(1) the 'dcache' system is stealing memory which it doesn't release;
effectively a memory leak,
(2) the 'dcache' system appears to include a method for aging the memory
it uses, presumably to allow it to be released, but this doesn't
appear to work quite right,
(3) there may be limits on the amount of leakage such that it is not
noticed on machines with more than 8 Mbyte of RAM,
I've included a small test script at the end of this message for people
who might like to see if their machine appears to be affected. Here's
the results for my machine:
$ ./test-compile.sh ~sys
Test gcc compile times.
Linux version 2.1.96 (root@lorentz) (gcc version 2.8.1) #46 Thu Apr 16 09:57:31 EST 1998
gcc takes 42.32 seconds before 'find'
find /home/sys -print | wc --> find took 25.42 seconds
15541 15541 630856
gcc takes 296.25 seconds after 'find'
find /home/sys -print | wc --> find took 24.48 seconds
15541 15541 630856
gcc takes 317.37 seconds after 120 second wait
Notice that the performance of the two runs of 'find' are almost identical,
indicating that it got negligible benefit from the caching. Also, there
is no apparent recovery of memory after a 2 minute wait.
My small testing script is below. It would be interesting to see if
a machine with more than 8 Mbyte RAM is affected. I conjecture that
a machine with 16 Mbyte would need to 'find' on a path with many
tens of thousands of files.
----------------------- Start of test script ---------------------------
#! /bin/bash
# W. Metzenthen billm@suburbia.net, billm@melbpc.org.au
#
# Rust tester.
# Call with a single parameter, a path containing lots of
# files and directories (?).
# e.g. /usr/src/linux has barely enough files (about 5000) to
# show much effect on an 8 Mbyte machine, but a path with
# 15000 files & directories gives pronounced results.
#
# I have more than one version of 'time' on my machine...
time=/usr/local/bin/time
if [ "$1" == "" ]
then
finddir=/
else
finddir="$1"
fi
echo "Test gcc compile times."
cat /proc/version
function timetest() {
# Do what a kernel compile does for one particular file...
$time --format="$1" \
gcc -D__KERNEL__ -I/usr/src/linux/include -Wall \
-Wstrict-prototypes -O2 -fomit-frame-pointer -pipe \
-fno-strength-reduce -m486 -DCPU=486 \
-c -o /tmp/icmp.o icmp.c \
2>&1
}
cd /usr/src/linux/net/ipv4
timetest "gcc takes %e seconds before 'find'"
echo -n "find $finddir -print | wc --> "
($time --format="find took %e seconds" find $finddir -print | wc) 2>&1
timetest "gcc takes %e seconds after 'find'"
echo -n "find $finddir -print | wc --> "
($time --format="find took %e seconds" find $finddir -print | wc) 2>&1
sleep 120
timetest "gcc takes %e seconds after 120 second wait"
---------------------------- End of script -----------------------------
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