Re: [Nbd] NBD kernel module, client and server with support for TRIM

[katon goukakyuuno <katongoukakyuuno@...223...>]

A few observations --

1) When I remove the line "trim = true" from the config file and also
remove all mount options while mounting (the effective command being
"mount -t ext4 /dev/nbd0 /mnt/remote"), I find that the size of the
NBD backend file remains the same after the large file is deleted from
the filesystem.

2) If I include the 'data=journal' option while mounting (mount -t
ext4 -odata=journal /dev/nbd0 /mnt/remote), I find that the NBD
backend file shrinks. What is happening here exactly? I haven't
include the words 'trim' or 'discard' anywhere and still the results
indicate that TRIM is working by enabling the mount option
'data=journal'?

Thanks,
T G

On Mon, Mar 19, 2012 at 11:43 AM, katon goukakyuuno
<katongoukakyuuno@...223...> wrote:
> Hi Wouter,
>
> I wrote the following bash script - discard.sh - which tests the TRIM
> command on a kernel that has been patched to support it. This script
> is based on the "maketr" script that already exists in the nbd-3.0
> directory available for download.
>
> #!/bin/sh
> #
> # Example script to test the TRIM command
> # Must be run as root. Remember to chown the file afterwards
>
> tmpnam=`mktemp`
> conffile=${tmpnam}.conf
> pidfile=${tmpnam}.pid
>
> ulimit -c unlimited
>
> echo "\n$0: Clearing dmesg...\n"
> dmesg -c > /dev/null
>
> cat >${conffile} <<EOF
> [generic]
> [export1]
>        exportname = $tmpnam
>        trim = true
> EOF
> ./nbd-server -C ${conffile} -p ${pidfile} &
> PID=$!
>
> dd if=/dev/zero of=${tmpnam} bs=1M count=256
> ./nbd-client -N export1 127.0.0.1 /dev/nbd0
> mkfs.ext4 /dev/nbd0
>
> echo "$0: mounting ext4 with \"discard\" option\n"
> mount -t ext4 -odata=journal,discard /dev/nbd0 /mnt/remote
> (cd /mnt/remote ; dd if=/dev/zero of=/mnt/remote/trial.img count=50
> bs=512; sync) 2>&1 >/dev/null
> echo "\n$0: \"du\" output after creating temp file\n"
> du ${tmpnam}
> echo
> rm -f /mnt/remote/trial.img ; sync
> echo "\n$0: \"du\" output after deleting temp file\n"
> du ${tmpnam}
>
> umount /mnt/remote
> ./nbd-client -d /dev/nbd0
> if [ -f ${pidfile} ]
> then
>        kill `cat ${pidfile}`
>        rm -f ${pidfile}
> else
>        kill $PID
> fi
> rm -f $tmpnam ${conffile}
> echo "\n$0: Dumping dmesg:\n"
> dmesg
>
> On running, I get the following output (I'm showing only the more
> important messages):
>
> ./discard.sh: Clearing dmesg...
>
> ./discard.sh: mounting ext4 with "discard" option
>
> # Output of: dd if=/dev/zero of=/mnt/remote/trial.img count=50 bs=512
> 50+0 records in
> 50+0 records out
> 25600 bytes (26 kB) copied, 0.000411365 s, 62.2 MB/s
>
> ./discard.sh: "du" output after creating temp file
>
> 262200  /tmp/tmp.OdfAMDXMCL
>
> ./discard.sh: "du" output after deleting temp file
>
> 262168  /tmp/tmp.OdfAMDXMCL
> Disconnecting: que, disconnect, sock, done
>
> ./discard.sh: Dumping dmesg:
>
> [ 5321.494980] EXT4-fs (nbd0): mounted filesystem with journalled data
> mode. Opts: data=journal,discard
> [ 5325.478361] block nbd0: NBD_DISCONNECT
> [ 5325.478813] block nbd0: Receive control failed (result -32)
> [ 5325.478854] block nbd0: queue cleared
>
> It looks like TRIM is working perfectly on my patched kernel! :-)
>
> BTW, looking at dmesg, there is a broken pipe error. Is that something
> to worry about?
>
> Thanks,
> T G
>
> On Fri, Mar 16, 2012 at 10:58 AM, Wouter Verhelst <w@...112...> wrote:
>>
>> On Fri, Mar 16, 2012 at 10:42:03AM -0700, katon goukakyuuno wrote:
>> > Hi Wouter,
>> >
>> > Thank you very much for replying! I have patched my kernel to support
>> > only
>> > TRIM. I hope I need not apply the patch for FLUSH/FUA as well to just
>> > use TRIM?
>> > I hope all patches are added to the latest Linux kernel soon!
>> >
>> > I have also updated the nbd client and server to version 3.0 (the latest
>> > version) which does support TRIM.
>> >
>> > How do I test if TRIM is working properly on my system? Are there any
>> > test
>> > scripts readily available;
>>
>> Not at this time. In fact, while I expect it to be working, I haven't
>> actually tested it much myself.
>>
>> > or, do I need to create a new /dev/nbd and mount a
>> > file system which supports TRIM and then try to issue some commands from
>> > userspace? I haven't completely figured out this part yet.
>>
>> Something like that. This should work:
>> - set the 'trim' option to 'true' in an nbd export
>> - connect to that NBD export from a client (may be the same machine)
>> - create an ext4 filesystem on that device
>> - mount the filesystem with the option 'discard'
>> - create a large file on the filesystem
>> - sync
>> - run 'du' on the nbd backend file
>> - remove the file
>> - sync again
>> - run 'du' again, and see if the file is now smaller. If it is, then a
>>  TRIM command was sent successfully to the server.
>>
>> --
>> The volume of a pizza of thickness a and radius z can be described by
>> the following formula:
>>
>> pi zz a