Re: [Xen-devel] [PATCH v5 08/10] xen/arm: Add relinquish_p2m_mapping to remove reference on every mapped page

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 12/17/2013 02:52 PM, Ian Campbell wrote:
> On Tue, 2013-12-17 at 14:45 +0000, Julien Grall wrote:
>> On 12/17/2013 02:42 PM, Ian Campbell wrote:
>>> On Tue, 2013-12-17 at 14:40 +0000, Julien Grall wrote:
>>>> On 12/17/2013 09:26 AM, Ian Campbell wrote:
>>>>> On Mon, 2013-12-16 at 17:37 +0000, Julien Grall wrote:
>>>>>> +        if ( op == RELINQUISH && count == LPAE_ENTRIES &&
>>>>>> +             hypercall_preempt_check() )
>>>>>> +        {
>>>>>
>>>>> If hypercall_preempt_check returns false the first time it is called
>>>>> then you won't ever try again. I think you want
>>>>>   (count+1 % LPAE_ENTRIES) == 0
>>>>> (the +1 avoids preempting without having done any work yet)
>>>>
>>>> I don't think we need +1 because count is increment each round just
>>>> before the check.
>>>
>>> Ah yes, if the increment has already happened then good.
>>>
>>>> Is a solution as Jan made for x86 would be more appropriate?
>>>
>>> It's about equivalent I think? I'd hope the compiler would take a mod
>>> 2^N and turn it into a mask, but I suppose you never know...
>>
>> I was talking about adding a greater increment when it's a foreign mapping.
> 
> Like I said in the other subthread:
> 
>         BTW, Jan's approach in his x86 fix was to preempt every 2MB of present
>         or 32MB of non-present mappings, which makes sense because you skip
>         through the non-present ones more quickly. It'd be nice but lets not
>         hold up the series if it isn't trivial to achieve.

Sorry I didn't yet read this mail. I will try to implement the same
behavior for the next version.

-- 
Julien Grall

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