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

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Message-ID: <CAM9d7cg_AKCyifV7xDm7sJ4=wgG_K=qu013TSTHqLiCRh9m_pg@mail.gmail.com>
Date:   Fri, 20 Sep 2019 17:47:45 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Song Liu <liu.song.a23@...il.com>
Cc:     Tejun Heo <tj@...nel.org>, 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

Hello Song,

On Thu, Sep 19, 2019 at 3:43 PM Song Liu <liu.song.a23@...il.com> wrote:

> Sharing some offline discussions with Tejun.
>
> ino in current kernfs is not a good unique ID for cgroup, because it doesn't
> increase monotonically. So we need to improve kernfs.
>
> For 64-bit, we can make the ino monotonic, and use it as the ID.
> For 32-bit, we need to make the ino monotonic. and use <ino> and <gen>
> as the 64-bit ID.

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
same logic of kernfs id allocation, but not sure what the problem Tejun
mentioned before is.

Thanks,
Namhyung