Re: Setting oom_adj on linux?

Magnus Hagander wrote:
> On Mon, Jan 4, 2010 at 17:07, Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:
>
>> Magnus Hagander wrote:
>>
>>> On Mon, Jan 4, 2010 at 16:45, Alvaro Herrera <alvherre(at)commandprompt(dot)com>
>>> wrote:
>>>
>>>
>>>> Magnus Hagander wrote:
>>>>
>>>>
>>>>> I realize this is a very platform-specific thing, but should we
>>>>> consider setting the value of /proc/<pid>/oom_adj when running on
>>>>> linux? See:
>>>>>
>>>>>
>>>> http://archives.postgresql.org/message-id/20080201223336.GC24780%40alvh.no-ip.org
>>>>
>>>>
>>> Grr. I had zero recollectoin of that :S
>>>
>>> Can't find a useful consensus though?
>>>
>>>
>>>
>> It is probably worth trying to protect the postmaster in the init script.
>> Beyond that things probably start to get fairly difficult.
>>
>
> Right. But AFAICS (though I haven't tested with -17), it will become
> inherited to children, which is something we'd want to *undo*, no?
>

[experiments]

Yes, darnit, you're right. But it looks like the oom_adj file can be set
to the default by the process owner:

[andrew(at)sophia ~]$ ls -l /proc/6520/oom_adj
-rw-r--r-- 1 andrew andrew 0 2010-01-04 12:37 /proc/6520/oom_adj
[andrew(at)sophia ~]$ cat /proc/6520/oom_adj
0
[andrew(at)sophia ~]$ id
uid=500(andrew) gid=500(andrew) groups=10(wheel),500(andrew)
[andrew(at)sophia ~]$ echo -17 > /proc/6520/oom_adj
-bash: echo: write error: Permission denied
[andrew(at)sophia ~]$ echo 0 > /proc/6520/oom_adj
[andrew(at)sophia ~]$ echo -17 > /proc/6520/oom_adj
-bash: echo: write error: Permission denied
[andrew(at)sophia ~]$

But that would be a pain to have to do.

OTOH, disabling the OOM killer is not always an option. I recently tried
it on one system and had to revert it rapidly because the system stopped
working in minutes. Some software just doesn't live well in such
environments, sadly.

cheers

andrew