Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190828073130.83800-1-namhyung@kernel.org> <20190828073130.83800-3-namhyung@kernel.org>
 <20190828144911.GR2263813@devbig004.ftw2.facebook.com> <20190831030321.GA93532@google.com>
 <20190831045815.GE2263813@devbig004.ftw2.facebook.com> <CAPhsuW42ivYU=U5E9jLMWZZgXP_Dv0C_SMFBsiXa53=6bN-=Wg@mail.gmail.com>
 <20190916152325.GD3084169@devbig004.ftw2.facebook.com> <CAPhsuW54+YNkj3fnmS6P0=eEdzZ4YvV7Yv+t-d-OnRNNgxPS+Q@mail.gmail.com>
 <CAM9d7cg_AKCyifV7xDm7sJ4=wgG_K=qu013TSTHqLiCRh9m_pg@mail.gmail.com> <20190920210411.GB2233839@devbig004.ftw2.facebook.com>
In-Reply-To: <20190920210411.GB2233839@devbig004.ftw2.facebook.com>
From:   Namhyung Kim <namhyung@kernel.org>
Date:   Wed, 2 Oct 2019 15:28:00 +0900
Message-ID: <CAM9d7cjbt6TYL_uiwu9DSiJLW-nx3P=BpWvqu-pR=DNSD2Dzdg@mail.gmail.com>
Subject: Re: [PATCH 2/9] perf/core: Add PERF_SAMPLE_CGROUP feature
To:     Tejun Heo <tj@kernel.org>
Cc:     Song Liu <liu.song.a23@gmail.com>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jiri Olsa <jolsa@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Stephane Eranian <eranian@google.com>,
        Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Tejun,

Sorry for the late reply.

On Sat, Sep 21, 2019 at 6:04 AM Tejun Heo <tj@kernel.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