xe_userptr_vma *uvma = to_userptr_vma(vma);
>>
>> @@ -1093,7 +1100,13 @@ static void xe_vma_destroy_late(struct xe_vma *vma)
>> } else if (xe_vma_is_null(vma) || xe_vma_is_cpu_addr_mirror(vma)) {
>> xe_vm_put(vm);
>> } else {
>> - xe_bo_put(xe_vma_bo(vma));
>> + /* Trylock safe for async context; madvise corrects failures */
>> + if (bo && dma_resv_trylock(bo->ttm.base.resv)) {
>> + xe_bo_recheck_purgeable_on_vma_unbind(bo);
> Also I don't think the correct place to call this.
>
> I believe you can call this function in xe_vma_destroy after
> drm_gpuva_unlink. You also have BO lock there too so no need from this
> trylock path.

Good catch! Will move to xe_vma_destroy() after drm_gpuva_unlink() where
we already have the BO lock. No trylock needed there.

>> + dma_resv_unlock(bo->ttm.base.resv);
>> + }
>> +
>> + xe_bo_put(bo);
>> }
>>
>> xe_vma_free(vma);
>> diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c b/drivers/gpu/drm/xe/xe_vm_madvise.c
>> index dfeab9e24a09..27b6ad65b314 100644
>> --- a/drivers/gpu/drm/xe/xe_vm_madvise.c
>> +++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
>> @@ -12,6 +12,7 @@
>> #include "xe_pat.h"
>> #include "xe_pt.h"
>> #include "xe_svm.h"
>> +#include "xe_vm.h"
>>
>> struct xe_vmas_in_madvise_range {
>> u64 addr;
>> @@ -179,6 +180,80 @@ static void madvise_pat_index(struct xe_device *xe, struct xe_vm *vm,
>> }
>> }
>>
>> +/**
>> + * xe_bo_all_vmas_dontneed() - Check if all VMAs of a BO are marked DONTNEED
>> + * @bo: Buffer object
>> + *
>> + * Check all VMAs across all VMs to determine if BO can be purged.
>> + * Shared BOs require unanimous DONTNEED state from all mappings.
>> + *
>> + * Caller must hold BO dma-resv lock.
>> + *
>> + * Return: true if all VMAs are DONTNEED, false otherwise
>> + */
>> +static bool xe_bo_all_vmas_dontneed(struct xe_bo *bo)
>> +{
>> + struct drm_gpuvm_bo *vm_bo;
>> + struct drm_gpuva *gpuva;
>> + struct drm_gem_object *obj = &bo->ttm.base;
>> + bool has_vmas = false;
>> +
>> + dma_resv_assert_held(bo->ttm.base.resv);
>> +
>> + drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
>> + drm_gpuvm_bo_for_each_va(gpuva, vm_bo) {
>> + struct xe_vma *vma = gpuva_to_vma(gpuva);
>> +
>> + has_vmas = true;
>> +
>> + /* Any non-DONTNEED VMA prevents purging */
>> + if (READ_ONCE(vma->purgeable_state) != XE_MADV_PURGEABLE_DONTNEED)
> You don't need the READ_ONCE as purgeable_state is only accessed under
> the dma-resv lock, also there isn't a WRITE_ONCE anywhere.

Noted - I will remove READ_ONCE() - the dma-resv lock provides the
necessary protection.

>
>> + return false;
>> + }
>> + }
>> +
>> + /* No VMAs means not purgeable */
> No VMAs means it is purgeable, right?

I kept “no VMAs => not purgeable” since otherwise we can mark BOs
purgeable without any userspace DONTNEED hint (No VMAs means no user
hint at all).

>> + if (!has_vmas)
>> + return false;
>> +
>> + return true;
>> +}
>> +
>> +/**
>> + * xe_bo_recheck_purgeable_on_vma_unbind() - Re-evaluate BO purgeable state after VMA unbind
>> + * @bo: Buffer object
>> + *
>> + * When a VMA is unbound, re-check if the BO's purgeable state should change.
>> + * Destroyed VMAs may allow the BO to become purgeable if all remaining VMAs
>> + * are DONTNEED, or require transition to WILLNEED if no VMAs remain.
>> + *
>> + * Called from VMA destruction path with BO dma-resv lock held.
>> + */
>> +void xe_bo_recheck_purgeable_on_vma_unbind(struct xe_bo *bo)
>> +{
>> + if (!bo)
>> + return;
>> +
>> + dma_resv_assert_held(bo->ttm.base.resv);
>> +
>> + /*
>> + * Once purged, always purged. Cannot transition back to WILLNEED.
>> + * This matches i915 semantics where purged BOs are permanently invalid.
>> + */
>> + if (bo->madv_purgeable == XE_MADV_PURGEABLE_PURGED)
>> + return;
>> +
>> + if (xe_bo_all_vmas_dontneed(bo)) {
>> + /* All VMAs are DONTNEED - mark BO purgeable */
>> + if (bo->madv_purgeable != XE_MADV_PURGEABLE_DONTNEED)
>> + bo->madv_purgeable = XE_MADV_PURGEABLE_DONTNEED;
>> + } else {
>> + /* At least one VMA is WILLNEED - BO must not be purgeable */
>> + if (bo->madv_purgeable != XE_MADV_PURGEABLE_WILLNEED)
>> + bo->madv_purgeable = XE_MADV_PURGEABLE_WILLNEED;
>> + }
>> +}
>> +
>> /*
>> * Handle purgeable buffer object advice for DONTNEED/WILLNEED/PURGED.
>> * Returns true if any BO was purged, false otherwise.
>> @@ -213,10 +288,17 @@ static bool xe_vm_madvise_purgeable_bo(struct xe_device *xe, struct xe_vm *vm,
>>
>> switch (op->purge_state_val.val) {
>> case DRM_XE_VMA_PURGEABLE_STATE_WILLNEED:
>> + vmas[i]->purgeable_state = XE_MADV_PURGEABLE_WILLNEED;
>> +
>> + /* Mark VMA WILLNEED - BO becomes non-purgeable immediately */
>> bo->madv_purgeable = XE_MADV_PURGEABLE_WILLNEED;
>> break;
>> case DRM_XE_VMA_PURGEABLE_STATE_DONTNEED:
>> - bo->madv_purgeable = XE_MADV_PURGEABLE_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))
>> + bo->madv_purgeable = XE_MADV_PURGEABLE_DONTNEED;
>> break;
>> default:
>> drm_warn(&vm->xe->drm, "Invalid madvice value = %d\n",
>> diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.h b/drivers/gpu/drm/xe/xe_vm_madvise.h
>> index b0e1fc445f23..61868f851949 100644
>> --- a/drivers/gpu/drm/xe/xe_vm_madvise.h
>> +++ b/drivers/gpu/drm/xe/xe_vm_madvise.h
>> @@ -8,8 +8,11 @@
>>
>> struct drm_device;
>> struct drm_file;
>> +struct xe_bo;
>>
>> int xe_vm_madvise_ioctl(struct drm_device *dev, void *data,
>> struct drm_file *file);
>>
>> +void xe_bo_recheck_purgeable_on_vma_unbind(struct xe_bo *bo);
>> +
>> #endif
>> diff --git a/drivers/gpu/drm/xe/xe_vm_types.h b/drivers/gpu/drm/xe/xe_vm_types.h
>> index 437f64202f3b..94ca9d033b06 100644
>> --- a/drivers/gpu/drm/xe/xe_vm_types.h
>> +++ b/drivers/gpu/drm/xe/xe_vm_types.h
>> @@ -150,6 +150,17 @@ struct xe_vma {
>> */
>> bool skip_invalidation;
>>
>> + /**
>> + * @purgeable_state: Purgeable hint for this VMA mapping
>> + *
>> + * Per-VMA purgeable state from madvise. Valid states are WILLNEED (0)
>> + * or DONTNEED (1). Shared BOs require all VMAs to be DONTNEED before
>> + * the BO can be purged. PURGED state exists only at BO level.
>> + *
>> + * Protected by BO dma-resv lock. Set via DRM_IOCTL_XE_MADVISE.
>> + */
>> + u32 purgeable_state;
>> +
> I think xe_vma_mem_attr is a better place for this field.

Noted - I will move purgeable_state into xe_vma_mem_attr for better
organization.

Thanks,
Arvind

>
> Matt
>
>> /**
>> * @ufence: The user fence that was provided with MAP.
>> * Needs to be signalled before UNMAP can be processed.
>> --
>> 2.43.0
>>