linux-kernel - Re: [PATCH v2 1/2]: perf util: map data buffer for preserving collected data

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Date:   Tue, 28 Aug 2018 10:45:22 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 1/2]: perf util: map data buffer for preserving
 collected data

On Mon, Aug 27, 2018 at 12:02:35PM +0300, Alexey Budankov wrote:
> Hi,
> 
> On 27.08.2018 11:33, Jiri Olsa wrote:
> > On Thu, Aug 23, 2018 at 07:42:09PM +0300, Alexey Budankov wrote:
> > 
> > SNIP
> > 
> >> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
> >> index fc832676a798..e71d46cb01cc 100644
> >> --- a/tools/perf/util/mmap.c
> >> +++ b/tools/perf/util/mmap.c
> >> @@ -155,6 +155,10 @@ void __weak auxtrace_mmap_params__set_idx(struct auxtrace_mmap_params *mp __mayb
> >>  
> >>  void perf_mmap__munmap(struct perf_mmap *map)
> >>  {
> >> +	if (map->data != NULL) {
> >> +		munmap(map->data, perf_mmap__mmap_len(map));
> >> +		map->data = NULL;
> >> +	}
> >>  	if (map->base != NULL) {
> >>  		munmap(map->base, perf_mmap__mmap_len(map));
> >>  		map->base = NULL;
> >> @@ -190,6 +194,14 @@ int perf_mmap__mmap(struct perf_mmap *map, struct mmap_params *mp, int fd)
> >>  		map->base = NULL;
> >>  		return -1;
> >>  	}
> >> +	map->data = mmap(NULL, perf_mmap__mmap_len(map), PROT_READ | PROT_WRITE,
> >> +			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> > 
> > hum, why does map->data need to be mmap-ed?
> 
> The same way as for kernel buffers. If you see better alternatives it could be applied.

I meant why not just allocate them with mmaloc?

jirka