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Subject: Re: [PATCH v1] proc: Implement /proc/self/meminfo
To:     Chris Down <chris@chrisdown.name>, legion@kernel.org
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Linux Containers <containers@lists.linux.dev>,
        Linux Containers <containers@lists.linux-foundation.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>
References: <ac070cd90c0d45b7a554366f235262fa5c566435.1622716926.git.legion@kernel.org>
 <YLi+JoBwfLtqVGiP@chrisdown.name>
From:   "Enrico Weigelt, metux IT consult" <lkml@metux.net>
Message-ID: <b8c86081-503c-3671-2ea3-dd3a0950ce25@metux.net>
Date:   Wed, 9 Jun 2021 10:16:25 +0200
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On 03.06.21 13:33, Chris Down wrote:

Hi folks,


> Putting stuff in /proc to get around the problem of "some other metric I 
> need might not be exported to a container" is not a very compelling 
> argument. If they want it, then export it to the container...
> 
> Ultimately, if they're going to have to add support for a new 
> /proc/self/meminfo file anyway, these use cases should just do it 
> properly through the already supported APIs.

It's even a bit more complex ...

/proc/meminfo always tells what the *machine* has available, not what a
process can eat up. That has been this way even long before cgroups.
(eg. ulimits).

Even if you want a container look more like a VM - /proc/meminfo showing
what the container (instead of the machine) has available - just looking
at the calling task's cgroup is also wrong. Because there're cgroups
outside containers (that really shouldn't be affected) and there're even
other cgroups inside the container (that further restrict below the
container's limits).

BTW: applications trying to autotune themselves by looking at
/proc/meminfo are broken-by-design anyways. This never has been a valid
metric on how much memory invididual processes can or should eat.


--mtx

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@metux.net -- +49-151-27565287