Re: [RFC] kbuild: bpf: Do not run pahole with -j on 32bit userspace

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Mon, Aug 26, 2024 at 10:57:22AM +0200, Jiri Slaby wrote:
> On 22. 08. 24, 17:24, Arnaldo Carvalho de Melo wrote:
> > On Thu, Aug 22, 2024 at 11:55:05AM +0800, Shung-Hsi Yu wrote:
> > I stumbled on this limitation as well when trying to build the kernel on
> > a Libre Computer rk3399-pc board with only 4GiB of RAM, there I just
> > created a swapfile and it managed to proceed, a bit slowly, but worked
> > as well.
> 
> Here, it hits the VM space limit (3 G).

right, in my case it was on a 64-bit system, so just not enough memory,
not address space.
 
> > Please let me know if what is in the 'next' branch of:

> > https://git.kernel.org/pub/scm/devel/pahole/pahole.git

> > Works for you, that will be extra motivation to move it to the master
> > branch and cut 1.28.

> on 64bit (-j1):
> * master: 3.706 GB
> (* master + my changes: 3.559 GB)
> * next: 3.157 GB
 
> on 32bit:
>  * master-j1: 2.445 GB
>  * master-j16: 2.608 GB
>  * master-j32: 2.811 GB
>  * next-j1: 2.256 GB
>  * next-j16: 2.401 GB
>  * next-j32: 2.613 GB
> 
> It's definitely better. So I think it could work now, if the thread count
> was limited to 1 on 32bit. As building with -j10, -j20 randomly fails on
> random machines (32bit processes only of course). Unlike -j1.

Cool, I just merged a patch from Alan Maguire that should help with the
parallel case, would be able to test it? It is in the 'next' branch:

⬢[acme@toolbox pahole]$ git log --oneline -5
f37212d1611673a2 (HEAD -> master) pahole: Teduce memory usage by smarter deleting of CUs

Excerpt of the above:

    This leads to deleting ~90 CUs during parallel vmlinux BTF generation
    versus deleting just 1 prior to this change.

c7ec9200caa7d485 btf_encoder: Add "distilled_base" BTF feature to split BTF generation
bc4e6a9adfc72758 pahole: Sync with libbpf-1.5
5e3ed3ec2947c69f pahole: Do --lang_exclude CU filtering earlier
c46455bb0379fa38 dwarf_loader: Allow filtering CUs early in loading
⬢[acme@toolbox pahole]$

- Arnaldo