Re: [PATCH 3/4] drm/i915: allow volatile buffers to use ttm pool allocator

[Robert Beckett]

On 11/05/2022 13:42, Thomas Hellström wrote:
> Hi, Bob,
>
> On Tue, 2022-05-03 at 19:13 +0000, Robert Beckett wrote:
> > internal buffers should be shmem backed.
> > if a volatile buffer is requested, allow ttm to use the pool
> > allocator
> > to provide volatile pages as backing
> >
> > Signed-off-by: Robert Beckett <bob.beckett@xxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > index 4c25d9b2f138..fdb3a1c18cb6 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > @@ -309,7 +309,8 @@ static struct ttm_tt *i915_ttm_tt_create(struct
> > ttm_buffer_object *bo,
> >                  page_flags |= TTM_TT_FLAG_ZERO_ALLOC;
> >   
> >          caching = i915_ttm_select_tt_caching(obj);
> > -       if (i915_gem_object_is_shrinkable(obj) && caching ==
> > ttm_cached) {
> > +       if (i915_gem_object_is_shrinkable(obj) && caching ==
> > ttm_cached &&
> > +           !i915_gem_object_is_volatile(obj)) {
> >                  page_flags |= TTM_TT_FLAG_EXTERNAL |
> >                                TTM_TT_FLAG_EXTERNAL_MAPPABLE;
> >                  i915_tt->is_shmem = true;
>
> While this is ok, I think it also needs adjustment in the i915_ttm
> shrink callback. If someone creates a volatile smem object which then
> hits the shrinker, I think we might hit asserts that it's a is_shem
> ttm?
>
> In this case, the shrink callback should just i915_ttm_purge().

agreed. nice catch.
I'll fix for v2

looks like we could maybe do with some extra shrinker testing too? looks 
like nothing caught this during CI testing

> /Thomas