[TriLUG] file copy flushing memory

[Joseph Mack NA3T]

On Fri, 2 Dec 2005, Rick DeNatale wrote:

don't have "swapiness". I'm on a 2.4 machine, maybe 
swapiness is a 2.6ism

> You might be able to use the bash built-in command ulimit

This didn't help but it was an interesting enough idea that 
it was worth testing.

Test: time to download a 10M webpage from a machine on the 
same (quiet) network. These bytes will not touch the local 
disk and will only go through the network drivers and memory 
presumably staying in memory unless flushed by some other 
process. Then copy CD iso's (these being bigger than the 
machine's memory of 192M) from one local disk to another, 
and retime the webpage dowload after an iso's worth of 
copying.

time to copy 10M of files     cp process

35-40 sec                     none
53-55 sec                     unlimited cp
53-55 sec                     ulimit -m 20480
                               (ie 20M working set) 
53-55 sec                     ulimit -v 20480
                               (ie 20M swap)


I tried the ulimit -v commands first and found that if the 
size was small enough I couldn't load bash (killed) or man 
bash (killed). On finding no effect on the copy with -v 
20480, I realised that the machine wasn't swapping anyhow 
and I was barking up the wrong tree. Looking at man ulimit 
again, I decided I really wanted -m. Still changing -m from 
unlimited to 20M didn't affect the problem.

Neat idea though ;-)

Joe
-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
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