[Bug 131094] Re: Heavy Disk I/O harms desktop responsiveness

[ReneS]

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

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Heavy Disk I/O harms desktop responsiveness
https://bugs.launchpad.net/bugs/131094
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