On Thu 21-12-17 00:20:44, Aliaksei Karaliou wrote: > > > On 12/20/2017 02:57 PM, Michal Hocko wrote: > > 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. > > Regarding the other locations where return code is ignored, I think I will > try to fix them as I did in Lustre code recently. That would be really appreciated! > However, it might be not straightforward and zsmalloc is good example - > we understand that failure is not critical and we can live without shrinker. > > Locations specified by Michal are also different, for example: > > drivers/gpu/drm/i915/i915_gem_shrinker.c:508: WARN_ON(register_shrinker(&i915->mm.shrinker)); > - this change is intentional. I would be careful here. I believe that the WARN_ON is not a solution here. i915 can allocated _a lot_ of memory IIRC so a missing shrinker can be really problematic. Talk to i915 people. > arch/x86/kvm/mmu.c:5485: register_shrinker(&mmu_shrinker); > - was made before register_shrinker() became non-void. Yes this would be the case for the most shrinkers. Glauber simply didn't bother to handle those because failing registration is basically impossible. > and so on. The question is what to do in each particular case ? Bail out unless the shrinker is along the zsmalloc case. > Some people may consider wrapping it with WARN_ON to be rather good option too > while the others will prefer to consider it as a critical failure or at least > do their own logging, with still looks similar with WARN_ON for me imho. Talk to respective maintainers and they will give hints. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
