Re: [Qemu-devel] [PATCH] Introduce machine specific default memory size

[Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>]

Thomas Huth <thuth@linux.vnet.ibm.com> writes:

> On Wed, 04 Mar 2015 14:59:13 +0530
> Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> wrote:
>
>> Thomas Huth <thuth@linux.vnet.ibm.com> writes:
>> 
>> > On Wed, 04 Mar 2015 14:34:27 +0530
>> > Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> wrote:
>> >
>> >> Thomas Huth <thuth@linux.vnet.ibm.com> writes:
>> >> 
>> >> > On Wed, 04 Mar 2015 14:00:17 +0530
>> >> > Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> wrote:
>> >> >
>> >> >> Markus Armbruster <armbru@redhat.com> writes:
>> >> >> 
>> >> >> > Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> writes:
>> >> >> >
>> >> >> >> diff --git a/vl.c b/vl.c
>> >> >> >> index eb89d62..dd56754 100644
>> >> >> >> --- a/vl.c
>> >> >> >> +++ b/vl.c
>> >> >> >> @@ -4053,6 +4053,18 @@ int main(int argc, char **argv, char **envp)
>> >> >> >>          exit(1);
>> >> >> >>      }
>> >> >> >>  
>> >> >> >> +    if (machine_class->default_ram_size && ram_size < machine_class->default_ram_size) {
>> >> >> >> +        fprintf(stderr, "qemu: %s guest ram size defaulting to %ld MB\n",
>> >> >> >> +                machine_class->name,
>> >> >> >> +                machine_class->default_ram_size / (1024 * 1024));
>> >> >> >
>> >> >> > If the user explicitly asks for something, we either provide it
>> >> >> > silently, or we error out.  This does neither.  Why?
>> >> >> 
>> >> >> In case the user has provided memory not enough to boot the machine, I
>> >> >> could error out. My idea was to have a sane default which is provided by
>> >> >> the machine.
>> >> >> 
>> >> >> Initially, I had just "ram_size == default_ram_size", but then it was
>> >> >> allowing "-m 128M" to go through. And the VM would not boot. 
>> >> >> 
>> >> >> This can as well be converted to an error report and fail here to boot
>> >> >> the VM.
>> >> >
>> >> > What does exactly fail with 128MB? Linux? 
>> >> 
>> >> Linux kernel, and not much info as well on the console.
>> >
>> > Ok, but then I think it should still be possible to specify -m 128M on
>> > the command line - in case the user wants to run an older Linux which
>> > still works fine with that amount of memory.
>> 
>> But how do we distinguish whether its old/new kernel in the distro?
>> 
>> And the older kernel will boot with more memory, while the reverse isnt
>> true.
>
> True, and it's IMHO certainly ok to increase the default memory size -

> I just wanted to say that you should not disallow "-m 128M" in case the
> users know what they are doing.

That becomes a little bit tricky, as 128MB can come from
default_ram_size and from the user as well. 

So here I am only changing the machine class for sPAPR. I have tried few
distro installations and none of them boot with qemu default
memory(128MB). Moreover, the installer kernel does not tell what went
wrong. It silently goes till a point and is stuck.

Regards
Nikunj