Re: [PATCH v2 2/2] drm/msm/gem: Add modparam to disable shrinker blocking

[Rob Clark]

On Mon, Sep 14, 2026 at 12:56 AM Konrad Dybcio
<konrad.dybcio@xxxxxxxxxxxxxxxx> wrote:
>
> On 9/12/26 4:59 PM, Rob Clark wrote:
> > Normally if we are under enough memory pressure, the shrinker will
> > eventually start waiting for BOs to become idle.  In some very latency
> > sensitive use-cases this is undesirable.
> >
> > Signed-off-by: Rob Clark <robin.clark@xxxxxxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/msm/msm_gem_shrinker.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> > index 3514d5c84989..83ee032cb21d 100644
> > --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
> > +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> > @@ -19,6 +19,10 @@ static bool enable_eviction = true;
> >  MODULE_PARM_DESC(enable_eviction, "Enable swappable GEM buffers");
> >  module_param(enable_eviction, bool, 0600);
> >
> > +static bool eviction_can_block = true;
> > +MODULE_PARM_DESC(eviction_can_block, "Enable blocking for GEM buffer to become idle for eviction");
> > +module_param(eviction_can_block, bool, 0600);
> > +
> >  static bool can_swap(void)
> >  {
> >       return enable_eviction && get_nr_swap_pages() > 0;
> > @@ -26,6 +30,8 @@ static bool can_swap(void)
> >
> >  static bool can_block(struct shrink_control *sc)
> >  {
> > +     if (!eviction_can_block)
> > +             return false;
> >       return (sc->gfp_mask & __GFP_DIRECT_RECLAIM) ||
> >              (current_is_kswapd() && (sc->gfp_mask & __GFP_KSWAPD_RECLAIM));
> >  }
>
> This is just a guess, but can we always keep both and jump out
> of msm_gem_shrinker_scan() early if we can satistfy nr_to_scan
> without locking?

We do this already.  But a pure vulkan/VM_BIND userspace that happens
to have realtime compositor requirements (vr) has a hard time under
heavy memory pressure.  Without BO tracking the kernel ends up quickly
looking for anything to evict and not necessarily making good choices.
I have some half baked ideas.. tracking LRU vm might help, etc.

BR,
-R