Re: [Xen-devel] Vmap allocator fails to allocate beyond 128MB

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 16/02/15 10:50, Vijay Kilari wrote:
> On Mon, Feb 16, 2015 at 3:58 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
>> On 16/02/15 10:17, Vijay Kilari wrote:
>>
>> Hello Vijay,
>>
>>>   For ThunderX/arm64 this issue needs to be fixed.
>>> Could you please comment on this?
>>
>> AFAICS, x86 is also using a 1G area for the vmap. Does it mean that x86
>> never use vmap for more than 128M?
> 
> I think for x86 there is no problem. It works beyond 128M

Did you test it? The code seems common enough to make the problem
appears on x86.

>>
>>> I could think of below
>>>
>>>         1) Add new call for ARM under CONFIG_ARM_32/CONFIG_ARM_64
>>> in vm_init() and manage map_pages_to_xen(va, 0, vm_low - nr, 
>>> MAP_SMALL_PAGES);
>>> with different function call for arm that would not make any pte
>>> entries for vm_bitmap pages.
>>> This avoids change to x86
>>>
>>>         2) Remove map_pages_to_xen(va, 0, vm_low - nr,
>>> MAP_SMALL_PAGES) from vm_init
>>> and add new architecture specific for initializing vm_bitmap pages.
>>> But this touches
>>> x86 code.
>>
>> I don't know which approach is the best, and I though you already talked
>> about it with Jan... But in general a generic approach is better than a
>> per-architecture solution.
> 
> When I say architecture specific, I mean, a common function will be
> created and implemented in architecture specific files similar to
> map_pages_to_xen. This new function will wrap the required code
> for per-architecture.

I would advice you to send an RFC on the mailing list. So we have a base
to talk about it.

Regards,

-- 
Julien Grall

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