BOINC Q&A -- 13/10/06

Advanced Memory Management, what is the idea/aim behind that?

Well that is a good question, the advanced memory management is more about setting boundary conditions on how much BOINC and related processes are allowed to use.

We still get a few reports of BOINC causing systems to become unresponsive or sluggish. Most of the investigations we have done revealed a machine that was paging a lot during the times BOINC was running. Paging is the process the OS uses to free up less frequently used memory to make room for active tasks by writing those pages of memory to disk. Each page of memory is roughly 4KB in size on a x86 processor.

So lets say you are running a machine with 512MB's of memory. Windows XP uses roughly 128MB of that on boot-up and will allow parts of itself to be paged out to disk. The last round of virus scanners I looked at want around 100MB of memory, the little system tray icons in the lower right part of your screen generally take about 5MB a piece, with the notable exception of the various IM clients which have bloated out to 20-60MB a piece. Any additional programs running on your machine such as a web browser or email client can take anywhere from 20MB up to 100MB.

When the OS comes under memory pressure it starts looking for chunks of memory that haven't been touched in awhile and writes them out to disk and then loads something into that chunk of memory that is more relevant.

So let us say that you are attached to Rosetta@Home and you walk away from your computer for an hour or so, during that time Rosetta@Home has used over 256MBs of memory continuously for at least 30 minutes and the OS has had to page a lot of stuff to make room for it, including itself. You start menu has to be reread from disk or whichever application you happen to be using before you left. All of that paging takes a few moments and makes your computer feel really really slow.

With the introduction of this feature we hope we can finally close one of the last remaining loopholes to user responsiveness.

Right now we have the following two settings planned:

1. Percentage of memory use while user is active.
2. Percentage of memory use while user is idle.

What should happen is that BOINC will detect how much memory is installed on the machine, and every 10 seconds or so looks at how much memory a science application is using. If a science application exceeds the total allotment BOINC will shut it down and look for another application to schedule.

I'm really looking forward to this feature since my 2GB machine uses about 1.2GB of memory without BOINC even running and I have four processors to feed. Up until the middle of last year I only had 1GB in my machine and if I had BOINC running it was pretty painful when BOINC rescheduled all the science applications on the machine while I was working.