[PATCH 1/3] drm/etnaviv: don't trigger OOM killer when page allocation fails

[Michal Hocko]

On Tue 20-06-17 11:25:24, Daniel Vetter wrote:
> On Tue, Jun 20, 2017 at 11:22:06AM +0200, Lucas Stach wrote:
> > Am Dienstag, den 20.06.2017, 11:06 +0200 schrieb Daniel Vetter:
> > > On Tue, Jun 06, 2017 at 09:17:06AM +0200, Lucas Stach wrote:
> > > > GPU buffers can be quite large, so userspace is expected to deal with
> > > > allocation failure. Don't trigger the OOM killer when page allocation for
> > > > the GEM objects fails, as this opens an easy possiblity for unprivileged
> > > > applications to DOS the system,a s the shmem pages are not fully accounted
> > > > to the allocating process.
> > > > 
> > > > Signed-off-by: Lucas Stach <dev at lynxeye.de>
> > > > ---
> > > >  drivers/gpu/drm/etnaviv/etnaviv_gem.c | 3 ++-
> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > > > index f0efc5d..4c53508 100644
> > > > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > > > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > > > @@ -662,7 +662,8 @@ static struct drm_gem_object *__etnaviv_gem_new(struct drm_device *dev,
> > > >  		 * going to pin these pages.
> > > >  		 */
> > > >  		mapping = obj->filp->f_mapping;
> > > > -		mapping_set_gfp_mask(mapping, GFP_HIGHUSER);
> > > > +		mapping_set_gfp_mask(mapping, GFP_HIGHUSER |
> > > > +				     __GFP_NORETRY | __GFP_NOWARN);
> > > 
> > > _NORETRY means the mm does try hard at all to free memory. We've just done
> > > this patch in 4.12 and totally regret it, because now gpu tasks run out of
> > > memory with plenty of (gpu) memory available that could be reaped.
> > > 
> > > There's some discussions going on with Michal Hocko and Chris Wilson
> > > about possible solutions for this without so much hacks.
> > 
> > Thanks for the heads up. In contrast to some of the other drivers
> > Etnaviv hasn't grown a proper shrinker yet, so I still think this patch
> > is a step in the right direction for the time being.
> > Currently with Etnaviv sitting on lots of GPU memory and the MM trying
> > hard to free more memory for GPU usage a simple piglit run might
> > pressure the OOM killer hard enough to bring the system down by killing
> > PID 1.
> 
> Ah ok, that changes the balance of course. Time to type that shrinker I'd
> say :-)

Yeah, shrinker sounds like an absolute must. Anyway, I've posted
__GFP_RETRY_MAYFAIL patchset [1] so you can use that flag.

[1] http://lkml.kernel.org/r/20170623085345.11304-1-mhocko@kernel.org
-- 
Michal Hocko
SUSE Labs