Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19

Andrew Morton
2005-11-04T04:52:35Z

Badari Pulavarty <pbadari@gmail.com> wrote:
>
> > With Badari's patch and UML memory hotplug, the infrastructure is
> > there to make this work. The one thing I'm puzzling over right now is
> > how to measure memory pressure.
>
> Yep. This is the exactly the issue other product groups normally raise
> on Linux. How do we measure memory pressure in linux ? Some of our
> software products want to grow or shrink their memory usage depending
> on the memory pressure in the system. Since most memory is used for
> cache, "free" really doesn't indicate anything -they are monitoring
> info in /proc/meminfo and swapping rates to "guess" on the memory
> pressure. They want a clear way of finding out "how badly" system
> is under memory pressure. (As a starting point, they want to find out
> out of "cached" memory - how much is really easily "reclaimable"
> under memory pressure - without swapping). I know this is kind of
> crazy, but interesting to think about :)

Similarly, that SGI patch which was rejected 6-12 months ago to kill off
processes once they started swapping. We thought that it could be done
from userspace, but we need a way for userspace to detect when a task is
being swapped on a per-task basis.

I'm thinking a few numbers in the mm_struct, incremented in the pageout
code, reported via /proc/stat.