Re: [PATCH v2] mm/zsmalloc: simplify shrinker init/destroy

[Michal Hocko <mhocko@kernel.org>]

On Wed 20-12-17 12:38:35, Michal Hocko wrote:
> On Wed 20-12-17 20:05:35, Tetsuo Handa wrote:
> > On 2017/12/20 18:25, Michal Hocko wrote:
> > > On Wed 20-12-17 18:16:53, Sergey Senozhatsky wrote:
> > >> On (12/20/17 10:08), Michal Hocko wrote:
> > >> [..]
> > >>>> let's keep void zs_register_shrinker() and just suppress the
> > >>>> register_shrinker() must_check warning.
> > >>>
> > >>> I would just hope we simply drop the must_check nonsense.
> > >>
> > >> agreed. given that unregister_shrinker() does not oops anymore,
> > >> enforcing that check does not make that much sense.
> > > 
> > > Well, the registration failure is a failure like any others. Ignoring
> > > the failure can have bad influence on the overal system behavior but
> > > that is no different from thousands of other functions. must_check is an
> > > overreaction here IMHO.
> > > 
> > 
> > I don't think that must_check is an overreaction.
> > As of linux-next-20171218, no patch is available for 10 locations.
> > 
> > drivers/staging/android/ion/ion_heap.c:306:     register_shrinker(&heap->shrinker);
> > drivers/staging/android/ashmem.c:857:   register_shrinker(&ashmem_shrinker);
> > drivers/gpu/drm/ttm/ttm_page_alloc_dma.c:1185:  register_shrinker(&manager->mm_shrink);
> > drivers/gpu/drm/ttm/ttm_page_alloc.c:484:       register_shrinker(&manager->mm_shrink);
> > drivers/gpu/drm/i915/i915_gem_shrinker.c:508:   WARN_ON(register_shrinker(&i915->mm.shrinker));
> > drivers/gpu/drm/msm/msm_gem_shrinker.c:154:     WARN_ON(register_shrinker(&priv->shrinker));
> > drivers/md/dm-bufio.c:1756:     register_shrinker(&c->shrinker);
> > drivers/android/binder_alloc.c:1012:    register_shrinker(&binder_shrinker);
> > arch/x86/kvm/mmu.c:5485:        register_shrinker(&mmu_shrinker);
> > fs/xfs/xfs_qm.c:698:    register_shrinker(&qinf->qi_shrinker);
> 
> And how exactly has the must_check helped for those? Come on, start
> being serious finally. This is a matter of fixing those. You have done
> a good deal of work for some, it just takes to finish the rest. The
> warning doesn't help on its own, it just makes people ignore it after
> some time or make it silent in some way.

Also have a look at how WARN_ON simply papers over the wrong code and
must_check will not help you the slightest.
-- 
Michal Hocko
SUSE Labs

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