Re: [Xen-devel] [PATCH v2 2/3] xen/x86: add dom0 memory sizing variants

[Juergen Gross <jgross@xxxxxxxx>]

On 06/12/2018 12:28, Jan Beulich wrote:
>>>> On 06.12.18 at 12:20, <jgross@xxxxxxxx> wrote:
>> On 06/12/2018 12:08, Jan Beulich wrote:
>>>>>> On 06.12.18 at 09:06, <jgross@xxxxxxxx> wrote:
>>>> Today the memory size of dom0 can be specified only in terms of bytes
>>>> (either an absolute value or "host-mem - value"). When dom0 shouldn't
>>>> be auto-ballooned this requires nearly always a manual adaption of the
>>>> Xen boot parameters to reflect the actual host memory size.
>>>>
>>>> Add more possibilities to specify memory sizes. Today we have:
>>>>
>>>> dom0_mem= List of ( min:<size> | max:<size> | <size> )
>>>>
>>>> with <size> being a positive or negative size value (e.g. 1G).
>>>>
>>>> Modify that to:
>>>>
>>>> dom0_mem= List of ( min:<sz> | max:<sz> | <sz> )
>>>> <sz>: <size> | [<size>+]<frac>%
>>>> <frac>: integer value < 100
>>>>
>>>> With the following semantics:
>>>>
>>>> <frac>% specifies a fraction of host memory size in percent.
>>>> <sz> is a percentage of host memory plus an offset.
>>>>
>>>> So <sz> being 1G+25% on a 256G host would result in 65G.
>>>>
>>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>>
>>> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>
>>> I notice though that ...
>>>
>>>> -static long __init parse_amt(const char *s, const char **ps)
>>>> +static int __init parse_amt(const char *s, const char **ps, struct 
>>>> memsize *sz)
>>>>  {
>>>> -    long pages = parse_size_and_unit((*s == '-') ? s+1 : s, ps) >> 
>>>> PAGE_SHIFT;
>>>> -    return (*s == '-') ? -pages : pages;
>>>> +    unsigned long val;
>>>> +    struct memsize tmp = { };
>>>> +
>>>> +    tmp.minus = (*s == '-');
>>>> +    if ( tmp.minus )
>>>> +        s++;
>>>> +
>>>> +    /* Avoid accessing s[-1] in case value starts with '%'. */
>>>> +    if ( *s == '%' )
>>>> +        return -EINVAL;
>>>> +
>>>> +    while ( isdigit(*s) )
>>>> +    {
>>>> +        val = parse_size_and_unit_or_int(s, ps, '%');
>>>> +        s = *ps;
>>>> +        if ( *s == '%' )
>>>> +        {
>>>> +            if ( !isdigit(s[-1]) || val >= 100 )
>>>> +                return -EINVAL;
>>>> +            tmp.percent = val;
>>>> +            s++;
>>>> +        }
>>>> +        else
>>>> +            tmp.nr_pages = val >> PAGE_SHIFT;
>>>> +        if ( *s == '+' )
>>>> +            s++;
>>>> +    }
>>>
>>> ... you allow more flexibility here than you document (i.e. also
>>> <percentage>+<basesize>). You may want to consider
>>> refusing something like 1G+10%+10%, though.
>>
>> Okay, should be fairly easy.
>>
>> Can I keep your R-b: with adding something like:
>>
>> +    bool percent = false;
>> ...
>> -    while ( isdigit(*s) )
>> +    while ( isdigit(*s) && !percent )
>> ...
>>          if ( *s == '%' )
>>          {
>> +            percent = true;
>> ...
> 
> Something like this, yes. The double percent value was just an
> example though, "1G+10%+1G" then too would better either work
> as written, or be refused.

Okay, I'll modify the patch accordingly and drop your R-b.


Juergen

> 
> Jan
> 


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