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

["Yang Shi" <yang.s@alibaba-inc.com>]

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@suse.com>
> 
> [1] http://lkml.kernel.org/r/1507492085-42264-1-git-send-email-yang.s@alibaba-inc.com

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

> 

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