Hello,

A quick question on dm-integrity. Does dm-integrity layer honors fsync?

I was testing dm-integrity and performance. It had a strange result that
using dm-integrity with journal is faster than a normal file system or
dm-integrity with bitmap (no journal). fio is used for testing the storage
performance. The device is a SATA hard disk drive. Then I created a 100GB
partition for testing.

Below is the test cases:

1) XFS on a partition directly test case

2) dm-integrity: crc32c on a partition with default setting journal commit
interval is 10 seconds. Then create XFS on it. test case

3) dm-integrity: crc32c on a partition default setting journal commit
interval set to 5 seconds. Then create XFS on it.

4) dm-integrity:  crc32c on a partition default setting but using bitmap
instead of journal. Then create XFS on it.

FIO command:

fio --filename=./t1 --direct=1 --rw=randrw --refill_buffers --norandommap
--randrepeat=0 --ioengine=sync --bs=4k --rwmixread=75 --iodepth=16
--numjobs=8 --runtime=60 --group_reporting --fsync=1 --name=4ktest
--size=4G

Result:

   1. Read/Write IOPS: 117/41. Read/Write Speed 481KB/s 168KB/s
   2. Read/Write IOPS: 178/59. Read/Write Speed 732KB/s 244KB/s
   3. Read/Write IOPS: 169/57. Read/Write Speed 695KB/s 236KB/s
   4. Read/Write IOPS: 97/32. Read/Write Speed 400K/s 131KB/s

The original discussion in:
https://gitlab.com/cryptsetup/cryptsetup/issues/513 . Milan Broz said the
dm-devel mailing list is a suitable place to discuss the probem.

Thanks in advance.

Patrick