Re: [vserver] cgroups soon incompatible with Libvirt

From: Art -kwaak- van Breemen <ard_at_telegraafnet.nl>
Date: Fri 03 Jan 2014 - 14:39:59 GMT
Message-ID: <20140103143958.GO4689@telegraafnet.nl>

Hi,

On Tue, Dec 31, 2013 at 07:39:35PM +0000, Serge Victor wrote:
> The thing is kernel 3.4.x is properly enforcing it, killing the
> leaking process with OOM, but 3.10.x is probably doing something more,
> as you have suggested.

3.4 will eventually lockup too. Depending on the amounts of near
OOM situations you can cause. 3.10 can do it a bit faster :-).

> I still really do not know how far does it go, though. If I do not
> share the filesystem but one LVM2 VG, do you think it still may count?
The things I saw were related to ext4 write-actions needing to
have memory, going into some "I really need memory bad, go do
some freeing, meanwhile I stay locked", actually saying it is
eating memory from the wrong pool. I do not know if it is a per
filesystem lock or a per kernel lock. I would assume a per
filesystem lock though.

> How can we try to fix it? Because the whole idea of vserver cgroups is
> ruined, if it freezes the whole machine, is not it?
It's probably mainline memory cgroups.
I have a ticket (dated november) on my name here at work that
says I need to build a testcase, so I can make some bugreports.
Essence to trigger it is to be continously near OOM conditions in
the cgroup, while doing some writes and some writes in that same
cgroup. It will happen with 3.2+ but 3.10 will trigger much more
easily.
When I have less urgent matters I will make a good testcase.

There are more things wrong with cgroups in the kernel, like the
I/O throttle example: (see
https://www.kernel.org/doc/Documentation/cgroups/blkio-controller.txt
) it shows an example of doing I/O throttle using two cgroups on
a single filesystem on a single device.
I can tell you that the whole filesystem gets throttled depending
in whos cgroup it is performing.
Shared device throttling works as long as you don't share the
filesystems.

Regards,
Ard
Received on Fri Jan 3 14:40:04 2014

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