linux-kernel - Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs

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Message-ID: <2a24ae2a-e2f3-52b2-0763-2ce31ba18965@alibaba-inc.com>
Date:   Tue, 10 Oct 2017 02:53:18 +0800
From:   "Yang Shi" <yang.s@...baba-inc.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when
 unreclaimable slabs > user memory



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@...e.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

>