linux-kernel - Re: [PATCH] fix linux kernel BTF builds: increase max percpu variables by 10x

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Date: Fri, 1 Mar 2024 10:32:34 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Alan Maguire <alan.maguire@...cle.com>,
 Arnaldo Carvalho de Melo <acme@...hat.com>,
 Alexei Starovoitov <ast@...nel.org>, bpf@...r.kernel.org,
 LKML <linux-kernel@...r.kernel.org>, dwarves@...r.kernel.org,
 Suren Baghdasaryan <surenb@...gle.com>,
 Kent Overstreet <kent.overstreet@...ux.dev>
Subject: Re: [PATCH] fix linux kernel BTF builds: increase max percpu
 variables by 10x

On 3/1/24 06:14, Jiri Olsa wrote:
> On Thu, Feb 29, 2024 at 10:15:23AM -0800, John Hubbard wrote:
>>> ...
>>> Running
>>>
>>> bpftool btf dump file vmlinux |grep "] VAR"
>>>
>>
>> $ bpftool btf dump file vmlinux |grep "] VAR" | wc -l
>> 4852
>>
>> $ bpftool btf dump file vmlinux |grep "] VAR" | tail -5
>> [136994] VAR '_alloc_tag_cntr.9' type_id=703, linkage=static
>> [137003] VAR '_alloc_tag_cntr.5' type_id=703, linkage=static
>> [137004] VAR '_alloc_tag_cntr.7' type_id=703, linkage=static
>> [137005] VAR '_alloc_tag_cntr.17' type_id=703, linkage=static
>> [137018] VAR '_alloc_tag_cntr.14' type_id=703, linkage=static
>>
>>> ...should give us a sense of what's going on. I only see 375 per-cpu
>>> variables when I do this so maybe there's something
>>> kernel-config-specific that might explain why you have so many more?
>>
>> Yes, as mentioned earlier, this is specifically due to the .config.
>> The .config is a huge distro configuration that has a lot of modules
>> enabled.
> 
> could you share your .config? I tried with fedora .config and got 396
> per cpu variables, I wonder where this is coming from
> 

Attaching it. And based on your results, I think that Suren's Memory
allocation profiling patchset v4 [1] may also be required, as that is what
I was building.

Cc: Suren and Kent. btw, I the whole reason I went down this path was that
I recommended your patchset in order to zero in on a memory leak that a
colleague is debugging. This patchset provides a new view of allocations
and leaks and we have high hopes for it. :)


[1] https://lore.kernel.org/20240221194052.927623-1-surenb@google.com


thanks,
-- 
John Hubbard
NVIDIA

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