OOM-killer prevention for master kdeinit process

[Robert Knight]

> PS: Just in case somebody wonders why I hate OOM handling on Linux so much
> then the answer is that my 1G RAM work machine with no swap at all being
> trashed to death is probably the top reason why I reboot it (not that I
> reboot that often otherwise).

What on earth is using up that 1GB?

Regards,
Robert.

On 02/08/06, Lubos Lunak <l.lunak at suse.cz> wrote:
>
>  Hello,
>
>  short summary: Out Of Memory handling on Linux sucks, KDE can suffer badly
> from it, kernel devels are unable to do anything about it, so let's again
> work around things ourselves.
>
>  Reading for this is
> http://www.lugroma.org/contenuti/eventi/LinuxDay2005/atti/Arcangeli-MemoryManagementKernel26.pdf .
> Only pages 8-11 are relevant, pages after that are unrelated, pages before
> that are either not really interesting or not true as long as KDE is
> concerned - somehow I get the impression that OOM-handling is worse and worse
> as the time goes (ah, and yes, I really hate it, just in case that's not
> obvious). Anyway, to the point:
>
>  Run this:
>
> ls /proc/*/oom_score | grep -v self | sed 's/\(.*\)\/\(.*\)/echo -n "\1 ";
> echo -n "`cat \1\/\2 2>\/dev\/null` "; readlink \1\/exe || echo/'| sh |
> sort -nr +1
>
> That gives lines with </proc/pid> <likelyhood to be oom-killed> <binary>.
> Run "pstree -p" and compare it with the top of the list. The very first item
> that's going to be killed when running out of memory is going to be the
> master kdeinit process, i.e. the tiny thingy that is linked against our basic
> libraries which we use for launching apps. The reason why it's going to be
> killed the first is that OOM-killing has some "smart" heuristic that counts
> also all child processes into parent's score (it's mentioned in the paper)
> and since this process launches almost all KDE processes it gets the sum of
> almost whole KDE. No wonder it almost always wins the first place in the
> list. In fact, since the killing first kills all children of the "offending"
> process, that means that before memory is reclaimed to get out of OOM,
> various processes like klauncher or kwin are killed -> KDE is pretty
> unusable.
>
>  We've already tried to make kernel developers turn that off, change it in
> order not to cause this kdeinit problem or at least give a better way to
> exclude kdeinit than to echo as root to somewhere in /proc, to no avail
> (because a good OOM-killer is apparently nothing trivial and also because
> kernel developers have funny ideas about userspace). So we somewhere need to
> do something like "echo -10 > /proc/<pid_of_kdeinit>/oom_adjust" as root when
> running on Linux ( -10 means the score will be multiplied by 2^-10, i.e.
> divided by 1024 ; given that kdeinit is very unlikely to go haywire that
> seems pretty safe).
>
>  Now, who's the setuid guru here :)? Is the attached (KDE3) patch ok? I'd
> prefer not to have security people going after me. The setuid stuff is copied
> from artswrapper, the privileges are dropped immediately so I hope there's no
> problem.
>
>
> PS: Just in case somebody wonders why I hate OOM handling on Linux so much
> then the answer is that my 1G RAM work machine with no swap at all being
> trashed to death is probably the top reason why I reboot it (not that I
> reboot that often otherwise).
>
> --
> Lubos Lunak
> KDE developer
> ---------------------------------------------------------------------
> SuSE CR, s.r.o.  e-mail: l.lunak at suse.cz , l.lunak at kde.org
> Drahobejlova 27  tel: +420 2 9654 2373
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> Czech Republic   http://www.suse.cz/
>
>
>