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

["Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>]

> Can't vm_committed_space grow *bigger* than available memory 
> when using
> swap? It may indicate the 'static' demand for memory (in 
> terms of requested
> allocations so far) but we're interested in dynamic demand 
> (how much of that
> allocated memory is actually used), which afaics 
> vm_committed_space doesn't
> appear very useful for.
> 
> Some indication of paging churn, or average age of pages in memory, or
> something like that, would seem more useful (albeit 
> arbitrarily harder to
> work out from within the balloon driver!).
> 
> Maybe I'm missing something. I've only had a quick look at usage of
> vm_committed_space.

You are right about vm_committed_space growing bigger.  I was
too terse: I was trying to use it in a min(x,y,z) calculation
with the existing algorithm, but apparently it becomes too small
sometimes (e.g. during shutdown) and I observed OOM problems.

However vm_committed_space seems to be a pretty good dynamic demand
indicator in general.  Try watch'ing it in a window while doing
other tasks on a machine/VM, e.g.:

watch grep Committed_AS /proc/meminfo

It grows rapidly when memory hogs are launched and shrinks
rapidly when the machine goes idle.  So it seems to work
well for at least a first approximation for selfballooning.

Dan


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