#!/bin/sh

. "${PM_FUNCTIONS}"

VM="/proc/sys/vm"
vmfiles="laptop_mode dirty_ratio dirty_background_ratio 
         dirty_writeback_centisecs"

LAPTOP_MODE=${LAPTOP_MODE:-5}
LAPTOP_DIRTY_RATIO=${LAPTOP_DIRTY_RATIO:-60}
LAPTOP_DIRTY_BG_RATIO=${LAPTOP_DIRTY_BG_RATIO:-40}
LAPTOP_DIRTY_WRITEBACK=${LAPTOP_DIRTY_WRITEBACK:-60000}

help() {
    cat <<EOF
--------
$0: Laptop mode tuning parameters.
This hook controls how agressive the system is at trying to avoid
writing to disk.  The longer the disk is idle, the more power you can save.

This hook is only active on battery power, and it restores these values
to kernel defaults when on AC power.

It has 4 tuneable parameters: 
LAPTOP_MODE = value for laptop_mode on battery.
Defaults to 5, which enables laptop mode and forces the system to wait 
5 seconds whenever something asks to write to disk to flush out as much
data as we can.

LAPTOP_DIRTY_RATIO = the ratio of dirty memory to all memory that 
processes start doing their own writeout.  
Defaults to 60, which means that the kernel will not start forcing process
to write out file information that has been changed but not saved until 60%
of usable system memory is filled with dirty information.

LAPTOP_DIRTY_BG_RATIO = The ratio of dirty memory to all memory that 
pdflush will wake up and start writing to disk.  
Defaults to 40, which means that the kernel will wake up a helper process
to try and write out dirty memory once 40% of usable system memory is dirty.

LAPTOP_DIRTY_WRITEBACK = The number of centiseconds between periodic
wakeups of the pdflush daemons.  
Defaults to 60000 (10 minutes), which menas that the kernel will flush dirty
memory every 10 minutes if dirty memory never hits 40% of system memory.

EOF
}

[ -w $VM/laptop_mode -a -w $VM/dirty_ratio ] || exit $NA

read_values() {
    for f in $vmfiles; do
	[ -r "$VM/$f" ] && cat "$VM/$f" || echo 0
    done
}

write_values() {
    for f in $vmfiles; do
	[ -w "$VM/$f" ] && echo $1 > "$VM/$f"
	shift
    done
}

laptop_mode_ac() {
    # disable laptop mode, set vm parameters back to sane defaults
    if state_exists laptop_mode_default; then
	write_values $(restorestate laptop_mode_default)
    else
	write_values 0 10 5 500
    fi	
    echo "Laptop mode disabled."
}

laptop_mode_battery() {
    # enable laptop mode, set vm parameters to buffer as many writes as 
    # possible.
    state_exists laptop_mode_default || \
	read_values | savestate laptop_mode_default
    write_values "$LAPTOP_MODE" "$LAPTOP_DIRTY_RATIO" \
	"$LAPTOP_DIRTY_BG_RATIO" "$LAPTOP_DIRTY_WRITEBACK"
    echo "Laptop mode enabled."
}

case $1 in
    true) laptop_mode_battery ;;
    false) laptop_mode_ac ;;
    help) help;;
    *) exit $NA ;;
esac

exit 0