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To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
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        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jann Horn <jannh@google.com>
References: <20210524233946.20352-1-vbabka@suse.cz>
 <20210524233946.20352-3-vbabka@suse.cz>
 <20210525101742.GK30378@techsingularity.net>
From:   Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [RFC 02/26] mm, slub: allocate private object map for
 validate_slab_cache()
Message-ID: <aad15d62-23c0-9eeb-d61f-a214eb57fb19@suse.cz>
Date:   Tue, 25 May 2021 12:36:52 +0200
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On 5/25/21 12:17 PM, Mel Gorman wrote:
> On Tue, May 25, 2021 at 01:39:22AM +0200, Vlastimil Babka wrote:
>> validate_slab_cache() is called either to handle a sysfs write, or from a
>> self-test context. In both situations it's straightforward to preallocate a
>> private object bitmap instead of grabbing the shared static one meant for
>> critical sections, so let's do that.
>> 
>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
>>
>> <SNIP>
>>
>> @@ -4685,10 +4685,17 @@ static long validate_slab_cache(struct kmem_cache *s)
>>  	int node;
>>  	unsigned long count = 0;
>>  	struct kmem_cache_node *n;
>> +	unsigned long *obj_map;
>> +
>> +	obj_map = bitmap_alloc(oo_objects(s->oo), GFP_KERNEL);
>> +	if (!obj_map)
>> +		return -ENOMEM;
>>  
> 
> 
> Most callers of validate_slab_cache don't care about the return value
> except when the validate sysfs file is written. Should a simply
> informational message be displayed for -ENOMEM in case a writer to
> validate fails and it's not obvious it was because of an allocation
> failure?

he other callers are all in the effectively dead resiliency_test() code, which
has meanwhile been replaced in mmotm by kunit tests meanwhile. But it's true
those don't check the results either for now.

> It's a fairly minor concern so whether you add a message or not

I think I'll rather fix up the tests. Or do you mean that -ENOMEM for a sysfs
write is also not enough and there should be a dmesg explanation for that case?

> Acked-by: Mel Gorman <mgorman@techsingularity.net>

Thanks!