[RFC PATCH 02/18] drm/ttm: Add per-BO eviction tracking

[Matthew Brost]

On Thu, Apr 25, 2024 at 08:18:38AM +0200, Christian König wrote:
> Am 24.04.24 um 18:56 schrieb Friedrich Vock:
> > Make each buffer object aware of whether it has been evicted or not.
> 
> That reverts some changes we made a couple of years ago.
> 
> In general the idea is that eviction isn't something we need to reverse in
> TTM.
> 
> Rather the driver gives the desired placement.
> 
> Regards,
> Christian.
> 

We have added a concept similar to this in drm_gpuvm [1]. GPUVM
maintains a list of evicted BOs and when the GPUVM is locked for
submission it has validate vfunc which is called on each BO. If driver
is using TTM, this is where the driver would call TTM BO validate which
unevicts the BO. Well at least this what we do it Xe [2].

The uneviction is a per VM operation not a global one. With this, a
global eviction list does not seem correct (admittedly not through the
entire series).

Matt

[1] https://elixir.bootlin.com/linux/v6.8.7/source/drivers/gpu/drm/drm_gpuvm.c#L86
[2] https://elixir.bootlin.com/linux/v6.8.7/source/drivers/gpu/drm/xe/xe_vm.c#L464

> > 
> > Signed-off-by: Friedrich Vock <friedrich.vock at gmx.de>
> > ---
> >   drivers/gpu/drm/ttm/ttm_bo.c |  1 +
> >   include/drm/ttm/ttm_bo.h     | 11 +++++++++++
> >   2 files changed, 12 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> > index edf10618fe2b2..3968b17453569 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> > @@ -980,6 +980,7 @@ int ttm_bo_init_reserved(struct ttm_device *bdev, struct ttm_buffer_object *bo,
> >   	bo->pin_count = 0;
> >   	bo->sg = sg;
> >   	bo->bulk_move = NULL;
> > +	bo->evicted_type = TTM_NUM_MEM_TYPES;
> >   	if (resv)
> >   		bo->base.resv = resv;
> >   	else
> > diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
> > index 0223a41a64b24..8a1a29c6fbc50 100644
> > --- a/include/drm/ttm/ttm_bo.h
> > +++ b/include/drm/ttm/ttm_bo.h
> > @@ -121,6 +121,17 @@ struct ttm_buffer_object {
> >   	unsigned priority;
> >   	unsigned pin_count;
> > 
> > +	/**
> > +	 * @evicted_type: Memory type this BO was evicted from, if any.
> > +	 * TTM_NUM_MEM_TYPES if this BO was not evicted.
> > +	 */
> > +	int evicted_type;
> > +	/**
> > +	 * @evicted: Entry in the evicted list for the resource manager
> > +	 * this BO was evicted from.
> > +	 */
> > +	struct list_head evicted;
> > +
> >   	/**
> >   	 * @delayed_delete: Work item used when we can't delete the BO
> >   	 * immediately
> > --
> > 2.44.0
> > 
>