Re: [Intel-gfx] [PATCH v2 1/3] drm/i915: Introduce refcounted sg-tables

Thomas Hellström
2021-10-28T07:05:10Z

On Wed, 2021-10-27 at 19:03 +0100, Matthew Auld wrote:
> On 27/10/2021 11:52, Thomas Hellström wrote:
> > As we start to introduce asynchronous failsafe object migration,
> > where we update the object state and then submit asynchronous
> > commands we need to record what memory resources are actually used
> > by various part of the command stream. Initially for three
> > purposes:
> >
> > 1) Error capture.
> > 2) Asynchronous migration error recovery.
> > 3) Asynchronous vma bind.
> >
> > At the time where these happens, the object state may have been
> > updated
> > to be several migrations ahead and object sg-tables discarded.
> >
> > In order to make it possible to keep sg-tables with memory resource
> > information for these operations, introduce refcounted sg-tables
> > that
> > aren't freed until the last user is done with them.
> >
> > The alternative would be to reference information sitting on the
> > corresponding ttm_resources which typically have the same lifetime
> > as
> > these refcountes sg_tables, but that leads to other awkward
> > constructs:
> > Due to the design direction chosen for ttm resource managers that
> > would
> > lead to diamond-style inheritance, the LMEM resources may sometimes
> > be
> > prematurely freed, and finally the subclassed struct ttm_resource
> > would
> > have to bleed into the asynchronous vma bind code.
> >
> > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/gem/i915_gem_object.h    |   4 +-
> >   .../gpu/drm/i915/gem/i915_gem_object_types.h  |   3 +-
> >   drivers/gpu/drm/i915/gem/i915_gem_shmem.c     |  16 +-
> >   drivers/gpu/drm/i915/gem/i915_gem_ttm.c       | 188 +++++++++++--
> > -----
> >   drivers/gpu/drm/i915/i915_scatterlist.c       |  62 ++++--
> >   drivers/gpu/drm/i915/i915_scatterlist.h       |  76 ++++++-
> >   drivers/gpu/drm/i915/intel_region_ttm.c       |  15 +-
> >   drivers/gpu/drm/i915/intel_region_ttm.h       |   5 +-
> >   drivers/gpu/drm/i915/selftests/mock_region.c  |  12 +-
> >   9 files changed, 262 insertions(+), 119 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > index a5479ac7a4ad..c5ab364d4311 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > @@ -624,8 +624,8 @@ struct sg_table *shmem_alloc_st(struct
> > drm_i915_private *i915,
> >                                 size_t size, struct
> > intel_memory_region *mr,
> >                                 struct address_space *mapping,
> >                                 unsigned int max_segment);
> > -void shmem_free_st(struct sg_table *st, struct address_space
> > *mapping,
> > -                  bool dirty, bool backup);
> > +void shmem_free_st_table(struct sg_table *st, struct address_space
> > *mapping,
> > +                        bool dirty, bool backup);
>
> s/st_table/sg_table/?
>
> I thought st was shorthand for sg_table? Maybe shmem_sg_free_table?

Yes the naming is indeed a bit unfortunate here. To be consistent with
the core's sg_free_table(), I changed to
shmem_sg_free_table() / shmem_sg_alloc_table.

>
>
> >   void __shmem_writeback(size_t size, struct address_space
> > *mapping);
> >
> >   #ifdef CONFIG_MMU_NOTIFIER
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > index a4b69a43b898..604ed5ad77f5 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > @@ -544,6 +544,7 @@ struct drm_i915_gem_object {
> >                  */
> >                 struct list_head region_link;
> >
> > +               struct i915_refct_sgt *rsgt;
> >                 struct sg_table *pages;
> >                 void *mapping;
> >
> > @@ -597,7 +598,7 @@ struct drm_i915_gem_object {
> >         } mm;
> >
> >         struct {
> > -               struct sg_table *cached_io_st;
> > +               struct i915_refct_sgt *cached_io_rsgt;
> >                 struct i915_gem_object_page_iter get_io_page;
> >                 struct drm_i915_gem_object *backup;
> >                 bool created:1;
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> > b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> > index 01f332d8dbde..67c6bee695c7 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> > @@ -25,8 +25,8 @@ static void check_release_pagevec(struct pagevec
> > *pvec)
> >         cond_resched();
> >   }
> >
> > -void shmem_free_st(struct sg_table *st, struct address_space
> > *mapping,
> > -                  bool dirty, bool backup)
> > +void shmem_free_st_table(struct sg_table *st, struct address_space
> > *mapping,
> > +                        bool dirty, bool backup)
> >   {
> >         struct sgt_iter sgt_iter;
> >         struct pagevec pvec;
> > @@ -49,7 +49,6 @@ void shmem_free_st(struct sg_table *st, struct
> > address_space *mapping,
> >                 check_release_pagevec(&pvec);
> >
> >         sg_free_table(st);
> > -       kfree(st);
> >   }
> >
> >   struct sg_table *shmem_alloc_st(struct drm_i915_private *i915,
> > @@ -171,7 +170,8 @@ struct sg_table *shmem_alloc_st(struct
> > drm_i915_private *i915,
> >   err_sg:
> >         sg_mark_end(sg);
> >         if (sg != st->sgl) {
> > -               shmem_free_st(st, mapping, false, false);
> > +               shmem_free_st_table(st, mapping, false, false);
> > +               kfree(st);
> >         } else {
> >                 mapping_clear_unevictable(mapping);
> >                 sg_free_table(st);
> > @@ -254,7 +254,8 @@ static int shmem_get_pages(struct
> > drm_i915_gem_object *obj)
> >         return 0;
> >
> >   err_pages:
> > -       shmem_free_st(st, mapping, false, false);
> > +       shmem_free_st_table(st, mapping, false, false);
> > +       kfree(st);
> >         /*
> >          * shmemfs first checks if there is enough memory to
> > allocate the page
> >          * and reports ENOSPC should there be insufficient, along
> > with the usual
> > @@ -374,8 +375,9 @@ void i915_gem_object_put_pages_shmem(struct
> > drm_i915_gem_object *obj, struct sg_
> >         if (i915_gem_object_needs_bit17_swizzle(obj))
> >                 i915_gem_object_save_bit_17_swizzle(obj, pages);
> >
> > -       shmem_free_st(pages, file_inode(obj->base.filp)->i_mapping,
> > -                     obj->mm.dirty, obj->mm.madv ==
> > I915_MADV_WILLNEED);
> > +       shmem_free_st_table(pages, file_inode(obj->base.filp)-
> > >i_mapping,
> > +                           obj->mm.dirty, obj->mm.madv ==
> > I915_MADV_WILLNEED);
> > +       kfree(pages);
> >         obj->mm.dirty = false;
> >   }
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > index 4fd2edb20dd9..6826e3859e18 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > @@ -34,7 +34,7 @@
> >    * struct i915_ttm_tt - TTM page vector with additional private
> > information
> >    * @ttm: The base TTM page vector.
> >    * @dev: The struct device used for dma mapping and unmapping.
> > - * @cached_st: The cached scatter-gather table.
> > + * @cached_rsgt: The cached scatter-gather table.
> >    * @is_shmem: Set if using shmem.
> >    * @filp: The shmem file, if using shmem backend.
> >    *
> > @@ -47,7 +47,7 @@
> >   struct i915_ttm_tt {
> >         struct ttm_tt ttm;
> >         struct device *dev;
> > -       struct sg_table *cached_st;
> > +       struct i915_refct_sgt cached_rsgt;
> >
> >         bool is_shmem;
> >         struct file *filp;
> > @@ -221,14 +221,10 @@ static int i915_ttm_tt_shmem_populate(struct
> > ttm_device *bdev,
> >         if (IS_ERR(st))
> >                 return PTR_ERR(st);
> >
> > -       err = dma_map_sg_attrs(i915_tt->dev,
> > -                              st->sgl, st->nents,
> > -                              DMA_BIDIRECTIONAL,
> > -                              DMA_ATTR_SKIP_CPU_SYNC);
> > -       if (err <= 0) {
> > -               err = -EINVAL;
> > +       err = dma_map_sgtable(i915_tt->dev, st, DMA_BIDIRECTIONAL,
> > +                             DMA_ATTR_SKIP_CPU_SYNC);
> > +       if (err)
> >                 goto err_free_st;
> > -       }
> >
> >         i = 0;
> >         for_each_sgt_page(page, sgt_iter, st)
> > @@ -237,11 +233,15 @@ static int i915_ttm_tt_shmem_populate(struct
> > ttm_device *bdev,
> >         if (ttm->page_flags & TTM_TT_FLAG_SWAPPED)
> >                 ttm->page_flags &= ~TTM_TT_FLAG_SWAPPED;
> >
> > -       i915_tt->cached_st = st;
> > +       i915_tt->cached_rsgt.table = *st;
> > +       kfree(st);
>
> Will it work if the above just operates on the rsgt.table?

I'll change the shmem utility here to not allocate the struct sg_table
and then we can operate on it directly.

>
> > +
> >         return 0;
> >
> >   err_free_st:
> > -       shmem_free_st(st, filp->f_mapping, false, false);
> > +       shmem_free_st_table(st, filp->f_mapping, false, false);
> > +       kfree(st);
> > +
> >         return err;
> >   }
> >
> > @@ -249,16 +249,29 @@ static void
> > i915_ttm_tt_shmem_unpopulate(struct ttm_tt *ttm)
> >   {
> >         struct i915_ttm_tt *i915_tt = container_of(ttm,
> > typeof(*i915_tt), ttm);
> >         bool backup = ttm->page_flags & TTM_TT_FLAG_SWAPPED;
> > +       struct sg_table *st = &i915_tt->cached_rsgt.table;
> >
> > -       dma_unmap_sg(i915_tt->dev, i915_tt->cached_st->sgl,
> > -                    i915_tt->cached_st->nents,
> > -                    DMA_BIDIRECTIONAL);
> > +       if (st->sgl)
>
> Can we ever hit this? I would have presumed not? Below also.

Yes, here's where we typically free the scatterlist.

>
> > +               shmem_free_st_table(st,
> > +                                   file_inode(i915_tt->filp)-
> > >i_mapping,
> > +                                   backup, backup);
> > +}
> >
> > -       shmem_free_st(fetch_and_zero(&i915_tt->cached_st),
> > -                     file_inode(i915_tt->filp)->i_mapping,
> > -                     backup, backup);
> > +static void i915_ttm_tt_release(struct kref *ref)
> > +{
> > +       struct i915_ttm_tt *i915_tt =
> > +               container_of(ref, typeof(*i915_tt),
> > cached_rsgt.kref);
> > +       struct sg_table *st = &i915_tt->cached_rsgt.table;
> > +
> > +       GEM_WARN_ON(st->sgl);
> > +
> > +       kfree(i915_tt);
> >   }
> >
> > +static const struct i915_refct_sgt_ops tt_rsgt_ops = {
> > +       .release = i915_ttm_tt_release
> > +};
> > +
> >   static struct ttm_tt *i915_ttm_tt_create(struct ttm_buffer_object
> > *bo,
> >                                          uint32_t page_flags)
> >   {
> > @@ -287,6 +300,9 @@ static struct ttm_tt *i915_ttm_tt_create(struct
> > ttm_buffer_object *bo,
> >         if (ret)
> >                 goto err_free;
> >
> > +       i915_refct_sgt_init_ops(&i915_tt->cached_rsgt, bo-
> > >base.size,
> > +                               &tt_rsgt_ops);
> > +
> >         i915_tt->dev = obj->base.dev->dev;
> >
> >         return &i915_tt->ttm;
> > @@ -311,17 +327,15 @@ static int i915_ttm_tt_populate(struct
> > ttm_device *bdev,
> >   static void i915_ttm_tt_unpopulate(struct ttm_device *bdev,
> > struct ttm_tt *ttm)
> >   {
> >         struct i915_ttm_tt *i915_tt = container_of(ttm,
> > typeof(*i915_tt), ttm);
> > +       struct sg_table *st = &i915_tt->cached_rsgt.table;
> > +
> > +       if (st->sgl)
> > +               dma_unmap_sgtable(i915_tt->dev, st,
> > DMA_BIDIRECTIONAL, 0);
> >
> >         if (i915_tt->is_shmem) {
> >                 i915_ttm_tt_shmem_unpopulate(ttm);
> >         } else {
> > -               if (i915_tt->cached_st) {
> > -                       dma_unmap_sgtable(i915_tt->dev, i915_tt-
> > >cached_st,
> > -                                         DMA_BIDIRECTIONAL, 0);
> > -                       sg_free_table(i915_tt->cached_st);
> > -                       kfree(i915_tt->cached_st);
> > -                       i915_tt->cached_st = NULL;
> > -               }
> > +               sg_free_table(st);
> >                 ttm_pool_free(&bdev->pool, ttm);
> >         }
> >   }
> > @@ -334,7 +348,7 @@ static void i915_ttm_tt_destroy(struct
> > ttm_device *bdev, struct ttm_tt *ttm)
> >                 fput(i915_tt->filp);
> >
> >         ttm_tt_fini(ttm);
> > -       kfree(i915_tt);
> > +       i915_refct_sgt_put(&i915_tt->cached_rsgt);
> >   }
> >
> >   static bool i915_ttm_eviction_valuable(struct ttm_buffer_object
> > *bo,
> > @@ -376,12 +390,12 @@ static int i915_ttm_move_notify(struct
> > ttm_buffer_object *bo)
> >         return 0;
> >   }
> >
> > -static void i915_ttm_free_cached_io_st(struct drm_i915_gem_object
> > *obj)
> > +static void i915_ttm_free_cached_io_rsgt(struct
> > drm_i915_gem_object *obj)
> >   {
> >         struct radix_tree_iter iter;
> >         void __rcu **slot;
> >
> > -       if (!obj->ttm.cached_io_st)
> > +       if (!obj->ttm.cached_io_rsgt)
> >                 return;
> >
> >         rcu_read_lock();
> > @@ -389,9 +403,8 @@ static void i915_ttm_free_cached_io_st(struct
> > drm_i915_gem_object *obj)
> >                 radix_tree_delete(&obj->ttm.get_io_page.radix,
> > iter.index);
> >         rcu_read_unlock();
> >
> > -       sg_free_table(obj->ttm.cached_io_st);
> > -       kfree(obj->ttm.cached_io_st);
> > -       obj->ttm.cached_io_st = NULL;
> > +       i915_refct_sgt_put(obj->ttm.cached_io_rsgt);
> > +       obj->ttm.cached_io_rsgt = NULL;
> >   }
> >
> >   static void
> > @@ -477,7 +490,7 @@ static int i915_ttm_purge(struct
> > drm_i915_gem_object *obj)
> >         obj->write_domain = 0;
> >         obj->read_domains = 0;
> >         i915_ttm_adjust_gem_after_move(obj);
> > -       i915_ttm_free_cached_io_st(obj);
> > +       i915_ttm_free_cached_io_rsgt(obj);
> >         obj->mm.madv = __I915_MADV_PURGED;
> >         return 0;
> >   }
> > @@ -532,7 +545,7 @@ static void i915_ttm_swap_notify(struct
> > ttm_buffer_object *bo)
> >         int ret = i915_ttm_move_notify(bo);
> >
> >         GEM_WARN_ON(ret);
> > -       GEM_WARN_ON(obj->ttm.cached_io_st);
> > +       GEM_WARN_ON(obj->ttm.cached_io_rsgt);
> >         if (!ret && obj->mm.madv != I915_MADV_WILLNEED)
> >                 i915_ttm_purge(obj);
> >   }
> > @@ -543,7 +556,7 @@ static void i915_ttm_delete_mem_notify(struct
> > ttm_buffer_object *bo)
> >
> >         if (likely(obj)) {
> >                 __i915_gem_object_pages_fini(obj);
> > -               i915_ttm_free_cached_io_st(obj);
> > +               i915_ttm_free_cached_io_rsgt(obj);
> >         }
> >   }
> >
> > @@ -563,40 +576,35 @@ i915_ttm_region(struct ttm_device *bdev, int
> > ttm_mem_type)
> >                                           ttm_mem_type -
> > I915_PL_LMEM0);
> >   }
> >
> > -static struct sg_table *i915_ttm_tt_get_st(struct ttm_tt *ttm)
> > +static struct i915_refct_sgt *i915_ttm_tt_get_st(struct ttm_tt
> > *ttm)
> >   {
> >         struct i915_ttm_tt *i915_tt = container_of(ttm,
> > typeof(*i915_tt), ttm);
> >         struct sg_table *st;
> >         int ret;
> >
> > -       if (i915_tt->cached_st)
> > -               return i915_tt->cached_st;
> > -
> > -       st = kzalloc(sizeof(*st), GFP_KERNEL);
> > -       if (!st)
> > -               return ERR_PTR(-ENOMEM);
> > +       if (i915_tt->cached_rsgt.table.sgl)
> > +               return i915_refct_sgt_get(&i915_tt->cached_rsgt);
> >
> > +       st = &i915_tt->cached_rsgt.table;
> >         ret = sg_alloc_table_from_pages_segment(st,
> >                         ttm->pages, ttm->num_pages,
> >                         0, (unsigned long)ttm->num_pages <<
> > PAGE_SHIFT,
> >                         i915_sg_segment_size(), GFP_KERNEL);
> >         if (ret) {
> > -               kfree(st);
> > +               st->sgl = NULL;
> >                 return ERR_PTR(ret);
> >         }
> >
> >         ret = dma_map_sgtable(i915_tt->dev, st, DMA_BIDIRECTIONAL,
> > 0);
> >         if (ret) {
> >                 sg_free_table(st);
> > -               kfree(st);
> >                 return ERR_PTR(ret);
> >         }
> >
> > -       i915_tt->cached_st = st;
> > -       return st;
> > +       return i915_refct_sgt_get(&i915_tt->cached_rsgt);
> >   }
> >
> > -static struct sg_table *
> > +static struct i915_refct_sgt *
> >   i915_ttm_resource_get_st(struct drm_i915_gem_object *obj,
> >                          struct ttm_resource *res)
> >   {
> > @@ -610,7 +618,21 @@ i915_ttm_resource_get_st(struct
> > drm_i915_gem_object *obj,
> >          * the resulting st. Might make sense for GGTT.
> >          */
> >         GEM_WARN_ON(!cpu_maps_iomem(res));
> > -       return intel_region_ttm_resource_to_st(obj->mm.region,
> > res);
> > +       if (bo->resource == res) {
> > +               if (!obj->ttm.cached_io_rsgt) {
> > +                       struct i915_refct_sgt *rsgt;
> > +
> > +                       rsgt =
> > intel_region_ttm_resource_to_rsgt(obj->mm.region,
> > +
> > res);
> > +                       if (IS_ERR(rsgt))
> > +                               return rsgt;
> > +
> > +                       obj->ttm.cached_io_rsgt = rsgt;
> > +               }
> > +               return i915_refct_sgt_get(obj->ttm.cached_io_rsgt);
> > +       }
> > +
> > +       return intel_region_ttm_resource_to_rsgt(obj->mm.region,
> > res);
> >   }
> >
> >   static int i915_ttm_accel_move(struct ttm_buffer_object *bo,
> > @@ -621,10 +643,7 @@ static int i915_ttm_accel_move(struct
> > ttm_buffer_object *bo,
> >   {
> >         struct drm_i915_private *i915 = container_of(bo->bdev,
> > typeof(*i915),
> >                                                      bdev);
> > -       struct ttm_resource_manager *src_man =
> > -               ttm_manager_type(bo->bdev, bo->resource->mem_type);
> >         struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
> > -       struct sg_table *src_st;
> >         struct i915_request *rq;
> >         struct ttm_tt *src_ttm = bo->ttm;
> >         enum i915_cache_level src_level, dst_level;
> > @@ -650,17 +669,22 @@ static int i915_ttm_accel_move(struct
> > ttm_buffer_object *bo,
> >                 }
> >                 intel_engine_pm_put(i915->gt.migrate.context-
> > >engine);
> >         } else {
> > -               src_st = src_man->use_tt ?
> > i915_ttm_tt_get_st(src_ttm) :
> > -                       obj->ttm.cached_io_st;
> > +               struct i915_refct_sgt *src_rsgt =
> > +                       i915_ttm_resource_get_st(obj, bo-
> > >resource);
> > +
> > +               if (IS_ERR(src_rsgt))
> > +                       return PTR_ERR(src_rsgt);
> >
> >                 src_level = i915_ttm_cache_level(i915, bo-
> > >resource, src_ttm);
> >                 intel_engine_pm_get(i915->gt.migrate.context-
> > >engine);
> >                 ret = intel_context_migrate_copy(i915-
> > >gt.migrate.context,
> > -                                                NULL, src_st->sgl,
> > src_level,
> > +                                                NULL, src_rsgt-
> > >table.sgl,
> > +                                                src_level,
> >
> > gpu_binds_iomem(bo->resource),
> >                                                  dst_st->sgl,
> > dst_level,
> >
> > gpu_binds_iomem(dst_mem),
> >                                                  &rq);
> > +               i915_refct_sgt_put(src_rsgt);
> >                 if (!ret && rq) {
> >                         i915_request_wait(rq, 0,
> > MAX_SCHEDULE_TIMEOUT);
> >                         i915_request_put(rq);
> > @@ -674,13 +698,14 @@ static int i915_ttm_accel_move(struct
> > ttm_buffer_object *bo,
> >   static void __i915_ttm_move(struct ttm_buffer_object *bo, bool
> > clear,
> >                             struct ttm_resource *dst_mem,
> >                             struct ttm_tt *dst_ttm,
> > -                           struct sg_table *dst_st,
> > +                           struct i915_refct_sgt *dst_rsgt,
> >                             bool allow_accel)
> >   {
> >         int ret = -EINVAL;
> >
> >         if (allow_accel)
> > -               ret = i915_ttm_accel_move(bo, clear, dst_mem,
> > dst_ttm, dst_st);
> > +               ret = i915_ttm_accel_move(bo, clear, dst_mem,
> > dst_ttm,
> > +                                         &dst_rsgt->table);
> >         if (ret) {
> >                 struct drm_i915_gem_object *obj =
> > i915_ttm_to_gem(bo);
> >                 struct intel_memory_region *dst_reg, *src_reg;
> > @@ -697,12 +722,13 @@ static void __i915_ttm_move(struct
> > ttm_buffer_object *bo, bool clear,
> >                 dst_iter = !cpu_maps_iomem(dst_mem) ?
> >                         ttm_kmap_iter_tt_init(&_dst_iter.tt,
> > dst_ttm) :
> >                         ttm_kmap_iter_iomap_init(&_dst_iter.io,
> > &dst_reg->iomap,
> > -                                                dst_st, dst_reg-
> > >region.start);
> > +                                                &dst_rsgt->table,
> > +                                                dst_reg-
> > >region.start);
> >
> >                 src_iter = !cpu_maps_iomem(bo->resource) ?
> >                         ttm_kmap_iter_tt_init(&_src_iter.tt, bo-
> > >ttm) :
> >                         ttm_kmap_iter_iomap_init(&_src_iter.io,
> > &src_reg->iomap,
> > -                                                obj-
> > >ttm.cached_io_st,
> > +                                                &obj-
> > >ttm.cached_io_rsgt->table,
> >                                                  src_reg-
> > >region.start);
> >
> >                 ttm_move_memcpy(clear, dst_mem->num_pages,
> > dst_iter, src_iter);
> > @@ -718,7 +744,7 @@ static int i915_ttm_move(struct
> > ttm_buffer_object *bo, bool evict,
> >         struct ttm_resource_manager *dst_man =
> >                 ttm_manager_type(bo->bdev, dst_mem->mem_type);
> >         struct ttm_tt *ttm = bo->ttm;
> > -       struct sg_table *dst_st;
> > +       struct i915_refct_sgt *dst_rsgt;
> >         bool clear;
> >         int ret;
> >
> > @@ -744,22 +770,24 @@ static int i915_ttm_move(struct
> > ttm_buffer_object *bo, bool evict,
> >                         return ret;
> >         }
> >
> > -       dst_st = i915_ttm_resource_get_st(obj, dst_mem);
> > -       if (IS_ERR(dst_st))
> > -               return PTR_ERR(dst_st);
> > +       dst_rsgt = i915_ttm_resource_get_st(obj, dst_mem);
> > +       if (IS_ERR(dst_rsgt))
> > +               return PTR_ERR(dst_rsgt);
> >
> >         clear = !cpu_maps_iomem(bo->resource) && (!ttm ||
> > !ttm_tt_is_populated(ttm));
> >         if (!(clear && ttm && !(ttm->page_flags &
> > TTM_TT_FLAG_ZERO_ALLOC)))
> > -               __i915_ttm_move(bo, clear, dst_mem, bo->ttm,
> > dst_st, true);
> > +               __i915_ttm_move(bo, clear, dst_mem, bo->ttm,
> > dst_rsgt, true);
> >
> >         ttm_bo_move_sync_cleanup(bo, dst_mem);
> >         i915_ttm_adjust_domains_after_move(obj);
> > -       i915_ttm_free_cached_io_st(obj);
> > +       i915_ttm_free_cached_io_rsgt(obj);
> >
> >         if (gpu_binds_iomem(dst_mem) || cpu_maps_iomem(dst_mem)) {
> > -               obj->ttm.cached_io_st = dst_st;
> > -               obj->ttm.get_io_page.sg_pos = dst_st->sgl;
> > +               obj->ttm.cached_io_rsgt = dst_rsgt;
> > +               obj->ttm.get_io_page.sg_pos = dst_rsgt->table.sgl;
> >                 obj->ttm.get_io_page.sg_idx = 0;
> > +       } else {
> > +               i915_refct_sgt_put(dst_rsgt);
> >         }
> >
> >         i915_ttm_adjust_lru(obj);
> > @@ -825,7 +853,6 @@ static int __i915_ttm_get_pages(struct
> > drm_i915_gem_object *obj,
> >                 .interruptible = true,
> >                 .no_wait_gpu = false,
> >         };
> > -       struct sg_table *st;
> >         int real_num_busy;
> >         int ret;
> >
> > @@ -862,12 +889,16 @@ static int __i915_ttm_get_pages(struct
> > drm_i915_gem_object *obj,
> >         }
> >
> >         if (!i915_gem_object_has_pages(obj)) {
> > -               /* Object either has a page vector or is an iomem
> > object */
> > -               st = bo->ttm ? i915_ttm_tt_get_st(bo->ttm) : obj-
> > >ttm.cached_io_st;
> > -               if (IS_ERR(st))
> > -                       return PTR_ERR(st);
> > +               struct i915_refct_sgt *rsgt =
> > +                       i915_ttm_resource_get_st(obj, bo-
> > >resource);
> > +
> > +               if (IS_ERR(rsgt))
> > +                       return PTR_ERR(rsgt);
> >
> > -               __i915_gem_object_set_pages(obj, st,
> > i915_sg_dma_sizes(st->sgl));
> > +               GEM_BUG_ON(obj->mm.rsgt);
> > +               obj->mm.rsgt = rsgt;
> > +               __i915_gem_object_set_pages(obj, &rsgt->table,
> > +                                           i915_sg_dma_sizes(rsgt-
> > >table.sgl));
> >         }
> >
> >         i915_ttm_adjust_lru(obj);
> > @@ -941,6 +972,13 @@ static void i915_ttm_put_pages(struct
> > drm_i915_gem_object *obj,
> >          * If the object is not destroyed next, The TTM eviction
> > logic
> >          * and shrinkers will move it out if needed.
> >          */
> > +
> > +       if (obj->mm.rsgt) {
> > +               i915_refct_sgt_put(obj->mm.rsgt);
> > +               obj->mm.rsgt = NULL;
> > +       }
>
> i915_refct_sgt_put(fetch_and_zero(&obj->mm.rsgt)) ?
>
> > +
> > +       i915_ttm_adjust_lru(obj);
>
> Unrelated change, or do I need to look closer?

No that's unrelated. Probably a rebase mistake. Will remove.

>
> >   }
> >
> >   static void i915_ttm_adjust_lru(struct drm_i915_gem_object *obj)
> > @@ -1278,7 +1316,7 @@ int i915_gem_obj_copy_ttm(struct
> > drm_i915_gem_object *dst,
> >         struct ttm_operation_ctx ctx = {
> >                 .interruptible = intr,
> >         };
> > -       struct sg_table *dst_st;
> > +       struct i915_refct_sgt *dst_rsgt;
> >         int ret;
> >
> >         assert_object_held(dst);
> > @@ -1293,11 +1331,11 @@ int i915_gem_obj_copy_ttm(struct
> > drm_i915_gem_object *dst,
> >         if (ret)
> >                 return ret;
> >
> > -       dst_st = gpu_binds_iomem(dst_bo->resource) ?
> > -               dst->ttm.cached_io_st : i915_ttm_tt_get_st(dst_bo-
> > >ttm);
> > -
> > +       dst_rsgt = i915_ttm_resource_get_st(dst, dst_bo->resource);
> >         __i915_ttm_move(src_bo, false, dst_bo->resource, dst_bo-
> > >ttm,
> > -                       dst_st, allow_accel);
> > +                       dst_rsgt, allow_accel);
> > +
> > +       i915_refct_sgt_put(dst_rsgt);
> >
> >         return 0;
> >   }
> > diff --git a/drivers/gpu/drm/i915/i915_scatterlist.c
> > b/drivers/gpu/drm/i915/i915_scatterlist.c
> > index 4a6712dca838..8a510ee5d1ad 100644
> > --- a/drivers/gpu/drm/i915/i915_scatterlist.c
> > +++ b/drivers/gpu/drm/i915/i915_scatterlist.c
> > @@ -41,8 +41,32 @@ bool i915_sg_trim(struct sg_table *orig_st)
> >         return true;
> >   }
> >
> > +static void i915_refct_sgt_release(struct kref *ref)
> > +{
> > +       struct i915_refct_sgt *rsgt =
> > +               container_of(ref, typeof(*rsgt), kref);
> > +
> > +       sg_free_table(&rsgt->table);
> > +       kfree(rsgt);
> > +}
> > +
> > +static const struct i915_refct_sgt_ops rsgt_ops = {
> > +       .release = i915_refct_sgt_release
> > +};
> > +
> > +/**
> > + * i915_refct_sgt_init - Initialize a struct i915_refct_sgt with
> > default ops
> > + * @rsgt: The struct i915_refct_sgt to initialize.
> > + * size: The size of the underlying memory buffer.
> > + */
> > +void i915_refct_sgt_init(struct i915_refct_sgt *rsgt, size_t size)
> > +{
> > +       i915_refct_sgt_init_ops(rsgt, size, &rsgt_ops);
> > +}
> > +
> >   /**
> > - * i915_sg_from_mm_node - Create an sg_table from a struct
> > drm_mm_node
> > + * i915_rsgt_from_mm_node - Create a refcounted sg_table from a
> > struct
> > + * drm_mm_node
> >    * @node: The drm_mm_node.
> >    * @region_start: An offset to add to the dma addresses of the sg
> > list.
> >    *
> > @@ -50,25 +74,28 @@ bool i915_sg_trim(struct sg_table *orig_st)
> >    * taking a maximum segment length into account, splitting into
> > segments
> >    * if necessary.
> >    *
> > - * Return: A pointer to a kmalloced struct sg_table on success,
> > negative
> > + * Return: A pointer to a kmalloced struct i915_refct_sgt on
> > success, negative
> >    * error code cast to an error pointer on failure.
> >    */
> > -struct sg_table *i915_sg_from_mm_node(const struct drm_mm_node
> > *node,
> > -                                     u64 region_start)
> > +struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct
> > drm_mm_node *node,
> > +                                             u64 region_start)
> >   {
> >         const u64 max_segment = SZ_1G; /* Do we have a limit on
> > this? */
> >         u64 segment_pages = max_segment >> PAGE_SHIFT;
> >         u64 block_size, offset, prev_end;
> > +       struct i915_refct_sgt *rsgt;
> >         struct sg_table *st;
> >         struct scatterlist *sg;
> >
> > -       st = kmalloc(sizeof(*st), GFP_KERNEL);
> > -       if (!st)
> > +       rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL);
> > +       if (!rsgt)
> >                 return ERR_PTR(-ENOMEM);
> >
> > +       i915_refct_sgt_init(rsgt, node->size << PAGE_SHIFT);
> > +       st = &rsgt->table;
> >         if (sg_alloc_table(st, DIV_ROUND_UP(node->size,
> > segment_pages),
> >                            GFP_KERNEL)) {
> > -               kfree(st);
> > +               i915_refct_sgt_put(rsgt);
> >                 return ERR_PTR(-ENOMEM);
> >         }
> >
> > @@ -104,11 +131,11 @@ struct sg_table *i915_sg_from_mm_node(const
> > struct drm_mm_node *node,
> >         sg_mark_end(sg);
> >         i915_sg_trim(st);
> >
> > -       return st;
> > +       return rsgt;
> >   }
> >
> >   /**
> > - * i915_sg_from_buddy_resource - Create an sg_table from a struct
> > + * i915_rsgt_from_buddy_resource - Create a refcounted sg_table
> > from a struct
> >    * i915_buddy_block list
> >    * @res: The struct i915_ttm_buddy_resource.
> >    * @region_start: An offset to add to the dma addresses of the sg
> > list.
> > @@ -117,11 +144,11 @@ struct sg_table *i915_sg_from_mm_node(const
> > struct drm_mm_node *node,
> >    * taking a maximum segment length into account, splitting into
> > segments
> >    * if necessary.
> >    *
> > - * Return: A pointer to a kmalloced struct sg_table on success,
> > negative
> > + * Return: A pointer to a kmalloced struct i915_refct_sgts on
> > success, negative
> >    * error code cast to an error pointer on failure.
> >    */
> > -struct sg_table *i915_sg_from_buddy_resource(struct ttm_resource
> > *res,
> > -                                            u64 region_start)
> > +struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct
> > ttm_resource *res,
> > +                                                    u64
> > region_start)
> >   {
> >         struct i915_ttm_buddy_resource *bman_res =
> > to_ttm_buddy_resource(res);
> >         const u64 size = res->num_pages << PAGE_SHIFT;
> > @@ -129,18 +156,21 @@ struct sg_table
> > *i915_sg_from_buddy_resource(struct ttm_resource *res,
> >         struct i915_buddy_mm *mm = bman_res->mm;
> >         struct list_head *blocks = &bman_res->blocks;
> >         struct i915_buddy_block *block;
> > +       struct i915_refct_sgt *rsgt;
> >         struct scatterlist *sg;
> >         struct sg_table *st;
> >         resource_size_t prev_end;
> >
> >         GEM_BUG_ON(list_empty(blocks));
> >
> > -       st = kmalloc(sizeof(*st), GFP_KERNEL);
> > -       if (!st)
> > +       rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL);
> > +       if (!rsgt)
> >                 return ERR_PTR(-ENOMEM);
> >
> > +       i915_refct_sgt_init(rsgt, size);
> > +       st = &rsgt->table;
> >         if (sg_alloc_table(st, res->num_pages, GFP_KERNEL)) {
> > -               kfree(st);
> > +               i915_refct_sgt_put(rsgt);
> >                 return ERR_PTR(-ENOMEM);
> >         }
> >
> > @@ -181,7 +211,7 @@ struct sg_table
> > *i915_sg_from_buddy_resource(struct ttm_resource *res,
> >         sg_mark_end(sg);
> >         i915_sg_trim(st);
> >
> > -       return st;
> > +       return rsgt;
> >   }
> >
> >   #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
> > diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h
> > b/drivers/gpu/drm/i915/i915_scatterlist.h
> > index b8bd5925b03f..321fd4a9f777 100644
> > --- a/drivers/gpu/drm/i915/i915_scatterlist.h
> > +++ b/drivers/gpu/drm/i915/i915_scatterlist.h
> > @@ -144,10 +144,78 @@ static inline unsigned int
> > i915_sg_segment_size(void)
> >
> >   bool i915_sg_trim(struct sg_table *orig_st);
> >
> > -struct sg_table *i915_sg_from_mm_node(const struct drm_mm_node
> > *node,
> > -                                     u64 region_start);
> > +/**
> > + * struct i915_refct_sgt_ops - Operations structure for struct
> > i915_refct_sgt
> > + */
> > +struct i915_refct_sgt_ops {
> > +       /**
> > +        * release() - Free the memory of the struct i915_refct_sgt
> > +        * @ref: struct kref that is embedded in the struct
> > i915_refct_sgt
> > +        */
> > +       void (*release)(struct kref *ref);
> > +};
> > +
> > +/**
> > + * struct i915_refct_sgt - A refcounted scatter-gather table
> > + * @kref: struct kref for refcounting
> > + * @table: struct sg_table holding the scatter-gather table
> > itself. Note that
> > + * @table->sgl = NULL can be used to determine whether a scatter-
> > gather table
> > + * is present or not.
> > + * @size: The size in bytes of the underlying memory buffer
> > + * @ops: The operations structure.
> > + */
> > +struct i915_refct_sgt {
> > +       struct kref kref;
> > +       struct sg_table table;
> > +       size_t size;
> > +       const struct i915_refct_sgt_ops *ops;
> > +};
> > +
> > +/**
> > + * i915_refct_sgt_put - Put a refcounted sg-table
> > + * @rsgt the struct i915_refct_sgt to put.
> > + */
> > +static inline void i915_refct_sgt_put(struct i915_refct_sgt *rsgt)
> > +{
> > +       if (rsgt)
> > +               kref_put(&rsgt->kref, rsgt->ops->release);
> > +}
> > +
> > +/**
> > + * i915_refct_sgt_get - Get a refcounted sg-table
> > + * @rsgt the struct i915_refct_sgt to get.
> > + */
> > +static inline struct i915_refct_sgt *
> > +i915_refct_sgt_get(struct i915_refct_sgt *rsgt)
> > +{
> > +       kref_get(&rsgt->kref);
> > +       return rsgt;
> > +}
> > +
> > +/**
> > + * i915_refct_sgt_init_ops - Initialize a refcounted sg-list with
> > a custom
> > + * operations structure
> > + * @rsgt The struct i915_refct_sgt to initialize.
> > + * @size: Size in bytes of the underlying memory buffer.
> > + * @ops: A customized operations structure in case the refcounted
> > sg-list
> > + * is embedded into another structure.
> > + */
> > +static inline void i915_refct_sgt_init_ops(struct i915_refct_sgt
> > *rsgt,
> > +                                          size_t size,
> > +                                          const struct
> > i915_refct_sgt_ops *ops)
> > +{
> > +       kref_init(&rsgt->kref);
> > +       rsgt->table.sgl = NULL;
> > +       rsgt->size = size;
> > +       rsgt->ops = ops;
> > +}
>
> Could maybe make this __i915_refct_sgt_init(), since it inits more
> than
> just the ops?
>
>

Will change.

Thanks,
Thomas