Re: [Xen-devel] [PATCH] linux/balloon: don't allow ballooningdowna domain below a reasonable limit

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 1/5/08 17:59, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> It doesn't measure memory or total virtual commitment.
> 
> Hmm... in my experiments, it seems to do exactly that.
> I wrote a simple "eatmem" program that uses a random
> amount of memory (writing to the first byte in each page)
> for a random amount of time (printing out the random values),
> and watched Committed_AS in /proc/meminfo and it seems
> to track well.

This makes sense since it does track swap commitment, and the pages your
program allocates are anonymous and hence would be backed by swap.

But still it seems to me there is a different between memory commitment and
dynamic memory pressure. And I would say that ballooning should be
influenced by the latter. For example, if your program allocates a random
amount of memory and dirties it all once, that ultimately will take up swap
space long term but it doesn't increase memory pressure unless the pages are
in active use by your application. What matters is the collective working
set across processes.

It might be the case though that, in practice, vm_committed_space is a
reasonable predictor for working set for some common types of workload. Many
applications probably keep their heaps fairly warm and hence in main memory.

 -- Keir



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel