Re: [Xen-users] Xen memory allocation for dom0 and domU

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2015-02-03 at 22:37 -0500, Jintack Lim wrote:
> Hi all,
> 
> This is a kind of basic question.
> 
> I have a cubietruck (armv7) board which has 2G of memory.
> I'm using Xen 4.5.
> 
> I want to allocate 1.5G to domU and as much as possible to dom0.
> It turned out that I only can allocate 128M of memory for dom0.
> When I allocated 256M or 384M, I got an error.
> Log is attached at the bottom.

Jut to make sure I understand: if you boot dom0 with 128M then you can
start a 1.5G domU, but if you boot dom0 with 256M then you cannot start
the 1.5G domU?

> I'm looking at tools/libxc/xc_dom_arm.c,
> and xen/docs/misc/libxl_memory.txt
> However, if there is any written guide(or rule) to allocate memory for
> dom0 and domU, it'll be much helpful!!

The only real guide is to make sure the system has enough free RAM, or
is at least able to balloon dom0 down to free the needed memory.

> domainbuilder: detail: populate_one_size: populated 0x2ae/0x300
> entries with shift 9
> domainbuilder: detail: populate_one_size: populated 0x343/0xa400
> entries with shift 0
> domainbuilder: detail: populate_guest_memory: Not enough RAM
> xc: error: panic: xc_dom_boot.c:154: xc_dom_boot_mem_init: can't
> allocate low memory for domain: Out of memory

It appears you are just running out of memory, what does "xl info" in
dom0 say when you have just booted (i.e. without having started a
guest)? The most interesting numbers will be total_memory and
free_memory.

How are you configuring the amount of dom0 memory? With dom0_mem on the
hypervisor command line?

Don't forget that Xen itself will consume some RAM, according to your
numbers it's something between 256M and 350M on this system (that's more
than my gut feeling expects, but not way out).

Ian.


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