Re: [PATCH v3 12/17] drm/i915: Add locking to i915_gem_evict_vm()

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On Thu, 16 Dec 2021 at 14:28, Maarten Lankhorst
<maarten.lankhorst@xxxxxxxxxxxxxxx> wrote:
>
> i915_gem_evict_vm will need to be able to evict objects that are
> locked by the current ctx. By testing if the current context already
> locked the object, we can do this correctly. This allows us to
> evict the entire vm even if we already hold some objects' locks.
>
> Previously, this was spread over several commits, but it makes
> more sense to commit the changes to i915_gem_evict_vm separately
> from the changes to i915_gem_evict_something() and
> i915_gem_evict_for_node().
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> ---
>  .../gpu/drm/i915/gem/i915_gem_execbuffer.c    |  2 +-
>  drivers/gpu/drm/i915/gem/i915_gem_mman.c      |  2 +-
>  drivers/gpu/drm/i915/i915_drv.h               |  3 +-
>  drivers/gpu/drm/i915/i915_gem_evict.c         | 30 +++++++++++++++++--
>  drivers/gpu/drm/i915/i915_vma.c               |  7 ++++-
>  .../gpu/drm/i915/selftests/i915_gem_evict.c   | 10 +++++--
>  6 files changed, 46 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 2213f7b613da..eb3649e844ff 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -766,7 +766,7 @@ static int eb_reserve(struct i915_execbuffer *eb)
>                 case 1:
>                         /* Too fragmented, unbind everything and retry */
>                         mutex_lock(&eb->context->vm->mutex);
> -                       err = i915_gem_evict_vm(eb->context->vm);
> +                       err = i915_gem_evict_vm(eb->context->vm, &eb->ww);
>                         mutex_unlock(&eb->context->vm->mutex);
>                         if (err)
>                                 return err;
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> index 00cd9642669a..2856098cb449 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> @@ -366,7 +366,7 @@ static vm_fault_t vm_fault_gtt(struct vm_fault *vmf)
>                 if (vma == ERR_PTR(-ENOSPC)) {
>                         ret = mutex_lock_interruptible(&ggtt->vm.mutex);
>                         if (!ret) {
> -                               ret = i915_gem_evict_vm(&ggtt->vm);
> +                               ret = i915_gem_evict_vm(&ggtt->vm, &ww);
>                                 mutex_unlock(&ggtt->vm.mutex);
>                         }
>                         if (ret)
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index d51628d10f9d..c180019c607f 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1725,7 +1725,8 @@ int __must_check i915_gem_evict_something(struct i915_address_space *vm,
>  int __must_check i915_gem_evict_for_node(struct i915_address_space *vm,
>                                          struct drm_mm_node *node,
>                                          unsigned int flags);
> -int i915_gem_evict_vm(struct i915_address_space *vm);
> +int i915_gem_evict_vm(struct i915_address_space *vm,
> +                     struct i915_gem_ww_ctx *ww);
>
>  /* i915_gem_internal.c */
>  struct drm_i915_gem_object *
> diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
> index 2b73ddb11c66..bfd66f539fc1 100644
> --- a/drivers/gpu/drm/i915/i915_gem_evict.c
> +++ b/drivers/gpu/drm/i915/i915_gem_evict.c
> @@ -367,7 +367,7 @@ int i915_gem_evict_for_node(struct i915_address_space *vm,
>   * To clarify: This is for freeing up virtual address space, not for freeing
>   * memory in e.g. the shrinker.
>   */
> -int i915_gem_evict_vm(struct i915_address_space *vm)
> +int i915_gem_evict_vm(struct i915_address_space *vm, struct i915_gem_ww_ctx *ww)
>  {
>         int ret = 0;
>
> @@ -388,24 +388,50 @@ int i915_gem_evict_vm(struct i915_address_space *vm)
>         do {
>                 struct i915_vma *vma, *vn;
>                 LIST_HEAD(eviction_list);
> +               LIST_HEAD(locked_eviction_list);
>
>                 list_for_each_entry(vma, &vm->bound_list, vm_link) {
>                         if (i915_vma_is_pinned(vma))
>                                 continue;
>
> +                       /*
> +                        * If we already own the lock, trylock fails. In case the resv
> +                        * is shared among multiple objects, we still need the object ref.

What is "object ref" here? I assume it's just leftovers...

Otherwise,
Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>

> +                        */
> +                       if (ww && (dma_resv_locking_ctx(vma->obj->base.resv) == &ww->ctx)) {
> +                               __i915_vma_pin(vma);
> +                               list_add(&vma->evict_link, &locked_eviction_list);
> +                               continue;
> +                       }
> +
> +                       if (!i915_gem_object_trylock(vma->obj, ww))
> +                               continue;
> +
>                         __i915_vma_pin(vma);
>                         list_add(&vma->evict_link, &eviction_list);
>                 }
> -               if (list_empty(&eviction_list))
> +               if (list_empty(&eviction_list) && list_empty(&locked_eviction_list))
>                         break;
>
>                 ret = 0;
> +               /* Unbind locked objects first, before unlocking the eviction_list */
> +               list_for_each_entry_safe(vma, vn, &locked_eviction_list, evict_link) {
> +                       __i915_vma_unpin(vma);
> +
> +                       if (ret == 0)
> +                               ret = __i915_vma_unbind(vma);
> +                       if (ret != -EINTR) /* "Get me out of here!" */
> +                               ret = 0;
> +               }
> +
>                 list_for_each_entry_safe(vma, vn, &eviction_list, evict_link) {
>                         __i915_vma_unpin(vma);
>                         if (ret == 0)
>                                 ret = __i915_vma_unbind(vma);
>                         if (ret != -EINTR) /* "Get me out of here!" */
>                                 ret = 0;
> +
> +                       i915_gem_object_unlock(vma->obj);
>                 }
>         } while (ret == 0);
>
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index de24e4b3b19b..d24e90eac948 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -1462,7 +1462,12 @@ static int __i915_ggtt_pin(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
>                 /* Unlike i915_vma_pin, we don't take no for an answer! */
>                 flush_idle_contexts(vm->gt);
>                 if (mutex_lock_interruptible(&vm->mutex) == 0) {
> -                       i915_gem_evict_vm(vm);
> +                       /*
> +                        * We pass NULL ww here, as we don't want to unbind
> +                        * locked objects when called from execbuf when pinning
> +                        * is removed. This would probably regress badly.
> +                        */
> +                       i915_gem_evict_vm(vm, NULL);
>                         mutex_unlock(&vm->mutex);
>                 }
>         } while (1);
> diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_evict.c b/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> index 7e0658a77659..7178811366af 100644
> --- a/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> +++ b/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> @@ -331,6 +331,7 @@ static int igt_evict_vm(void *arg)
>  {
>         struct intel_gt *gt = arg;
>         struct i915_ggtt *ggtt = gt->ggtt;
> +       struct i915_gem_ww_ctx ww;
>         LIST_HEAD(objects);
>         int err;
>
> @@ -342,7 +343,7 @@ static int igt_evict_vm(void *arg)
>
>         /* Everything is pinned, nothing should happen */
>         mutex_lock(&ggtt->vm.mutex);
> -       err = i915_gem_evict_vm(&ggtt->vm);
> +       err = i915_gem_evict_vm(&ggtt->vm, NULL);
>         mutex_unlock(&ggtt->vm.mutex);
>         if (err) {
>                 pr_err("i915_gem_evict_vm on a full GGTT returned err=%d]\n",
> @@ -352,9 +353,14 @@ static int igt_evict_vm(void *arg)
>
>         unpin_ggtt(ggtt);
>
> +       i915_gem_ww_ctx_init(&ww, false);
>         mutex_lock(&ggtt->vm.mutex);
> -       err = i915_gem_evict_vm(&ggtt->vm);
> +       err = i915_gem_evict_vm(&ggtt->vm, &ww);
>         mutex_unlock(&ggtt->vm.mutex);
> +
> +       /* no -EDEADLK handling; can't happen with vm.mutex in place */
> +       i915_gem_ww_ctx_fini(&ww);
> +
>         if (err) {
>                 pr_err("i915_gem_evict_vm on a full GGTT returned err=%d]\n",
>                        err);
> --
> 2.34.1
>



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