On Thu 20-06-19 07:44:27, Shakeel Butt wrote: > On Wed, Jun 19, 2019 at 10:50 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > On Wed 19-06-19 16:25:14, Shakeel Butt wrote: > > > Currently for CONFIG_SLUB, if a memcg kmem cache creation is failed and > > > the corresponding root kmem cache has SLAB_PANIC flag, the kernel will > > > be crashed. This is unnecessary as the kernel can handle the creation > > > failures of memcg kmem caches. > > > > AFAICS it will handle those by simply not accounting those objects > > right? > > > > The memcg kmem cache creation is async. The allocation has already > been decided not to be accounted on creation trigger. If memcg kmem > cache creation is failed, it will fail silently and the next > allocation will trigger the creation process again. Ohh, right I forgot that it will get retried. This would be useful to mention in the changelog as it is not straightforward from reading just the particular function. > > > Additionally CONFIG_SLAB does not > > > implement this behavior. So, to keep the behavior consistent between > > > SLAB and SLUB, removing the panic for memcg kmem cache creation > > > failures. The root kmem cache creation failure for SLAB_PANIC correctly > > > panics for both SLAB and SLUB. > > > > I do agree that panicing is really dubious especially because it opens > > doors to shut the system down from a restricted environment. So the > > patch makes sesne to me. > > > > I am wondering whether SLAB_PANIC makes sense in general though. Why is > > it any different from any other essential early allocations? We tend to > > not care about allocation failures for those on bases that the system > > must be in a broken state to fail that early already. Do you think it is > > time to remove SLAB_PANIC altogether? > > > > That would need some investigation into the history of SLAB_PANIC. I > will look into it. Well, I strongly suspect this is a relict from the past. I have hard time to believe that the system would get to a usable state if many of those caches would fail to allocate. And as Dave said in his reply it is quite silly to give this weapon to a random driver hands. Everybody just thinks his toy is the most important one... -- Michal Hocko SUSE Labs
