Re: [PATCH v3 8/8] xen: arm: allocate more than one bank for 1:1 domain 0 if needed

[Julien Grall <julien.grall@linaro.org>]

Hi Ian,

On 27/06/14 10:24, Ian Campbell wrote:
>> This has to be: bits <= (...). Indeed, we want to try all possible zone.
>
> Damn. I tested this on midway with "dom0_mem=128M mem=1G" and saw a
> failure (which is fixed in this iteration). But obviously midway and
> vexpress differ in their physical RAM addresses which caused me to miss
> this second failure.
>
> Have you tried that change? bits < 32 gives you 32-bits (i.e. 0..31)
> which should cover everything up to 4G. Or else I'm misremembering some
> quirk of the allocation interface.

Yes, without the change "<=" I was unable to allocate the first bank.

The memory layout is
(XEN) Checking for initrd in /chosen
(XEN) RAM: 0000000080000000 - 000000009fffffff
(XEN) RAM: 00000000a0000000 - 00000000bfffffff
(XEN)
(XEN) MODULE[1]: 000000009fee6000 - 000000009feea000
(XEN) MODULE[2]: 00000000a0008000 - 00000000a033f458
(XEN)  RESVD[0]: 0000000081f00000 - 0000000081f04000
(XEN)  RESVD[1]: 000000009fee6000 - 000000009feea000

> Does vexpress really have memory high enough up that excluding bits==32
> excludes it? I thought it was down in the 1-3GB range.

The first bank allocating is situated just above 2GB
BANK[0] 0x000000a8000000-0x000000b0000000

But I'm unable to find enough memory unless when I pass bits=32 to the 
allocator.

>> I'm looking why Xen doesn't try to allocate in lower memory the first bank.
>
> Usually it means that at least single page is allocated in each 128MB
> block lower down, which can happen depending on how your boot modules
> are laid out.

With my current layout (see above), I should have space in the first 
bank (around 0x80000000). I don't really understand why Xen is not 
trying to use it.

> I did consider making
> min_low_order = get_order_from_bytes(min_t(paddr_t, dom0_mem/4, MB(128)));
>
> i.e. for a dom0_mem <= 128MB allowing to be split into 4x32MB banks if
> necessary. Or perhaps /2 would be better since 32MB is small enough that
> we might have trouble with placing the kernel and modules etc in a
> single bank.

Require a 128Mb hole in the memory doesn't seem too mad. I would keep 
this minimum value.

Regards,

-- 
Julien Grall