On 4/23/2012 9:28 PM, Gustavo R Leal wrote:
I believe I've found the solution to excessive swapping with 1GB of memory.
There is a script "/usr/lib/pm-utils/power.d/laptop-mode" that is setting too
low values to VM tunable kernel parameters when on AC power:
dirty_background_ratio=5
dirty_ratio=10
The line 69 of the script is the following:
write_values 0 10 5 500
Changing the line with these values resulted in being able to run the system
with 1GB without swap partition and good performance even with many large
processes running.
write_values 0 90 20 500
This sets the VM subsystem with these values:
dirty_background_ratio=20
dirty_ratio=90
That makes the dirty_ratio even higher than when on battery. The
purpose of tuning these is to allow a laptop on battery to be more
aggressive about keeping dirty pages in the cache and letting the disk
stay asleep. Normally you want dirty pages to be flushed to disk fairly
quickly.
I'm curious if the normal value of 5 for background ratio but just
increasing dirty_ratio to 20 or 25 would have a similar effect on your
performance trouble without going to an excess.
Also if anything, increasing dirty_ratio should make swapping worse, not
better, since more ram will be tied up in dirty cache pages. Are you
sure you have a problem with swapping and not just applications blocking
while writing data to disk?
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