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Re: [Xen-devel] [PATCH] xen/arm: increase default dom0_mem to 512M
Hi Stefano, On 16/02/17 20:17, Stefano Stabellini wrote:
On Thu, 16 Feb 2017, Julien Grall wrote:Hi Stefano, On 15/02/2017 23:05, Stefano Stabellini wrote:The default dom0_mem is 128M which is not sufficient to boot a Ubuntu based Dom0. Increase it to 512M. Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>I am not a big fan of increasing the default value. 128M is plenty enough if you use a small DOM0 (e.g buildroot or yocto) and people may rely on it because it is the default value in the documentation (see docs/misc/xen-command-line.markdown). Also, 512M may boot Ubuntu for you but it might not be the case in all the configuration. There is no perfect default value, but I think the smaller is better. Looking at the documentation, it looks like x86 is using 128MB or 1/16 of the memory (whichever is smaller). But to be fair, I am not even sure why there is a default value, it is quite easy to specify the amount of memory used by DOM0 on the command line.This is a topic particularly prone to bike-shedding :-) Like you wrote, there is no perfect default value. The problem with 128M is that Dom0 will fail to boot without any meaningful errors. I think it makes for a poor out of the box experience: the user is trying to boot Xen for the first time on her board, she hasn't customized much yet, and she has to waste a couple of hours to figure out why Dom0 is crashing. On the other end, people that are trying to use as little memory as possible, they are well past the first Xen boot, and they are most certainly aware of the dom0_mem parameter. In other words, setting dom0_mem to 128M by default hurts first time users without helping seasoned users very much. Rather than having dom0_mem=128M by default, causing a dom0 crash without any obvious errors, I would rather crash Xen explicitly if dom0_mem is not set. That way, the user is forced to type in the dom0_mem parameter and could more easily guess why dom0 is crashing.
Crashing if dom0_mem is not set would be my preferred way. At least we won't have a default value that is a bit random. Ubuntu uses 512MB today, but who knows tomorrow?
In any case, any change on the command line needs to be documented in docs/misc/xen-command-line.markdown.
Cheers, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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