Re: [PATCH 2/4] perf tools: Fix max mmap_pages

Adrian Hunter
2013-12-09T13:53:02Z

On 09/12/13 15:35, Jiri Olsa wrote:
> On Mon, Dec 09, 2013 at 03:18:38PM +0200, Adrian Hunter wrote:
>> 'SIZE_MAX / page_size' is an upper limit for
>> the maximum number of mmap pages, not a lower
>> limit. Change the condition accordingly.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>> ---
>> tools/perf/util/evlist.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>> index 4d0945c..98ec96b 100644
>> --- a/tools/perf/util/evlist.c
>> +++ b/tools/perf/util/evlist.c
>> @@ -754,7 +754,7 @@ int perf_evlist__parse_mmap_pages(const struct option *opt, const char *str,
>> unsigned long max = UINT_MAX;
>> long pages;
>>
>> - if (max < SIZE_MAX / page_size)
>> + if (max > SIZE_MAX / page_size)
>> max = SIZE_MAX / page_size;
>
> I agree with the change.. but it looks like the check
> is superfluos, maybe we want to define max as:
>
> unsigned long max = SIZE_MAX / page_size

I think it is OK because mmap_pages (in struct perf_record_opts) is an
unsigned int i.e.

max = MIN(UINT_MAX, SIZE_MAX / 4096)

c.f.
32-bit 64-bit
UINT_MAX 2^32 - 1 2^32 - 1
SIZE_MAX 2^32 - 1 2^64 - 1
SIZE_MAX / 4096 2^20 - 1 2^52 - 1

So on 32-bit the max is SIZE_MAX / 4096 but on
64-bit the max is UINT_MAX

>
> ?
>
> jirka
>>
>> pages = parse_pages_arg(str, 1, max);
>> --
>> 1.7.11.7
>>
>
>