dm: add new loop and ram targets

Enhancing IO performance compared to the kernels existing loop driver thus better suiting respective requirements in test setups, this patch series adds new "loop" and "ram" targets.

For measures see test results below.

The "loop" target maps segments to backing files.
Mapping table example:
0 4192256 loop /tmp/mapper_loop1
4192256 2097152 loop /dev/nvm/mapper_loop0

The "ram" target accesses RAM directly rather than through tmpfs additionally enhancing performance compared to "loop" thus avoding filesystem overhead.
Mapping table example:
0 8388608 ram

"ram" is a singleton target.

Performance test results for 4K and 32K IOPS comparing the loop driver with dm-loop backed by tmpfs and dm-ram (all 2GiB backing size):

<TESTSCRIPT>
#!/bin/sh
for f in /tmp/loop0 /tmp/mapper_loop0
do
dd if=/dev/zero of=$f bs=256M count=8 iflag=fullblock
done

losetup /dev/loop0 /tmp/loop0
sectors=du -s /tmp/mapper_loop0|cut -f1
dmsetup create loop0 --table "0 $sectors loop /tmp/mapper_loop0" dmsetup create ram --table "0 $sectors ram"

for bs in 4K 32K
do

	for d in /dev/loop0 /dev/mapper/loop0 /dev/mapper/ram
	do
		echo 3 > /proc/sys/vm/drop_caches
		fio --bs=$bs --rw=randrw --numjobs=99 --group_reporting --iodepth=12 --runtime=3 --ioengine=libaio \
		    --loops=1 --direct=1 --exitall --name dc --filename=$d | egrep "read|write"
	done

done
</TESTSCRIPT>

<4K_RESULTS>
loop driver:
read: IOPS=226k, BW=881MiB/s (924MB/s)(2645MiB/3003msec)
write: IOPS=225k, BW=880MiB/s (923MB/s)(2643MiB/3003msec)
dm-loop target:
read: IOPS=425k, BW=1661MiB/s (1742MB/s)(4990MiB/3004msec)
write: IOPS=425k, BW=1662MiB/s (1743MB/s)(4992MiB/3004msec)
dm-ram target:
read: IOPS=636k, BW=2484MiB/s (2605MB/s)(7464MiB/3005msec)
write: IOPS=636k, BW=2484MiB/s (2605MB/s)(7464MiB/3005msec)
</4K_RESULTS>

<32K_RESULTS>
loop driver:
read: IOPS=55.5k, BW=1733MiB/s (1817MB/s)(5215MiB/3009msec)
write: IOPS=55.2k, BW=1726MiB/s (1810MB/s)(5195MiB/3009msec)
dm-loop target:
read: IOPS=110k, BW=3452MiB/s (3620MB/s)(10.1GiB/3006msec)
write: IOPS=110k, BW=3448MiB/s (3615MB/s)(10.1GiB/3006msec)
dm-ram target:
read: IOPS=355k, BW=10.8GiB/s (11.6GB/s)(32.6GiB/3008msec)
write: IOPS=355k, BW=10.8GiB/s (11.6GB/s)(32.6GiB/3008msec)
</32K_RESULTS>

Heinz Mauelshagen (2):
dm loop: new target redirecting io to backing file(s) dm ram: new target redirecting io to RAM

 Documentation/device-mapper/loop.txt |  20 ++
 Documentation/device-mapper/ram.txt  |  15 ++
 drivers/md/Kconfig                   |  14 ++
 drivers/md/Makefile                  |   2 +
 drivers/md/dm-loop.c                 | 352 +++++++++++++++++++++++++++++++++++
 drivers/md/dm-ram.c                  | 101 ++++++++++
 6 files changed, 504 insertions(+)
 create mode 100644 Documentation/device-mapper/loop.txt
 create mode 100644 Documentation/device-mapper/ram.txt
 create mode 100644 drivers/md/dm-loop.c
 create mode 100644 drivers/md/dm-ram.c

2.14.3