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SubjectRe: DOS by unprivileged user
On Sun 22-04-18 10:43:00, vcaputo@pengaru.com wrote:
> On Sun, Apr 22, 2018 at 12:16:54PM +0200, Pavel Machek wrote:
> > On Thu 2018-04-19 21:13:35, Ferry Toth wrote:
> > > It appears any ordinary user can easily create a DOS on linux.
> > >
> > > One sure way to reproduce this is to open gitk on the linux kernel repo
> > > (SIC) on a machine with 8GB RAM 16 GB swap on a HDD with btrfs and quad core
> > > + hyperthreading. But I will be easy enough to get the same effect with more
> > > RAM, other fs etc.
> >
> > You may want to disable swap.
> >
>
> I run without swap on my laptops, and still observe long periods of
> thrashing on the road towards OOM. What seems to occur is the active
> file-backed mappings of executables/libraries become a sort of swap
> area, repeatedly being discarded and faulted back in as the context
> switches occur.
>
> If there's any good way to prevent this, I'd like to know.

I am afraid there is none yet. Johannes had some ground work for
page cache trashing detection https://marc.info/?i=20170727153010.23347-1-hannes%40cmpxchg.org
but there was no version of the patchseries for quite some time and
there was no integration into the oom detection which would be
non-trivial as well.

I realize this sucks. But the reality is that this is far from trivial
to resolve without introducing pre-mature OOM killer invocations.
--
Michal Hocko
SUSE Labs

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