Use swapfile if no extra device is present

We are booting instances outside of rax and they don't always come with
extra devices that can be repurposed for swap. If in that case then
create a swapfile instead.

Note we do not use fallocate as swapon's manpage says this is suboptimal
with the linux kernel's swap implementation.

Change-Id: I8b9ce18c18e4069aba7de27bb6a9927627b15b49

make_swap.sh

@@ -21,13 +21,14 @@ if [ `grep SwapTotal /proc/meminfo | awk '{ print $2; }'` -eq 0 ]; then
     elif [ -b /dev/xvde ]; then
         DEV='/dev/xvde'
     fi
+    SWAPFILE=/swapfile
+    MEMKB=`grep MemTotal /proc/meminfo | awk '{print $2; }'`
+    # Use the nearest power of two in MB as the swap size.
+    # This ensures that the partitions below are aligned properly.
+    MEM=`python3 -c "import math ; print(2**int(round(math.log($MEMKB/1024, 2))))"`
 
     # Avoid using config drive device for swap
     if [ -n "$DEV" ] && ! blkid | grep $DEV | grep TYPE ; then
-        MEMKB=`grep MemTotal /proc/meminfo | awk '{print $2; }'`
-        # Use the nearest power of two in MB as the swap size.
-        # This ensures that the partitions below are aligned properly.
-        MEM=`python3 -c "import math ; print(2**int(round(math.log($MEMKB/1024, 2))))"`
         if mount | grep ${DEV} > /dev/null; then
             echo "*** ${DEV} appears to already be mounted"
             echo "*** ${DEV} unmounting and reformating"
@@ -61,6 +62,16 @@ if [ `grep SwapTotal /proc/meminfo | awk '{ print $2; }'` -eq 0 ]; then
         perl -nle "m,${DEV}, || print" -i /etc/fstab
         echo "${DEV}1  none  swap  sw                           0  0" >> /etc/fstab
         echo "${DEV}2  /opt  ext4  errors=remount-ro,barrier=0  0  2" >> /etc/fstab
-        mount -a
+    elif [ ! -f "$SWAPFILE" ] ; then
+        # We don't have real devices to use so we make a swap file instead.
+        # Note you can skip this by precreating /swapfile.
+        # bs here is 1Mb
+        sudo dd if=/dev/zero of=${SWAPFILE} bs=1048576 count=${MEM}
+        sudo chown root:root $SWAPFILE
+        sudo chmod 600 $SWAPFILE
+        sudo mkswap $SWAPFILE
+        echo "${SWAPFILE}  none  swap  sw                       0  0" >> /etc/fstab
     fi
+    swapon -a
+    mount -a
 fi