[PATCH][RFC] memory.min_usage again

Balbir Singh balbir at linux.vnet.ibm.com
Sun Sep 28 19:21:06 PDT 2008

YAMAMOTO Takashi wrote:
> hi,
>> On Wed, 10 Sep 2008 08:32:15 -0700
>> Balbir Singh <balbir at linux.vnet.ibm.com> wrote:
>>> YAMAMOTO Takashi wrote:
>>>> hi,
>>>>> hi,
>>>>> here's a patch to implement memory.min_usage,
>>>>> which controls the minimum memory usage for a cgroup.
>>>>> it works similarly to mlock;
>>>>> global memory reclamation doesn't reclaim memory from
>>>>> cgroups whose memory usage is below the value.
>>>>> setting it too high is a dangerous operation.
>>> Looking through the code I am a little worried, what if every cgroup is below
>>> minimum value and the system is under memory pressure, do we OOM, while we could
>>> have easily reclaimed?
> i'm not sure what you are worring about.  can you explain a little more?
> under the configuration, OOM is an expected behaviour.

Yes, but an OOM will violate the min_memory right? We promise not to reclaim,
but we can OOM. I would rather implement them as watermarks (best effort
service, rather than a guarantee). OOMing the system sounds bad, specially if
memory can be reclaimed.. No?

>>> I would prefer to see some heuristics around such a feature, mostly around the
>>> priority that do_try_to_free_pages() to determine how desperate we are for
>>> reclaiming memory.
>> Taking "priority" of memory reclaim path into account is good.
>> ==
>> static unsigned long shrink_inactive_list(unsigned long max_scan,
>>                         struct zone *zone, struct scan_control *sc,
>>                         int priority, int file)
>> ==
>> How about ignore min_usage if "priority < DEF_PRIORITY - 2" ?
> are you suggesting ignoring mlock etc as well in that case?

No.. not at all, we will get an mlock controller as well.

> YAMAMOTO Takashi


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