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Re: [Qemu-devel] [PATCH v3 0/2] Introduce default ram size in MachineCla

From: Nikunj A Dadhania
Subject: Re: [Qemu-devel] [PATCH v3 0/2] Introduce default ram size in MachineClass
Date: Thu, 05 Mar 2015 20:32:03 +0530
User-agent: Notmuch/0.17+27~gae47d61 (http://notmuchmail.org) Emacs/24.3.1 (x86_64-redhat-linux-gnu)

Markus Armbruster <address@hidden> writes:

> Nikunj A Dadhania <address@hidden> writes:
>> Markus Armbruster <address@hidden> writes:
>>> Nikunj A Dadhania <address@hidden> writes:
>>>> Current DEFAULT_RAM_SIZE(128MB) enforced by QEMU would not work for
>>>> all machines. Introduce a default_ram_size as part of MachineClass.
>>>> The below patches has following behaviour:
>>>> 1) If the user does not provide "-m" option, machine's default ram
>>>>    size will be picked.
>>>> 2) In case the user provides memory that is lesser than machine's
>>>>    default ram size, we upscale the ram_size to machine's
>>>>    default_ram_size. A warning is displayed for the change that qemu
>>>>    has done.
>>> Please do not "improve" the user's explicit order that way.  Either
>>> execute the order as is, or reject it as invalid.
>> If there is consensus for doing this, I can change the patches
>> accordingly.
>> Rejection is also change of behaviour. Because till now, a VM would
>> start with any memory size, even if it's less that 128MB
>> (default_ram_size). With rejection, all those VMs would fail booting
>> displaying the warning. Is this OK?
> I'd stick to "don't reject".  

Agree, i have already sent v4 with those changes, as there were multiple
opinions against changing the behaviour.

> Yes, the failure mode is ugly.  But protecting the user from it is
> also somewhat problematic, because we don't generally know how much
> RAM the actual guest requires, and it's an incompatible change.  Seems
> not worth it.
> Back in 2012, we discussed rejecting RAM size less than 1MiB for PC
> machines, because SeaBIOS requires at least that much, and decided
> against it.  See
> http://www.seabios.org/pipermail/seabios/2012-August/004343.html
> If you want to pursue "reject" anyway, please make sure to split this
> into two separate patches: one patch to make the default ram size
> machine-specific, and another patch to reject user requests for less.
> [...]


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