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increase kernel.pid_max?

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  increase kernel.pid_max? Harald Dunkel <harri@afaics.de> - 2020-02-29 20:20 +0100
    Re: increase kernel.pid_max? Ian Campbell <ijc@debian.org> - 2020-03-01 02:50 +0100
      Re: increase kernel.pid_max? Ben Hutchings <ben@decadent.org.uk> - 2020-03-01 18:00 +0100
        Re: increase kernel.pid_max? Ian Campbell <ijc@debian.org> - 2020-03-02 00:20 +0100
        Re: increase kernel.pid_max? Harald Dunkel <harri@afaics.de> - 2020-04-12 17:50 +0200

#66431 — increase kernel.pid_max?

Hi folks,

looking at the number of cores and highly parallel applications
I wonder if it would be reasonable to increase the default
kernel.pid_max (currently 0x8000) to lets say 0x3fffff?

Do you expect negative side effects?


Regards
Harri

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#66435

On Sat, 2020-02-29 at 20:14 +0100, Harald Dunkel wrote:
> Hi folks,
> 
> looking at the number of cores and highly parallel applications
> I wonder if it would be reasonable to increase the default
> kernel.pid_max (currently 0x8000) to lets say 0x3fffff?
> 
> Do you expect negative side effects?

It's already 0x400000 on my machine and everything is fine. I haven't
(knowingly) tweaked anything so I guess this is the default on recent
machines, this laptop is running 5.4.0-3-amd64 (testing userspace,
although not updated for a little bit).

I can't actually find when/where this changed in recent history -- I've
only noticed these large pids in recent months, but it's entirely
possible I'm simply not that observant.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=72680a191b934377430032f93af15ef50aafb3a8 was in 2010 and a 2.6.x
kernel.

Ian.

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#66436

[Multipart message — attachments visible in raw view] — view raw

On Sun, 2020-03-01 at 09:24 +0800, Ian Campbell wrote:
> On Sat, 2020-02-29 at 20:14 +0100, Harald Dunkel wrote:
> > Hi folks,
> > 
> > looking at the number of cores and highly parallel applications
> > I wonder if it would be reasonable to increase the default
> > kernel.pid_max (currently 0x8000) to lets say 0x3fffff?
> > 
> > Do you expect negative side effects?
> 
> It's already 0x400000 on my machine and everything is fine. I haven't
> (knowingly) tweaked anything so I guess this is the default on recent
> machines, this laptop is running 5.4.0-3-amd64 (testing userspace,
> although not updated for a little bit).
> 
> I can't actually find when/where this changed in recent history -- I've
> only noticed these large pids in recent months, but it's entirely
> possible I'm simply not that observant.

This was a change in systemd 243:

        * On 64 bit systems, the "kernel.pid_max" sysctl is now bumped to
          4194304 by default, i.e. the full 22bit range the kernel allows, up
          from the old 16bit range.

Ben.

> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=72680a191b934377430032f93af15ef50aafb3a8 was in 2010 and a 2.6.x
> kernel.
> 
> Ian.
> 
-- 
Ben Hutchings
It is a miracle that curiosity survives formal education.
                                                      - Albert Einstein

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#66437

On Sun, 2020-03-01 at 16:53 +0000, Ben Hutchings wrote:
> On Sun, 2020-03-01 at 09:24 +0800, Ian Campbell wrote:
> > I can't actually find when/where this changed in recent history -- I've
> > only noticed these large pids in recent months, but it's entirely
> > possible I'm simply not that observant.
> 
> This was a change in systemd 243:

Thanks, that's one of the few places I didn't think to look!

Ian.

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#66735

Would it be reasonable to configure these kind of items and
limits *independent* of the init system? This would help to
avoid unexpected side effects of changing the init system.


Thanx in advance
Harri

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