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#!/bin/sh
[ -x /sbin/blockdev ] || exit $NA
# more readahead = (hopefully) less hard drive activity.
# less readahead = less trashing the page cache.
DRIVE_READAHEAD_AC=${DRIVE_READAHEAD_AC:-256}
DRIVE_READAHEAD_BAT=${DRIVE_READAHEAD_BAT:-3072}
help() {
cat <<EOF
--------
$0: Control drive readahead.
This hook tries to trade off the number of times we spin up a drive
to read for potentially wasted cache.
Drive readahead parameters:
DRIVE_READAHEAD_AC = Number of KB to speculatively read on AC.
Defaults to 256 KB.
DRIVE_READAHEAD_BAT = Number of KB to speculatively read on battery.
Defaults to 3072 KB.
EOF
}
readahead() {
# the intent here is to iterate through all filesystems
# mounted on a local block device. It Works For The Maintainer(tm).
# More sophistication in figuring out what exactly is a local block device
# would be welcome.
for dev in $(awk '/^\/dev\// {print $1}'</etc/mtab); do
/sbin/blockdev --setfra $1 "$dev"
done
}
case $1 in
true) readahead "$DRIVE_READAHEAD_BAT" ;;
false) readahead "$DRIVE_READAHEAD_AC" ;;
help) help;;
*) exit $NA ;;
esac
exit 0
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