Re: [PATCH 2/3] mm: oom: show unreclaimable slab info when kernel panic

[Michal Hocko]

On Thu 28-09-17 01:25:50, Yang Shi wrote:
> 
> 
> On 9/27/17 3:45 AM, Michal Hocko wrote:
> > On Wed 27-09-17 08:53:35, Yang Shi wrote:
> > > Kernel may panic when oom happens without killable process sometimes it
> > > is caused by huge unreclaimable slabs used by kernel.
> > > 
> > > Although kdump could help debug such problem, however, kdump is not
> > > available on all architectures and it might be malfunction sometime.
> > > And, since kernel already panic it is worthy capturing such information
> > > in dmesg to aid touble shooting.
> > > 
> > > Print out unreclaimable slab info (used size and total size) which
> > > actual memory usage is not zero (num_objs * size != 0) when:
> > >    - unreclaimable slabs : all user memory > unreclaim_slabs_oom_ratio
> > >    - panic_on_oom is set or no killable process
> > 
> > OK, this is better but I do not see why this should be tunable via proc.
> 
> Just thought someone might want to dump unreclaimable slab info
> unconditionally.

If that ever happens then we will eventually add it. But do not add proc
knobs for theoretical usecases. We will have to maintain them and it
can turn into a maint. pain. Like some others in the past.
-- 
Michal Hocko
SUSE Labs