linux-kernel - Re: [PATCH 02/26] perf: Introduce mmap3 version of mmap event

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Date:   Mon, 14 Sep 2020 11:08:11 +0200
From:   peterz@...radead.org
To:     Stephane Eranian <eranian@...gle.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Song Liu <songliubraving@...com>,
        "Frank Ch. Eigler" <fche@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 02/26] perf: Introduce mmap3 version of mmap event

On Sun, Sep 13, 2020 at 11:41:00PM -0700, Stephane Eranian wrote:
> On Sun, Sep 13, 2020 at 2:03 PM Jiri Olsa <jolsa@...nel.org> wrote:
> what happens if I set mmap3 and mmap2?
> 
> I think using mmap3 for every mmap may be overkill as you add useless
> 20 bytes to an mmap record.
> I am not sure if your code handles the case where mmap3 is not needed
> because there is no buildid, e.g, anonymous memory.
> It seems to me you've written the patch in such a way that if the user
> tool supports mmap3, then it supersedes mmap2, and thus
> you need all the fields of mmap2. But if could be more interesting to
> return either MMAP2 or MMAP3 depending on tool support
> and type of mmap, that would certainly save 20 bytes on any anon mmap.
> But maybe that logic is already in your patch and I missed it.

That, and what if you don't want any of that buildid nonsense at all? I
always kill that because it makes perf pointlessly slow and has
absolutely no upsides for me.