memory mgmt/tuning for diskless machines

memory mgmt/tuning for diskless machines

[David L. Parsley]

Hi,

I'm working on a project for building diskless multimedia terminals/game
consoles.  One issue I'm having is my terminal seems to go OOM and crash
from time to time.  It's strange, I would expect the OOM killer to blow
away X, but it doesn't - the machine just becomes unresponsive.

Since this is a quasi-embedded platform, what I'd REALLY like to do is
tune the vm so mallocs fail when freepages falls below a certain point. 
I'm using cramfs, and what I suspect is happening is that once memory
gets too low, the kernel doesn't have enough memory to uncompress
pages.  Since there's no swap, there's nothing to page out.

So... it occured to me I could tune this with /proc/sys/vm/freepages -
but now I find that it's read-only, and I can't echo x y z > freepages
like I used to.  What's up with that?

Suggestions?

regards,
	David
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David L. Parsley
Network Administrator
Roanoke College
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Re: memory mgmt/tuning for diskless machines

[Rik van Riel]

On Mon, 26 Mar 2001, David L. Parsley wrote:

> I'm working on a project for building diskless multimedia terminals/game
> consoles.  One issue I'm having is my terminal seems to go OOM and crash
> from time to time.  It's strange, I would expect the OOM killer to blow
> away X, but it doesn't - the machine just becomes unresponsive.
> 
> Since this is a quasi-embedded platform, what I'd REALLY like to do is
> tune the vm so mallocs fail when freepages falls below a certain point. 

Hi David,

I think you might want to talk with Jonathan Morton about
your situation. Jonathan is working on a non-overcommit
patch which will make sure no more memory is malloc()ed
than what is available.

Chances are this patch will stay separate for the kernel
for some more time and get integrated later when it is
well-tested and there is a certain userbase who really
want/need the patch (I suspect both of these will happen
rather soon, though;)).

regards,

Rik
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However, without VM there's truly nothing to lose...

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Re: memory mgmt/tuning for diskless machines

[David L. Parsley]

Rik van Riel wrote:
> 
> On Mon, 26 Mar 2001, David L. Parsley wrote:
> 
> > I'm working on a project for building diskless multimedia terminals/game
> > consoles.  One issue I'm having is my terminal seems to go OOM and crash
> > from time to time.  It's strange, I would expect the OOM killer to blow
> > away X, but it doesn't - the machine just becomes unresponsive.
> >
> > Since this is a quasi-embedded platform, what I'd REALLY like to do is
> > tune the vm so mallocs fail when freepages falls below a certain point.
> 
> Hi David,
> 
> I think you might want to talk with Jonathan Morton about
> your situation. Jonathan is working on a non-overcommit
> patch which will make sure no more memory is malloc()ed
> than what is available.

Thanks Rick, I'll bet you're right.  I changed the sysctl registration
to make /proc/sys/vm/freepages read-write, and even playing with it for
a while it was a no-win.  Either 1) the machine would become
unresponsive, or 2) X would crash.  For embedded systems, the
non-over-commit patch is almost certainly the way to go - and we all
know how popular embedded Linux is these days. ;-)

I'll try to search for his patch in kernel archives and let you know how
it works out.

Jonathan - if you could ship me the patch I'd appreciate it, but I'll
try searching first.

regards,
	David

-- 
David L. Parsley
Network Administrator
Roanoke College
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Re: memory mgmt/tuning for diskless machines

[Jonathan Morton]

>I'll try to search for his patch in kernel archives and let you know how
>it works out.
>
>Jonathan - if you could ship me the patch I'd appreciate it, but I'll
>try searching first.

Search the last few days for a post beginning "[TAKE3] [PATCH]"...

Note there is a bug in the accounting which appears to be able to cause the
count of reserved memory to go negative under some circumstances.  I
triggered it by starting 4 copies of the Blackdown Java 1.2.2 VM, then
closing them.  With the patch enabled, two extra fields appear in
/proc/meminfo for monitoring.

Note also that I'm not sbscribed on the linux-mm list (perhaps I should
be), so please CC me.

--------------------------------------------------------------
from:     Jonathan "Chromatix" Morton
mail:     chromi@cyberspace.org  (not for attachments)
big-mail: chromatix@penguinpowered.com
uni-mail: j.d.morton@lancaster.ac.uk

The key to knowledge is not to rely on people to teach you it.

Get VNC Server for Macintosh from http://www.chromatix.uklinux.net/vnc/

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Re: memory mgmt/tuning for diskless machines

[Marcelo Tosatti]

On Mon, 26 Mar 2001, David L. Parsley wrote:

> Hi,
> 
> I'm working on a project for building diskless multimedia terminals/game
> consoles.  One issue I'm having is my terminal seems to go OOM and crash
> from time to time.  It's strange, I would expect the OOM killer to blow
> away X, but it doesn't - the machine just becomes unresponsive.
> 
> Since this is a quasi-embedded platform, what I'd REALLY like to do is
> tune the vm so mallocs fail when freepages falls below a certain point. 
> I'm using cramfs, and what I suspect is happening is that once memory
> gets too low, the kernel doesn't have enough memory to uncompress
> pages.  Since there's no swap, there's nothing to page out.
> 
> So... it occured to me I could tune this with /proc/sys/vm/freepages -
> but now I find that it's read-only, and I can't echo x y z > freepages
> like I used to.  What's up with that?

It should work. Are you sure you're trying to change it as root ? 

> Suggestions?

Which kernel version are you using ? 

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Re: memory mgmt/tuning for diskless machines

[Szabolcs Szakacsits]

On Mon, 2 Apr 2001, Marcelo Tosatti wrote:

> > So... it occured to me I could tune this with /proc/sys/vm/freepages -
> > but now I find that it's read-only,
> It should work. Are you sure you're trying to change it as root ?
> Which kernel version are you using ?

It doesn't work since 2.4.0-test9
	http://www.uwsg.iu.edu/hypermail/linux/kernel/0009.2/0129.html

    Szaka

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