Your message dated Fri, 23 Oct 2026 06:49:50 +0200
with message-id <[email protected]>
and subject line Re: Bug#1149923: vtk9: Please consider reducing --require-mem
for guess_concurrency to 3.8G
has caused the Debian Bug report #1149923,
regarding vtk9: Please revert the usage of guess_concurrency
to be marked as done.
This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.
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1149923: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1149923
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--- Begin Message ---
Source: vtk9
Version: 9.6.2+ds-1
Severity: normal
Hi,
Starting with vtk9 9.6.2+ds-1, the package use guess-concurrency to
limit parallel workers, which is a good move. However on some build
daemons, it significantly increased the build time.
One of the reason is bug#1149922. The other reason is that hardware or
VMs usually use an integer number of GiB for the RAM (and often a power
of 2). There is always a bit of RAM lost (kernel code or data, reserved
memory, ...) and this is enough to get just below the 4G per core.
Would you consider reducing the required memory to 3.8G (guess-concurrency
accepts
floating numbers) to account for that?
Thanks
Aurelien
--- End Message ---
--- Begin Message ---
Hi,
On 2026-10-12 23:35, Maximiliano Curia wrote:
> ¡Hola Adrian!
>
> El 2026-10-11 a las 17:26 +0300, Adrian Bunk escribió:
> > I'm raising the severity to serious:
> > This change has increased the build time on the slower riscv64 buildds
> > from 4 days to 6 days, it has to be reverted.
>
> I wasn't aware that a build taking longer than before is an RC bug, but
> I agree that we should work on this issue and fix it as soon as
> possible.
>
> > Given the near-perfect scaling of a 2.76x build time increase on the
> > same i386 buildd where this guess-concurrency use reduced the number of
> > cores used by a factor of 3, even 2G would likely still harm build time
> > on some architectures.
> >
> > It is harmful to use guess-concurrency unless:
> > 1. it is fixing an actual problem that has been observed, and
> > 2. the numbers have been properly measured and not just guessed
>
> I only added guess-concurrency after running into OOM issues over and
> over while working on the vtk9 package. This happened both on my local
> machine and on the debusine builders I was using to test, because in
> both cases there were a high number of processors and not as much memory
> as the build required (in my case it was 16 processors and 64 GB of
> RAM).
>
> So, it is indeed fixing an actual problem.
>
> You can see that the package that was uploaded to experimental didn't
> manage to build on riscv64 and it's almost certainly for this reason
> (when the build dies due to OOM there are no logs left behind to
> actually verify this).
>
> Now, regarding the measuring, it's true that in the package I uploaded
> to unstable I had added a ballpark estimation and that I didn't take
> into account that it would be a very different number for 32bits. I have
> now taken a much more accurate measure and I've found that:
>
> - In 64bit architectures, the maximum amount of memory that a single
> process takes is slightly over 6 GB. - In 64bit architectures, the
> time-weighted average amount of memory is 1 GB.
> - In 32bit architectures, the maximum amount of memory is slightly over 2 GB
> - In 32bit architectures, the time-weighted average amount of memory is 550
> MB.
> - In both cases, the memory consumption is quite skewed, some processes
> take very little memory and very little CPU time, while others take a
> lot of memory and time.
>
Thanks for doing that. The above changes combined to the fix done on the
guess-concurrency side (#1149922), 4 jobs are used again on the riscv64
build daemons. There is still less jobs than before used on amd64 and
i386, but the resulting build time is comparable.
I am therefore closing the bug.
Regards
Aurelien
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
[email protected] http://aurel32.net
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