4-core slow due to disk access
Rashkae
ubuntu at tigershaunt.com
Mon Apr 26 18:20:07 UTC 2010
Joep L. Blom wrote:
> My outputs are:
> ~$ free
> total used free shared buffers cached
> Mem: 3992748 2895328 1097420 0 50168 847436
> -/+ buffers/cache: 1997724 1995024
> Swap: 8193108 889160 7303948
>
> and:
> Committed_AS: 3019596 kB
> VmallocTotal: 34359738367 kB
That looks like a comfortable load. Though I'm impressed at anyone
other than me who an drive a desktop to 3GB Allocated... :)
The amount of swap used still surprises me, but that might be due to
simple kernel tuning on the kernel version you are using.
My next suggestion would be to use some kind of swap monitor and watch
it while this disk activity is slowing you down, and see if you can
confirm if the system is hitting swap at those times. My personal
favorite is Gkrellm. It has nice visual charts that will often show you
at a glance what your bottleneck is. For something more old fashioned,
you can use vmstat (part of the sysstat package.).. The usual sign that
you are dealing with memory starvation is when the system has to swap
out and swap in (read / write to swap) at the same time. I believe that
to be an indication that you ran out of ram for the task at hand and
memory needs to be evicted from ram to make room for the pages being
requested. As a strictly rule of thumb, which is by no means scientific
and I'm sure would be greatly debated, I don't usually observe that
problem until Committed_AS: value exceeds physical RAM. If that is the
case, however, then it becomes a matter of finding out which process
exactly chewed up all that memory.
I see from your free that you have 800MB of swap used even though there
is still 1 GB of ram free, I suspect that a process was earlier taking
up all that memory which was then terminated (or crashed)
(PS, on most system, the Committed_AS: on a freshly started computer and
gnome desktop should be in the neighbourhood of 500MB)
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