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

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Message-ID: <20180827083303.GD24695@krava>
Date:   Mon, 27 Aug 2018 10:33:03 +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 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?

jirka