linux-kernel - Re: [PATCH 2/4] perf tools: Fix max mmap

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Date:	Mon, 09 Dec 2013 16:00:57 +0200
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/4] perf tools: Fix max mmap_pages

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@...el.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
>>
> 
> 

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