* Vlastimil Babka <vbabka@xxxxxxx> [2020-03-17 17:45:15]:
> On 3/17/20 5:25 PM, Srikar Dronamraju wrote:
> > * Vlastimil Babka <vbabka@xxxxxxx> [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));
>
Sachin's experiment.
Upstream-next/ memcg /
possible nodes were 0-31
online nodes were 0-1
kmalloc_node called for_each_node / for_each_possible_node.
This would crash while allocating slab from !N_ONLINE nodes.
Bharata's experiment.
Upstream
possible nodes were 0-1
online nodes were 0-1
kmalloc_node called for_each_online_node/ for_each_possible_cpu
i.e kmalloc is called for N_ONLINE nodes.
So wouldn't crash
Even if his possible nodes were 0-256. I don't think we have kmalloc_node
being called in !N_ONLINE nodes. Hence its not crashing.
If we see the above code that you quote, kzalloc_node is using cpu_to_node
which in Bharata's case will always return 1.
> 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?
I still dont have any clue on the leak though.
--
Thanks and Regards
Srikar Dronamraju
