linux-kernel - Re: [PATCH v2] kmemleak: survive in a low-memory situation

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Date:   Mon, 7 Jan 2019 21:06:37 -0500
From:   Qian Cai <cai@....pw>
To:     Catalin Marinas <catalin.marinas@....com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     akpm@...ux-foundation.org, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kmemleak: survive in a low-memory situation



On 1/7/19 5:43 AM, Catalin Marinas wrote:
> On Thu, Jan 03, 2019 at 06:07:35PM +0100, Michal Hocko wrote:
>>>> On Wed 02-01-19 13:06:19, Qian Cai wrote:
>>>> [...]
>>>>> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
>>>>> index f9d9dc250428..9e1aa3b7df75 100644
>>>>> --- a/mm/kmemleak.c
>>>>> +++ b/mm/kmemleak.c
>>>>> @@ -576,6 +576,16 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
>>>>>  	struct rb_node **link, *rb_parent;
>>>>>  
>>>>>  	object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp));
>>>>> +#ifdef CONFIG_PREEMPT_COUNT
>>>>> +	if (!object) {
>>>>> +		/* last-ditch effort in a low-memory situation */
>>>>> +		if (irqs_disabled() || is_idle_task(current) || in_atomic())
>>>>> +			gfp = GFP_ATOMIC;
>>>>> +		else
>>>>> +			gfp = gfp_kmemleak_mask(gfp) | __GFP_DIRECT_RECLAIM;
>>>>> +		object = kmem_cache_alloc(object_cache, gfp);
>>>>> +	}
>>>>> +#endif
> [...]
>> I will not object to this workaround but I strongly believe that
>> kmemleak should rethink the metadata allocation strategy to be really
>> robust.
> 
> This would be nice indeed and it was discussed last year. I just haven't
> got around to trying anything yet:
> 
> https://marc.info/?l=linux-mm&m=152812489819532
> 

It could be helpful to apply this 10-line patch first if has no fundamental
issue, as it survives probably 50 times running LTP oom* workloads without a
single kmemleak allocation failure.

Of course, if someone is going to embed kmemleak metadata into slab objects
itself soon, this workaround is not needed.