kernel-packages team mailing list archive

[Dimitri John Ledkov <launchpad@xxxxxxxxxxxx>]

On 20 January 2016 at 19:44, Christian Borntraeger
<borntraeger@xxxxxxxxxx> 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.

-- 
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
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.

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