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dmsquash: Add rd.live.overlay.thin 

This option changes the underlying mechanism for the overlay in the
dmsquash module.
Instead of a plain dm snapshot a dm thin snapshot is used. The advantage
of the thin snapshot is, that the TRIM command is recognized, which
means that at runtime, only the occupied blocks will be claimed from
memory, and freed blocks will really be freed in ram.

Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>
master
Fabian Deutsch 2015-02-18 14:31:40 +01:00 committed by Harald Hoyer
parent 7075a402d7
commit d6e34d362a
2 changed files with 33 additions and 1 deletions
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7
dracut.cmdline.7.asc
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@ -834,6 +834,13 @@ Enables debug output from the live boot process.
Specifies the directory within the squashfs where the ext3fs.img or rootfs.img
can be found. By default, this is __LiveOS__.

**rd.live.overlay.thin=**1::
Enables the usage of thin snapshots instead of classic dm snapshots.
The advantage of thin snapshots is, that they support discards, and will free
blocks which are not claimed by the filesystem. In this use case this means,
that memory is given back to the kernel, when the filesystem does not claim it
anymore.

**rd.writable.fsimg=**1::
Enables writable filesystem support. The system will boot with a fully
writable filesystem without snapshots __(see notes above about available live boot options)__.

27
modules.d/90dmsquash-live/dmsquash-live-root.sh
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@ -30,6 +30,8 @@ getargbool 0 rd.writable.fsimg -d -y writable_fsimg && writable_fsimg="yes"
overlay_size=$(getarg rd.live.overlay.size=)
[ -z "$overlay_size" ] && overlay_size=512

getargbool 0 rd.live.overlay.thin && thin_snapshot="yes"

# CD/DVD media check
[ -b $livedev ] && fs=$(blkid -s TYPE -o value $livedev)
if [ "$fs" = "iso9660" -o "$fs" = "udf" ]; then
@ -146,7 +148,30 @@ do_live_overlay() {
base=$BASE_LOOPDEV
over=$OVERLAY_LOOPDEV
fi
echo 0 $sz snapshot $base $over p 8 | dmsetup create live-rw
if [ -n "$thin_snapshot" ]; then
modprobe dm_thin_pool
mkdir /run/initramfs/thin-overlay

# In block units (512b)
thin_data_sz=$(( $overlay_size * 1024 * 1024 / 512 ))
thin_meta_sz=$(( $thin_data_sz / 10 ))

# It is important to have the backing file on a tmpfs
# this is needed to let the loopdevice support TRIM
dd if=/dev/null of=/run/initramfs/thin-overlay/meta bs=1b count=1 seek=$((thin_meta_sz)) 2> /dev/null
dd if=/dev/null of=/run/initramfs/thin-overlay/data bs=1b count=1 seek=$((thin_data_sz)) 2> /dev/null

THIN_META_LOOPDEV=$( losetup --show -f /run/initramfs/thin-overlay/meta )
THIN_DATA_LOOPDEV=$( losetup --show -f /run/initramfs/thin-overlay/data )

echo 0 $thin_data_sz thin-pool $THIN_META_LOOPDEV $THIN_DATA_LOOPDEV 1024 1024 | dmsetup create live-overlay-pool
dmsetup message /dev/mapper/live-overlay-pool 0 "create_thin 0"

# Create a snapshot of the base image
echo 0 $sz thin /dev/mapper/live-overlay-pool 0 $base | dmsetup create live-rw
else
echo 0 $sz snapshot $base $over p 8 | dmsetup create live-rw
fi

# Create a device that always points to a ro base image
echo 0 $sz linear $base 0 | dmsetup create --readonly live-base