Comment 298 for bug 131094

Just to add my recent observations.

I turned swap off because I felt that 4GB main memory is plenty of space. Machine was working ok but during the day, without even doing anything special, just typing along, browsing a little, and opening some windows, but not starting programs, the machine started to block. X was unresponsive up to 15 minutes, atop displayed heavy page scanning, and the load factor went up to 8. Disk was very active. Interestingly, there is always plenty of free physical memory available. Cache up to 1 GB and 512mb free or even more. So no reason to do anything with memory pages at all.

This repeats over and over again. Sometimes just for a minute, sometimes for two. No fixed time periods, no fixed recurrence pattern. But it is always the same picture, load goes up, page scanning starts, IO is heavy (no swap configured) - maybe in a different order.

Was checking /var/log/messages during this and without swap, I got memory allocation failures messages from pulseaudio. Scanning and disk activity seem to start at this point in time. With swap added, these allocation failures are gone, but the overall behavior is the same. So I guess that an allocation failure of some kind (no messages), causes the rescanning of all pages and therefore the heavy disk activity.

I noticed, that committed virtual memory is of course bigger than the available real memory. Some programs, such as nautilus have a virtual size of up to 700mb while physical memory usage is around 60mb. Firefox virtual around 1gb, real 200mb... skype 200 to 30mb. Just to add my recent observations.

I turned swap off because I felt that 4GB main memory is plenty of space. Machine was working ok but during the day, without even doing anything special, just typing along, browsing a little, and opening some windows, but not starting programs, the machine started to block. X was unresponsive up to 15 minutes, atop displayed heavy page scanning, and the load factor went up to 8. Disk was very active. Interestingly, there is still plenty of free physical memory available. Cache up to 1 GB and 512mb free or even more. So no reason to do anything with pages at all.

This repeats over and over again. Sometimes just for a minute, sometimes for two. No fixed time periods. But it is always the same picture, load goes up, page scanning starts, IO is heavy (no swap configured). Maybe the order of events is different, but because all programs seem to halt for a moment, not all information can be seen.

I noticed, that committed virtual memory is of course bigger than the available real memory. Some programs, such as nautilus have a virtual size of up to 700mb while physical memory usage is around 60mb. Firefox virtual around 1gb, real 200mb... skype 200 to 30mb.

I understand that virtual size is bigger, but it seems to the sum of all virtual sizes going over the limit of the physical memory, causes very frequent and hefty memory page scans. Strange is, that without swap, the disk is used heavily. I am not an expert, but I assume that this is related to relocating/dropping program code that was mapped into virtual memory.

Only observations. Now, I updated my BIOS and bought a new harddisk. Will check if this changes anything. But I doubt that.

Running Ubuntu 9.10 with 2.6.33 on a Lenovo T500, 4GB memory.
Linux mymachine 2.6.33-020633-generic #020633 SMP Thu Feb 25 10:10:03 UTC 2010 x86_64 GNU/Linux