[Devel] Re: [lxc-devel] Memory Resources

[Krzysztof Taraszka]

2009/8/24 Daniel Lezcano <daniel.lezcano at free.fr>

> Krzysztof Taraszka wrote:
>
>> 2009/8/24 Daniel Lezcano <daniel.lezcano at free.fr>
>>
>>
>>
>>> Krzysztof Taraszka wrote:
>>>
>>>
>>>
>>>> 2009/8/24 Daniel Lezcano <dlezcano at fr.ibm.com>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>> Krzysztof Taraszka wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> 2009/8/24 Daniel Lezcano <daniel.lezcano at free.fr>
>>>>>>
>>>>>>  Krzysztof Taraszka wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>  2009/8/23 Daniel Lezcano <daniel.lezcano at free.fr>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> (...)
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>  With the lxc tools I did:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>    lxc-execute -n foo /bin/bash
>>>>>>>>>    echo 268435456 > /cgroup/foo/memory.limit_in_bytes
>>>>>>>>>    mount --bind /cgroup/foo/memory.meminfo /proc/meminfo
>>>>>>>>>    for i in $(seq 1 100); do sleep 3600 & done
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>> (...)
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>  :)
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>  hmmm... I think that access to the cgroup inside container is very
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>> risk
>>>>>>>> because I am able to manage for example memory resources (what if I
>>>>>>>> am
>>>>>>>> not
>>>>>>>> the host owner and... I can give me via non-secure mounted /cgroup
>>>>>>>> (inside
>>>>>>>> container) all available memory resources...).
>>>>>>>> I think that the /proc/meminfo should be pass to the container in
>>>>>>>> the
>>>>>>>> other
>>>>>>>> way, but this is the topic for the other thread.
>>>>>>>>
>>>>>>>>
>>>>>>>>  It is not a problem, I did it in this way because it's easy to test
>>>>>>>> but
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> in
>>>>>>> a real use case, the memory limit is setup by the lxc configuration
>>>>>>> file
>>>>>>> and
>>>>>>> the cgroup directory will be no longer accessible from the container.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> So.. how there will be another method (more secure) for giving
>>>>>> /proc/meminfo
>>>>>> with limits to the container, right?
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> Same method. The lxc tools can be configured with a fstab to mount more
>>>>> mount points, furthermore if memory.meminfo is available I will add the
>>>>> code
>>>>> to mount it automatically to /proc/meminfo in the lxc tools.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> Hmm... setup_fs() from lxc_init.c or another way?
>>>>
>>>>
>>>>
>>>>
>>> No, I was thinking in the setup_cgroup() function in conf.c.
>>>
>>> Something like:
>>>
>>> ...
>>>
>>> if (!access("/var/lib/lxc/mycontainer/nsgroup/memory.meminfo"), F_OK) {
>>>  mount("/var/lib/lxc/mycontainer/nsgroup/memory.meminfo",
>>> "/proc/meminfo",
>>> MS_BIND, ...);
>>> }
>>>
>>> ...
>>>
>>>
>>> but a bit more clean :)
>>>
>>>
>>>
>>
>>
>> hmm... ok, got it, but don't know why does it won't work ;)
>>
>> @@ -999,12 +999,14 @@
>>  static int setup_cgroup(const char *name)
>>  {
>>     char filename[MAXPATHLEN];
>> +    char meminfofilename[MAXPATHLEN];
>>     char line[MAXPATHLEN];
>>     struct stat s;
>>     int ret;
>>
>>     snprintf(filename, MAXPATHLEN, LXCPATH "/%s/cgroup", name);
>> -
>> +    snprintf(meminfofilename, MAXPATHLEN, LXCPATH
>> "/%s/nsgroup/memory.meminfo", name);
>> +
>>     if (stat(filename, &s)) {
>>         SYSERROR("failed to stat '%s'", filename);
>>         return -1;
>> @@ -1024,6 +1026,10 @@
>>
>>     INFO("cgroup has been setup");
>>
>> +    /* mount memory.meminfo as /proc/meminfo */
>> +    if (!access(meminfofilename, F_OK)) {
>> +        mount(meminfofilename, "/proc/meminfo", "none", MS_BIND, 0);
>> +     }
>>     return 0;
>>  }
>>
>>
>> hmm... any idea Daniel? :)
>>
>>
> Yep, can you check the return code of the mount call and return an error ?
> if (mount(....)) {
>   SYSERROR("failed to mount '%s' to '/proc/meminfo'", meminfofilename);
>   return -1;
> }
> at least to verify if this does not fail.
> and maybe add an INFO trace if the mount is successful saying
> "/proc/meminfo" is setup with the cgroup.
>
> ps : you should launch the command with the "-l INFO" to see the message.
>


Weird. I made a test and move the mount the /proc/meminfo to the
setup_console() and it did not take effect. mount() did not fail (there were
no failed log).
Why I moved this part of code? Well.. I was wonder that what was happend if
I mount /proc/meminfo after the setup_mount() to override /proc/meminfo.
Don't have idea what can I do next ;) Daniel?

-- 
Krzysztof Taraszka
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