Re: [Xen-devel] [PATCH v3 3/4] xen: refactor debugtrace data

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.09.2019 12:31, Juergen Gross wrote:
> On 03.09.19 12:16, Jan Beulich wrote:
>> On 28.08.2019 10:00, Juergen Gross wrote:
>>> +static unsigned int debugtrace_kilobytes = 128;
>>
>> Since you touch this anyway, add __initdata? Maybe also move it
>> next to its integer_param()?
> 
> This is modified in patch 4 again, and there I need it in the running
> system for support of cpu hotplug with per-cpu buffers.

Right, I've meanwhile noticed this. Hence it's fine to keep as is.

>>> @@ -165,12 +171,14 @@ static int __init debugtrace_init(void)
>>>           return 0;
>>>   
>>>       order = get_order_from_bytes(bytes);
>>> -    debugtrace_buf = alloc_xenheap_pages(order, 0);
>>> -    ASSERT(debugtrace_buf != NULL);
>>> +    data = alloc_xenheap_pages(order, 0);
>>> +    if ( !data )
>>> +        return -ENOMEM;
>>>   
>>> -    memset(debugtrace_buf, '\0', bytes);
>>> +    memset(data, '\0', bytes);
>>>   
>>> -    debugtrace_bytes = bytes;
>>> +    data->bytes = bytes - sizeof(*data);
>>> +    debtr_data = data;
>>
>> The allocation may end up being almost twice as big as what gets
>> actually used this way. Wouldn't it make sense to re-calculate
>> "bytes" from "order"?
> 
> Yes, you are right.

Actually I wasn't, which I did notice seeing the relevant piece
of code getting touched in patch 4:

    while ( (kbytes = (debugtrace_kilobytes & (debugtrace_kilobytes-1))) != 0 )
        debugtrace_kilobytes = kbytes;

Jan

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