linux-kernel - Re: [PATCH 1/2] pidmap(2)

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Date:   Wed, 6 Sep 2017 12:04:09 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Tatsiana Brouka <Tatsiana_Brouka@...m.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Aliaksandr Patseyenak <Aliaksandr_Patseyenak1@...m.com>
Subject: Re: [PATCH 1/2] pidmap(2)

On 9/6/17, Randy Dunlap <rdunlap@...radead.org> wrote:
> On 09/05/17 15:53, Andrew Morton wrote:
>> On Tue, 5 Sep 2017 22:05:00 +0300 Alexey Dobriyan <adobriyan@...il.com>
>> wrote:
>>
>>> Implement system call for bulk retrieveing of pids in binary form.
>>>
>>> Using /proc is slower than necessary: 3 syscalls + another 3 for each
>>> thread +
>>> converting with atoi().
>>>
>>> /proc may be not mounted especially in containers. Natural extension of
>>> hidepid=2 efforts is to not mount /proc at all.
>>>
>>> It could be used by programs like ps, top or CRIU. Speed increase will
>>> become more drastic once combined with bulk retrieval of process
>>> statistics.
>>
>> The patches are performance optimizations, but their changelogs contain
>> no performance measurements!
>>
>> Demonstration of some compelling real-world performance benefits would
>> help things along a lot.
>>
>
> also, I expect that the tiny kernel people will want kconfig options for
> these syscalls.

We'll add it but the question if it is a good idea. Ideally these system calls
should be mandatory and /proc optional.

$ size kernel/pidmap.o fs/fdmap.o
   text    data     bss     dec     hex filename
    560       0       0     560     230 kernel/pidmap.o
    617       0       0     617     269 fs/fdmap.o