Slub: Increased mem consumption on cpu,mem-less node powerpc guest

[Vlastimil Babka]

On 3/17/20 5:25 PM, Srikar Dronamraju wrote:
> * Vlastimil Babka <vbabka at suse.cz> [2020-03-17 16:56:04]:
> 
>> 
>> I wonder why do you get a memory leak while Sachin in the same situation [1]
>> gets a crash? I don't understand anything anymore.
> 
> Sachin was testing on linux-next which has Kirill's patch which modifies
> slub to use kmalloc_node instead of kmalloc. While Bharata is testing on
> upstream, which doesn't have this. 

Yes, that Kirill's patch was about the memcg shrinker map allocation. But the
patch hunk that Bharata posted as a "hack" that fixes the problem, it follows
that there has to be something else that calls kmalloc_node(node) where node is
one that doesn't have present pages.

He mentions alloc_fair_sched_group() which has:

        for_each_possible_cpu(i) {
                cfs_rq = kzalloc_node(sizeof(struct cfs_rq),
                                      GFP_KERNEL, cpu_to_node(i));
...
                se = kzalloc_node(sizeof(struct sched_entity),
                                  GFP_KERNEL, cpu_to_node(i));

I assume one of these structs is 1k and other 512 bytes (rounded) and that for
some possible cpu's cpu_to_node(i) will be 0, which has no present pages. And as
Bharata pasted, node_to_mem_node(0) = 0
So this looks like the same scenario, but it doesn't crash? Is the node 0
actually online here, and/or does it have N_NORMAL_MEMORY state?

>> 
>> [1]
>> https://lore.kernel.org/linux-next/3381CD91-AB3D-4773-BA04-E7A072A63968@linux.vnet.ibm.com/
>> 
>