Re: System freezes when RAM is full (64-bit)

[Michal Hocko <mhocko@suse.cz>]

On Fri 12-04-13 14:38:00, Ivan Danov wrote:
> On 12/04/13 13:11, Michal Hocko wrote:
> >On Fri 12-04-13 12:49:30, Ivan Danov wrote:
> >>$ cat /proc/sys/vm/swappiness
> >>60
> >OK, thanks for confirming this. It is really strange that we do not swap
> >almost at all, then.
> >>I have increased my swap partition from nearly 2GB to around 16GB,
> >>but the problem remains.
> >Increasing the swap partition will not help much as it almost unused
> >with 2G already (at least last data shown that).
> >
> >>Here I attach the logs for the larger swap partition. I use a MATLAB
> >>script to simulate the problem, but it also works in Octave:
> >>X = ones(100000,10000);
> >AFAIU this will create a matrix with 10^9 elements and initialize them
> >to 1. I am not familiar with octave but do you happen to know what is
> >the data type used for the element? 8B? It would be also interesting to
> >know how is the matrix organized and initialized. Does it fit into
> >memory at all?
> Yes, 8B each, so it will be almost 8GB and it should fit into the
> memory.

It won't fit in because kernel and other processes consume some memory
as well. So you have to swap.

> I don't know details how it actually works, but if it cannot
> create the matrix, MATLAB complains about that. Since it starts
> complaining even after 2000 more in the second dimension, maybe it
> needs the RAM to create it all. However on the desktop machine, both
> RAM and swap are being used (quite a lot of them both).

How much you swap depends on vm.swappiness. I would suggest increasing
the value if your workload is really so anononymous memory based.
Otherwise a lot of file pages are reclaimed which can lead to problems
you are seeing.

> >>I have tried to simulate the problem on a desktop installation with
> >>4GB of RAM, 10GB of swap partition, installed Ubuntu Lucid and then
> >>upgraded to 12.04, the problem isn't there, but the input is still
> >>quite choppy during the load. After the script finishes, everything
> >>looks fine. For the desktop installation the hard drive is not an
> >>SSD hard drive.
> >What is the kernel version used here?
> $ uname -a
> Linux ivan 3.2.0-40-generic #64-Ubuntu SMP Mon Mar 25 21:22:10 UTC
> 2013 x86_64 x86_64 x86_64 GNU/Linux

Is there any chance you could test with the latest vanilla kernel and 
Mel's patches from https://lkml.org/lkml/2013/4/11/516 on top?

[...]
-- 
Michal Hocko
SUSE Labs

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