[uml-devel] uml crashes when producing large files

[uml-devel] uml crashes when producing large files

[Herbert Volkmann]

Hi List,

i ran in the following problem:
when i produce files (with dd) or copy files to or from the uml machine,
i can see (with top), that the used memory and the cached things
increases, while the unused memory will go down. shortly before memory
will come to zero, the uml stops working completely without any messages
in the /var/log/* files on uml or host system.

if i do in between a "echo 3 > /proc/sys/vm/drop_caches"

it cleans caches, frees memory and works fine! but i have to do this all
10 seconds when i use dd for producing large files ;-(

these are the components i use:
- debian etch on host with debian kernel patched with skas3 from debian 
- 1024 MB RAM on host
- RAID5 System with 3ware Controller (5x2G) almost 1 TB
- on uml i use debian etch, with bridged networking, 512MB RAM for uml
- 6G root_fs for uml and 256M swap

here is the command with which i start the uml:
sudo -u uml /usr/bin/linux.uml umid=uml mem=512M eth0=tuntap,tap1
ubd0=/usr/media/uml-linux/root_fs_2007_04_23
ubd1=/usr/media/uml-linux/swap_fs con=null root=/dev/ubda uml_dir=/tmp/

I would be really happy if someone could tell me what i can test more to
find out why this system is instable with i/o operations and caches.

thanx for any reply,
Herbert


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Re: [uml-devel] uml crashes when producing large files

[Blaisorblade]

On giovedì 26 aprile 2007, Herbert Volkmann wrote:
> Hi List,
>
> i ran in the following problem:
Very strange...
> when i produce files (with dd) or copy files to or from the uml machine,
Which filesystems are involved? Can you give a sample command?

> i can see (with top),
Run on the guest (i.e. UML) I guess, right?
> that the used memory and the cached things 
> increases, while the unused memory will go down.
That is reasonable, but the cache should not make the system stop.
> shortly before memory 
> will come to zero, the uml stops working completely without any messages
> in the /var/log/* files on uml or host system.
>
> if i do in between a "echo 3 > /proc/sys/vm/drop_caches"
On the guest (i.e. UML) I assume, right?
>
> it cleans caches, frees memory and works fine! but i have to do this all
> 10 seconds when i use dd for producing large files ;-(
>
> these are the components i use:
> - debian etch on host with debian kernel patched with skas3 from debian
32bit system, right?
> - 1024 MB RAM on host
> - RAID5 System with 3ware Controller (5x2G) almost 1 TB
> - on uml i use debian etch, with bridged networking, 512MB RAM for uml
Which UML kernel release? That's the most important thing.
> - 6G root_fs for uml and 256M swap
>
> here is the command with which i start the uml:
> sudo -u uml /usr/bin/linux.uml umid=uml mem=512M eth0=tuntap,tap1
> ubd0=/usr/media/uml-linux/root_fs_2007_04_23
> ubd1=/usr/media/uml-linux/swap_fs con=null root=/dev/ubda uml_dir=/tmp/
>
> I would be really happy if someone could tell me what i can test more to
> find out why this system is instable with i/o operations and caches.

I have only a doubt: if you are filling a shmfs/tmpfs filesystem (which is 
backed by ram), that's an almost normal behaviour, and can happen even on 
host systems.

> thanx for any reply,
> Herbert

-- 
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade

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