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>

diff --git a/dracut.cmdline.7.asc b/dracut.cmdline.7.asc
index 60826a1f1d0fc18387dc5ca7c2745663d1875bff..9ddad0f36d9eec3c537de9ad3236128feb25c0d9 100644 (file)
--- a/dracut.cmdline.7.asc
+++ b/dracut.cmdline.7.asc
@@ -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)__.

diff --git a/modules.d/90dmsquash-live/dmsquash-live-root.sh b/modules.d/90dmsquash-live/dmsquash-live-root.sh
index 9c08e9454f0ec1d3022b799c934a9b34c05ac09d..45f724cbdc089d3c3ed6fcd735a096d0a0b42e53 100755 (executable)
--- a/modules.d/90dmsquash-live/dmsquash-live-root.sh
+++ b/modules.d/90dmsquash-live/dmsquash-live-root.sh
@@ -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