Re: [PATCH v4 15/33] drm/xe: Add SVM garbage collector

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

On Wed, 2025-01-29 at 11:51 -0800, Matthew Brost wrote:
> Add basic SVM garbage collector which destroy a SVM range upon a MMU
> UNMAP event. The garbage collector runs on worker or in GPU fault
> handler and is required as locks in the path of reclaim are required
> and
> cannot be taken the notifier.
> 
> v2:
>  - Flush garbage collector in xe_svm_close
> v3:
>  - Better commit message (Thomas)
>  - Kernel doc (Thomas)
>  - Use list_first_entry_or_null for garbage collector loop (Thomas)
>  - Don't add to garbage collector if VM is closed (Thomas)
> v4:
>  - Use %pe to print error (Thomas)
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_svm.c      | 91
> +++++++++++++++++++++++++++++++-
>  drivers/gpu/drm/xe/xe_svm.h      |  5 ++
>  drivers/gpu/drm/xe/xe_vm.c       |  4 ++
>  drivers/gpu/drm/xe/xe_vm_types.h | 18 +++++++
>  4 files changed, 116 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_svm.c
> b/drivers/gpu/drm/xe/xe_svm.c
> index ace8c32f3428..3788196b2925 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -28,6 +28,7 @@ xe_svm_range_alloc(struct drm_gpusvm *gpusvm)
>  	if (!range)
>  		return ERR_PTR(-ENOMEM);
>  
> +	INIT_LIST_HEAD(&range->garbage_collector_link);
>  	xe_vm_get(gpusvm_to_vm(gpusvm));
>  
>  	return &range->base;
> @@ -44,6 +45,24 @@ static struct xe_svm_range *to_xe_range(struct
> drm_gpusvm_range *r)
>  	return container_of(r, struct xe_svm_range, base);
>  }
>  
> +static void
> +xe_svm_garbage_collector_add_range(struct xe_vm *vm, struct
> xe_svm_range *range,
> +				   const struct mmu_notifier_range
> *mmu_range)
> +{
> +	struct xe_device *xe = vm->xe;
> +
> +	drm_gpusvm_range_set_unmapped(&range->base, mmu_range);
> +
> +	spin_lock(&vm->svm.garbage_collector.lock);
> +	if (list_empty(&range->garbage_collector_link))
> +		list_add_tail(&range->garbage_collector_link,
> +			      &vm-
> >svm.garbage_collector.range_list);
> +	spin_unlock(&vm->svm.garbage_collector.lock);
> +
> +	queue_work(xe_device_get_root_tile(xe)->primary_gt-
> >usm.pf_wq,
> +		   &vm->svm.garbage_collector.work);
> +}
> +
>  static u8
>  xe_svm_range_notifier_event_begin(struct xe_vm *vm, struct
> drm_gpusvm_range *r,
>  				  const struct mmu_notifier_range
> *mmu_range,
> @@ -90,7 +109,9 @@ xe_svm_range_notifier_event_end(struct xe_vm *vm,
> struct drm_gpusvm_range *r,
>  	xe_svm_assert_in_notifier(vm);
>  
>  	drm_gpusvm_range_unmap_pages(&vm->svm.gpusvm, r, &ctx);
> -	/* TODO: Add range to garbage collector if VM is not closed
> */
> +	if (!xe_vm_is_closed(vm) && mmu_range->event ==
> MMU_NOTIFY_UNMAP)
> +		xe_svm_garbage_collector_add_range(vm,
> to_xe_range(r),
> +						   mmu_range);
>  }
>  
>  static void xe_svm_invalidate(struct drm_gpusvm *gpusvm,
> @@ -192,6 +213,63 @@ static void xe_svm_invalidate(struct drm_gpusvm
> *gpusvm,
>  		xe_svm_range_notifier_event_end(vm, r, mmu_range);
>  }
>  
> +static int __xe_svm_garbage_collector(struct xe_vm *vm,
> +				      struct xe_svm_range *range)
> +{
> +	/* TODO: Do unbind */
> +
> +	drm_gpusvm_range_remove(&vm->svm.gpusvm, &range->base);
> +
> +	return 0;
> +}
> +
> +static int xe_svm_garbage_collector(struct xe_vm *vm)
> +{
> +	struct xe_svm_range *range;
> +	int err;
> +
> +	lockdep_assert_held_write(&vm->lock);
> +
> +	if (xe_vm_is_closed_or_banned(vm))
> +		return -ENOENT;
> +
> +	spin_lock(&vm->svm.garbage_collector.lock);
> +	for (;;) {
> +		range = list_first_entry_or_null(&vm-
> >svm.garbage_collector.range_list,
> +						 typeof(*range),
> +						
> garbage_collector_link);
> +		if (!range)
> +			break;
> +
> +		list_del(&range->garbage_collector_link);
> +		spin_unlock(&vm->svm.garbage_collector.lock);
> +
> +		err = __xe_svm_garbage_collector(vm, range);
> +		if (err) {
> +			drm_warn(&vm->xe->drm,
> +				 "Garbage collection failed: %pe\n",
> +				 ERR_PTR(err));
> +			xe_vm_kill(vm, true);
> +			return err;
> +		}
> +
> +		spin_lock(&vm->svm.garbage_collector.lock);
> +	}
> +	spin_unlock(&vm->svm.garbage_collector.lock);
> +
> +	return 0;
> +}
> +
> +static void xe_svm_garbage_collector_work_func(struct work_struct
> *w)
> +{
> +	struct xe_vm *vm = container_of(w, struct xe_vm,
> +					svm.garbage_collector.work);
> +
> +	down_write(&vm->lock);
> +	xe_svm_garbage_collector(vm);
> +	up_write(&vm->lock);
> +}
> +
>  static const struct drm_gpusvm_ops gpusvm_ops = {
>  	.range_alloc = xe_svm_range_alloc,
>  	.range_free = xe_svm_range_free,
> @@ -216,6 +294,11 @@ int xe_svm_init(struct xe_vm *vm)
>  {
>  	int err;
>  
> +	spin_lock_init(&vm->svm.garbage_collector.lock);
> +	INIT_LIST_HEAD(&vm->svm.garbage_collector.range_list);
> +	INIT_WORK(&vm->svm.garbage_collector.work,
> +		  xe_svm_garbage_collector_work_func);
> +
>  	err = drm_gpusvm_init(&vm->svm.gpusvm, "Xe SVM", &vm->xe-
> >drm,
>  			      current->mm, NULL, 0, vm->size,
>  			      SZ_512M, &gpusvm_ops,
> fault_chunk_sizes,
> @@ -237,6 +320,7 @@ int xe_svm_init(struct xe_vm *vm)
>  void xe_svm_close(struct xe_vm *vm)
>  {
>  	xe_assert(vm->xe, xe_vm_is_closed(vm));
> +	flush_work(&vm->svm.garbage_collector.work);
>  }
>  
>  /**
> @@ -286,7 +370,10 @@ int xe_svm_handle_pagefault(struct xe_vm *vm,
> struct xe_vma *vma,
>  	xe_assert(vm->xe, xe_vma_is_cpu_addr_mirror(vma));
>  
>  retry:
> -	/* TODO: Run garbage collector */
> +	/* Always process UNMAPs first so view SVM ranges is current
> */
> +	err = xe_svm_garbage_collector(vm);
> +	if (err)
> +		return err;
>  
>  	r = drm_gpusvm_range_find_or_insert(&vm->svm.gpusvm,
> fault_addr,
>  					    xe_vma_start(vma),
> xe_vma_end(vma),
> diff --git a/drivers/gpu/drm/xe/xe_svm.h
> b/drivers/gpu/drm/xe/xe_svm.h
> index 03341c8547d5..ef5bc4e919e8 100644
> --- a/drivers/gpu/drm/xe/xe_svm.h
> +++ b/drivers/gpu/drm/xe/xe_svm.h
> @@ -19,6 +19,11 @@ struct xe_vma;
>  struct xe_svm_range {
>  	/** @base: base drm_gpusvm_range */
>  	struct drm_gpusvm_range base;
> +	/**
> +	 * @garbage_collector_link: Link into VM's garbage collect
> SVM range
> +	 * list. Protected by VM's garbage collect lock.
> +	 */
> +	struct list_head garbage_collector_link;
>  	/**
>  	 * @tile_present: Tile mask of binding is present for this
> range.
>  	 * Protected by GPU SVM notifier lock.
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 57083b75a602..bdc9b75e0aee 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3123,6 +3123,10 @@ int xe_vm_bind_ioctl(struct drm_device *dev,
> void *data, struct drm_file *file)
>  		}
>  	}
>  
> +	/* Ensure all UNMAPs visable */

s/visable/visible/

With that,
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

> +	if (xe_vm_in_fault_mode(vm))
> +		flush_work(&vm->svm.garbage_collector.work);
> +
>  	err = down_write_killable(&vm->lock);
>  	if (err)
>  		goto put_exec_queue;
> diff --git a/drivers/gpu/drm/xe/xe_vm_types.h
> b/drivers/gpu/drm/xe/xe_vm_types.h
> index 983f724c911b..576316729249 100644
> --- a/drivers/gpu/drm/xe/xe_vm_types.h
> +++ b/drivers/gpu/drm/xe/xe_vm_types.h
> @@ -146,6 +146,24 @@ struct xe_vm {
>  	struct {
>  		/** @svm.gpusvm: base GPUSVM used to track fault
> allocations */
>  		struct drm_gpusvm gpusvm;
> +		/**
> +		 * @svm.garbage_collector: Garbage collector which
> is used unmap
> +		 * SVM range's GPU bindings and destroy the ranges.
> +		 */
> +		struct {
> +			/** @svm.garbage_collector.lock: Protect's
> range list */
> +			spinlock_t lock;
> +			/**
> +			 * @svm.garbage_collector.range_list: List
> of SVM ranges
> +			 * in the garbage collector.
> +			 */
> +			struct list_head range_list;
> +			/**
> +			 * @svm.garbage_collector.work: Worker which
> the
> +			 * garbage collector runs on.
> +			 */
> +			struct work_struct work;
> +		} garbage_collector;
>  	} svm;
>  
>  	struct xe_device *xe;