Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory

[Yang Shi]

On 10/8/17 11:36 PM, Michal Hocko wrote:
> On Mon 09-10-17 08:33:16, Michal Hocko wrote:
> > On Sat 07-10-17 00:37:55, Yang Shi wrote:
> > > On 10/6/17 2:37 AM, Michal Hocko wrote:
> > > > On Thu 05-10-17 05:29:10, Yang Shi wrote:
> > [...]
> > > > > +	list_for_each_entry_safe(s, s2, &slab_caches, list) {
> > > > > +		if (!is_root_cache(s) || (s->flags & SLAB_RECLAIM_ACCOUNT))
> > > > > +			continue;
> > > > > +
> > > > > +		memset(&sinfo, 0, sizeof(sinfo));
> > > >
> > > > why do you zero out the structure. All the fields you are printing are
> > > > filled out in get_slabinfo.
> > >
> > > No special reason, just wipe out the potential stale data on the stack.
> >
> > Do not add code that has no meaning. The OOM killer is a slow path but
> > that doesn't mean we should throw spare cycles out of the window.
>
> With this fixed and the compile fix [1] folded, feel free to add my
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>
> [1] http://lkml.kernel.org/r/1507492085-42264-1-git-send-email-yang.s@xxxxxxxxxxxxxxx

Did some more thorough test and took the code a little deeper, it sounds 
!CONFIG_SLOB is not enough. Some data structure and functions depends on 
CONFIG_SLUB_DEBUG, i.e. kmem_cache_node->total_objects and 
node_nr_objs(), which are essential of get_slabinfo().

So, I'm supposed it makes more sense to protect the related slab stats 
code and the unreclaimable slabinfo dump with CONFIG_SLAB || 
CONFIG_SLUB_DEBUG.

Thanks,
Yang

>