linux-kernel - Re: [PATCH v6 00/12] extend task comm from 16 to 24

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Message-ID: <20211025170503.59830a43@gandalf.local.home>
Date:   Mon, 25 Oct 2021 17:05:03 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Yafang Shao <laoar.shao@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Valentin Schneider <valentin.schneider@....com>,
        "Zhang, Qiang" <qiang.zhang@...driver.com>, robdclark@...omium.org,
        Christian Brauner <christian@...uner.io>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        dennis.dalessandro@...nelisnetworks.com,
        mike.marciniszyn@...nelisnetworks.com,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>, linux-rdma@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, linux-perf-users@...r.kernel.org,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel test robot <oliver.sang@...el.com>,
        kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH v6 00/12] extend task comm from 16 to 24

On Mon, 25 Oct 2021 11:10:09 -0700
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> It looks like a churn that doesn't really address the problem.
> If we were to allow long names then make it into a pointer and use 16 byte
> as an optimized storage for short names. Any longer name would be a pointer.
> In other words make it similar to dentry->d_iname.

That would be quite a bigger undertaking too, as it is assumed throughout
the kernel that the task->comm is TASK_COMM_LEN and is nul terminated. And
most locations that save the comm simply use a fixed size string of
TASK_COMM_LEN. Not saying its not feasible, but it would require a lot more
analysis of the impact by changing such a fundamental part of task struct
from a static to something requiring allocation.

Unless you are suggesting that we truncate like normal the 16 byte names
(to a max of 15 characters), and add a way to hold the entire name for
those locations that understand it.

-- Steve