[Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Dimitri John Ledkov]

** Also affects: procps (Ubuntu)
   Importance: Undecided
   Status: New

** Changed in: procps (Ubuntu)
   Status: New => Fix Released

** Changed in: linux (Ubuntu)
   Status: Incomplete => Invalid

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Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Invalid
Status in procps package in Ubuntu:
  Fix Released

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

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[Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Viktor Mihajlovski]

In my opinion it will be best to set vm.allocate_pgste = 1
unconditionally, regardless of whether qemu is installed or not, and
only have the user switch it off for certain memory-intensive workloads
(if required at all).

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Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

To manage notifications about this bug go to:
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[Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Christian Borntraeger]

My modprobe.conf solution might not work in all cases, as the kvm module might 
be loaded on demand by a process accessing /dev/kvm. That process then already 
has 2k page tables.
 So I agree with Viktor: If we want to support KVM, maybe set  
vm.allocate_pgste = 1 unconditionally.

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Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1533646/+subscriptions

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Re: [Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Dimitri John Ledkov]

On 21 January 2016 at 08:38, Christian Borntraeger
 wrote:
> ok, kvm builtin certainly makes sense if you plan to use it regularly.
> So in essence its a question about: do we expect a number of users to use KVM 
> in Ubuntu or not?
>

Yes.
Last I checked, on all architectures it is a built-in, apart from
x86_64. There are two modules available on x86_64 the Intel and Amd
one, and the right one is detected and autoloaded on boot.

-- 
Regards,

Dimitri.

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Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1533646/+subscriptions

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[Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Christian Borntraeger]

ok, kvm builtin certainly makes sense if you plan to use it regularly.
So in essence its a question about: do we expect a number of users to use KVM 
in Ubuntu or not?

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Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1533646/+subscriptions

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[Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Christian Borntraeger]

the TCG emulation of QEMU does work without allocatr_pgste. 
vm.allocate_pgste=1 is necessary to use the KVM kernel module (which is used by 
qemu in kvm mode)

The main difference is that this uses 4k page tables instead of 2k page
tables on s390. So enabling pgstes will increase the page table
overhead. The difference is usually pretty small, but might become
noticeable when you have things like a big database with hundreds of
processes accessing a big area of shared memory.

Maybe something like
# cat /etc/modprobe.d/99-kvm.conf 
install kvm /sbin/sysctl vm.allocate_pgste=1; /sbin/modprobe --ignore-install 
kvm
remove kvm /sbin/sysctl vm.allocate_pgste=0; /sbin/modprobe -r --ignore-remove 
kvm

would be good enough?

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Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

To manage notifications about this bug go to:
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Re: [Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Dimitri John Ledkov]

On 20 January 2016 at 19:44, Christian Borntraeger
 wrote:
> the TCG emulation of QEMU does work without allocatr_pgste.
> vm.allocate_pgste=1 is necessary to use the KVM kernel module (which is used 
> by qemu in kvm mode)
>
> The main difference is that this uses 4k page tables instead of 2k page
> tables on s390. So enabling pgstes will increase the page table
> overhead. The difference is usually pretty small, but might become
> noticeable when you have things like a big database with hundreds of
> processes accessing a big area of shared memory.
>

Thank you for the info.

> Maybe something like
> # cat /etc/modprobe.d/99-kvm.conf
> install kvm /sbin/sysctl vm.allocate_pgste=1; /sbin/modprobe --ignore-install 
> kvm
> remove kvm /sbin/sysctl vm.allocate_pgste=0; /sbin/modprobe -r 
> --ignore-remove kvm
>
> would be good enough?
>

In newer kernel config we have kvm module as a built in, rather than a
module.

I was thinking to move vm.allocate_pgste=1 from procps package
(installed everywhere) to qemu package (installed when going to run
VMs).

-- 
Regards,

Dimitri.

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https://bugs.launchpad.net/bugs/1533646

Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

To manage notifications about this bug go to:
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[Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Dimitri John Ledkov]

cool. Is there a way to measure vm.allocate_pgste=1 overheads and is it
ok to enable by default? It's needed only on vm hosts... maybe i should
add it to the qemu package only? or like try to add systemd hackery to
only apply it on bare-metal? (well nested virtualisation is
supported...)

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https://bugs.launchpad.net/bugs/1533646

Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

To manage notifications about this bug go to:
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[Kernel-packages] [Bug 1533646] Re: Could you set vm.allocate_pgste = 1 by default?

[Tim Gardner]

Dimitri - Setting vm.allocate_pgste is a policy decision (which the
kernel typically does not make). Is there a good reason not to set it in
procps ? There is some extra overhead when vm.allocate_pgste=1.

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Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that 
setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was 
wondering if it could be set by default.

  Or not.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1533646/+subscriptions

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