linux-kernel - Re: [PATCH 2/9] perf/core: Add PERF_SAMPLE

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Message-ID: <CAM9d7cjbt6TYL_uiwu9DSiJLW-nx3P=BpWvqu-pR=DNSD2Dzdg@mail.gmail.com>
Date:   Wed, 2 Oct 2019 15:28:00 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Song Liu <liu.song.a23@...il.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 2/9] perf/core: Add PERF_SAMPLE_CGROUP feature

Hi Tejun,

Sorry for the late reply.

On Sat, Sep 21, 2019 at 6:04 AM Tejun Heo <tj@...nel.org> wrote:
>
> On Fri, Sep 20, 2019 at 05:47:45PM +0900, Namhyung Kim wrote:
> > Thanks for the sharing information!  For 32-bit, while the ino itself is not
> > monotonic, gen << 32 + ino is monotonic right?  I think we can use the
>
> It's not.  gen gets incremented on every allocation, so it has not
> high but still realistic chance of collisions.

In __kernfs_new_node(), gen gets increased only if idr_alloc_cyclic()
returns lower than the cursor...  I'm not sure you talked about it.

Thanks
Namhyung