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[Qemu-devel] [Bug 1801933] Re: default memory parameter too small on x86

From: Daniel Berrange
Subject: [Qemu-devel] [Bug 1801933] Re: default memory parameter too small on x86_64 today
Date: Wed, 05 Dec 2018 11:20:38 -0000

IMHO, if achieving ease of use comparable to VirtualBox is your
benchmark target, then launching QEMU directly is really the wrong way
to approach things. QEMU is a very low level piece of infrastructure not
a complete end user desktop solution. For that it is better to look at
using an application such as virt-manager, or GNOME Boxes. These provide
higher level solution over QEMU and do smart things during installation,
using libosinfo to automatically determine the best memory, disk,
network, etc settings for each particular guest OS rather than relying
on some hardcoded defaults.

That said all said, I don't rule out that we could change our memory
defaults, but picking an optimal value is hard. Even 500 MB is
considered to be unsupported from a RHEL-7 pov - the documented minimum
for RHEL-7 is 1 GB per vCPU. The installer is quite likely to crash with
500 MB depending on what options you select durin intsall.

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  default memory parameter too small on x86_64 today

Status in QEMU:

Bug description:
  Launching a centos74 iso VM today does not work anymore on x86_64
  without increasing the size of the memory parameter. For example with
  this command :

  $ /opt/qemu-3.0.0/bin/qemu-system-x86_64 --curses   -enable-kvm -drive
  file=file.dd,index=0,media=disk -drive file=centos-

  [    3.047614] Failed to execute /init
  [    3.048315] Kernel panic - not syncing: No init found.  Try passing init= 
option to kernel. See Linux Documentation/init.txt for guidance.
  [    3.049258] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 

  Increasing the size from the default 128MiB to 512MiB let the VM works 
without problem.
  So, ok, it's not a qemu problem, it's more a "User problem" and interface 
problem for me.
  But it push me in the end to launch VirtualBox instead of qemu, because the 
default parameter does not work anymore... And I had no time to investigate why 
it does not work because the message is not visible.
  Debian iso with the same command line for example show a message to tell me 
that there is not enough memory, so it help me to track the real issue behind.

  But... In the end, I think today, the default memory parameter on x86_64 is 
too small and it can lead some people like me to switch to VirtualBox.
  VirtualBox, in the wizard is set by default to 4MiB Ram size, which tell 
you... Ok I need to put more. And, you know that 4MiB is not enough in the end.



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