From: Robert Foss <robert.foss@collabora.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: corbet@lwn.net, akpm@linux-foundation.org, vbabka@suse.cz,
koct9i@gmail.com, hughd@google.com, n-horiguchi@ah.jp.nec.com,
minchan@kernel.org, john.stultz@linaro.org,
ross.zwisler@linux.intel.com, jmarchan@redhat.com,
hannes@cmpxchg.org, keescook@chromium.org,
viro@zeniv.linux.org.uk, gorcunov@openvz.org,
plaguedbypenguins@gmail.com, rientjes@google.com,
eric.engestrom@imgtec.com, jdanis@google.com, calvinowens@fb.com,
adobriyan@gmail.com, jann@thejh.net, sonnyrao@chromium.org,
kirill.shutemov@linux.intel.com, ldufour@linux.vnet.ibm.com,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
Ben Zhang <benzh@chromium.org>, Bryan Freed <bfreed@chromium.org>,
Filipe Brandenburger <filbranden@chromium.org>,
Mateusz Guzik <mguzik@redhat.com>
Subject: Re: [PACTH v2 0/3] Implement /proc/<pid>/totmaps
Date: Mon, 15 Aug 2016 12:25:10 -0400 [thread overview]
Message-ID: <a73f2836-da8a-f820-c1ac-c2314c9a0248@collabora.com> (raw)
In-Reply-To: <20160815134227.GE3360@dhcp22.suse.cz>
On 2016-08-15 09:42 AM, Michal Hocko wrote:
> On Mon 15-08-16 09:00:04, Robert Foss wrote:
>>
>>
>> On 2016-08-14 05:04 AM, Michal Hocko wrote:
>>> On Fri 12-08-16 18:04:19, robert.foss@collabora.com wrote:
>>>> From: Robert Foss <robert.foss@collabora.com>
>>>>
>>>> This series implements /proc/PID/totmaps, a tool for retrieving summarized
>>>> information about the mappings of a process.
>>>
>>> The changelog is absolutely missing the usecase. Why do we need this?
>>> Why existing interfaces are not sufficient?
>>
>> You are absolutely right, more info information is in 1/3.
>
> Patch 1 is silent about the use case as well. It is usually recommended
> to describe the motivation for the change in the cover letter.
I'll change it for v3.
>
>> But the gist of it is that it provides a faster and more convenient way of
>> accessing the information in /proc/PID/smaps.
>
> I am sorry to insist but this is far from a description I was hoping
> for. Why do we need a more convenient API? Please note that this is a
> userspace API which we will have to maintain for ever. We have made many
> mistakes in the past where exporting some information made sense at the
> time while it turned out being a mistake only later on. So let's make
> sure we will not fall into the same trap again.
>
> So please make sure you describe the use case, why the current API is
> insufficient and why it cannot be tweaked to provide the information you
> are looking for.
>
I'll add a more elaborate description to the v3 cover letter.
In v1, there was a discussion which I think presented the practical
applications rather well:
https://lkml.org/lkml/2016/8/9/628
or the qoute from Sonny Rao pasted below:
> The use case is to speed up monitoring of
> memory consumption in environments where RSS isn't precise.
>
> For example Chrome tends to many processes which have hundreds of VMAs
> with a substantial amount of shared memory, and the error of using
> RSS rather than PSS tends to be very large when looking at overall
> memory consumption. PSS isn't kept as a single number that's exported
> like RSS, so to calculate PSS means having to parse a very large smaps
> file.
>
> This process is slow and has to be repeated for many processes, and we
> found that the just act of doing the parsing was taking up a
> significant amount of CPU time, so this patch is an attempt to make
> that process cheaper.
If a reformatted version of this still isn't adequate or desirable for
the cover-letter, please give me another heads up.
Thanks!
next prev parent reply other threads:[~2016-08-15 16:25 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-12 22:04 [PACTH v2 0/3] Implement /proc/<pid>/totmaps robert.foss
2016-08-12 22:04 ` [PACTH v2 1/3] mm, proc: " robert.foss
2016-08-13 14:39 ` Jann Horn
2016-08-15 13:57 ` Robert Foss
2016-08-15 20:14 ` Robert Foss
2016-08-12 22:04 ` [PACTH v2 2/3] Documentation/filesystems: Fixed typo robert.foss
2016-08-12 22:04 ` [PACTH v2 3/3] Documentation/filesystems: Added /proc/PID/totmaps documentation robert.foss
2016-08-14 9:04 ` [PACTH v2 0/3] Implement /proc/<pid>/totmaps Michal Hocko
2016-08-15 13:00 ` Robert Foss
2016-08-15 13:42 ` Michal Hocko
2016-08-15 16:25 ` Robert Foss [this message]
2016-08-16 7:12 ` Michal Hocko
2016-08-16 16:46 ` Robert Foss
2016-08-17 8:22 ` Michal Hocko
2016-08-17 9:31 ` Jann Horn
2016-08-17 13:03 ` Michal Hocko
2016-08-17 16:48 ` Robert Foss
2016-08-17 18:57 ` Sonny Rao
2016-08-18 7:44 ` Michal Hocko
2016-08-18 17:47 ` Sonny Rao
2016-08-18 18:01 ` Michal Hocko
2016-08-18 21:05 ` Robert Foss
2016-08-19 6:27 ` Sonny Rao
2016-08-19 2:26 ` Minchan Kim
2016-08-19 6:47 ` Sonny Rao
2016-08-19 8:05 ` Michal Hocko
2016-08-19 18:20 ` Sonny Rao
2016-08-22 0:07 ` Minchan Kim
2016-08-22 7:40 ` Michal Hocko
2016-08-22 14:12 ` Minchan Kim
2016-08-22 14:37 ` Robert Foss
2016-08-22 16:45 ` Michal Hocko
2016-08-22 17:29 ` Michal Hocko
2016-08-22 17:47 ` Michal Hocko
2016-08-23 8:26 ` Michal Hocko
2016-08-23 14:33 ` utime accounting regression since 4.6 (was: Re: [PACTH v2 0/3] Implement /proc/<pid>/totmaps) Michal Hocko
2016-08-23 21:46 ` Rik van Riel
2016-08-24 16:56 ` Michal Hocko
2016-09-30 9:49 ` Michal Hocko
2016-09-30 12:35 ` Rik van Riel
2016-08-19 6:43 ` [PACTH v2 0/3] Implement /proc/<pid>/totmaps Sonny Rao
2016-08-19 7:59 ` Michal Hocko
2016-08-19 17:57 ` Sonny Rao
2016-08-22 7:54 ` Michal Hocko
2016-08-22 22:44 ` Sonny Rao
2016-08-24 10:14 ` Marcin Jabrzyk
2016-08-30 8:20 ` Michal Hocko
2016-08-29 14:37 ` Michal Hocko
2016-08-30 8:15 ` Michal Hocko
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