Re: [PATCH bpf-next v6 1/1] bpf, docs: document BPF_MAP_TYPE_ARRAY

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Daniel Borkmann <daniel@xxxxxxxxxxxxx> writes:

> On 10/6/22 1:36 PM, Jiri Olsa wrote:
>> I recently hit 32k size limit for per-cpu map value.. it seems to be
>> size limit for generic per cpu allocation, but would be great to have
>> it confirmed by somebody who knows mm better ;-)
>
> Yes, for percpu the max is PCPU_MIN_UNIT_SIZE which is 32k, see mm/percpu.c +1756.
> In many cases it's implementation specific, so it probably does not make too much
> sense to state limits like 2^32, or at least it should say that its theoretical/uapi
> limit and actual limits may be implementation/config specific.

Yes, good point. I will just drop the 2^32 bit. Same issue was
raised by Stanislav Fomichev for BPF_MAP_TYPE_HASH here:

https://patchwork.kernel.org/project/netdevbpf/patch/20220713211612.84782-1-donald.hunter@xxxxxxxxx/#24936386



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