Re: [PATCH v2] dm-integrity: Prevent RMW for full metadata buffer writes

From: Lukas Straub
Date: Thu Mar 26 2020 - 07:24:38 EST

On Tue, 24 Mar 2020 15:11:49 -0400
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:

> On Tue, Mar 24 2020 at 2:59pm -0400,
> Lukas Straub <lukasstraub2@xxxxxx> wrote:
>
> > On Tue, 24 Mar 2020 13:18:22 -0400
> > Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> >
> > > On Thu, Feb 27 2020 at 8:26am -0500,
> > > Lukas Straub <lukasstraub2@xxxxxx> wrote:
> > >
> > > > If a full metadata buffer is being written, don't read it first. This
> > > > prevents a read-modify-write cycle and increases performance on HDDs
> > > > considerably.
> > > >
> > > > To do this we now calculate the checksums for all sectors in the bio in one
> > > > go in integrity_metadata and then pass the result to dm_integrity_rw_tag,
> > > > which now checks if we overwrite the whole buffer.
> > > >
> > > > Benchmarking with a 5400RPM HDD with bitmap mode:
> > > > integritysetup format --no-wipe --batch-mode --interleave-sectors $((64*1024)) -t 4 -s 512 -I crc32c -B /dev/sdc
> > > > integritysetup open --buffer-sectors=1 -I crc32c -B /dev/sdc hdda_integ
> > > > dd if=/dev/zero of=/dev/mapper/hdda_integ bs=64K count=$((16*1024*4)) conv=fsync oflag=direct status=progress
> > > >
> > > > Without patch:
> > > > 4294967296 bytes (4.3 GB, 4.0 GiB) copied, 400.326 s, 10.7 MB/s
> > > >
> > > > With patch:
> > > > 4294967296 bytes (4.3 GB, 4.0 GiB) copied, 41.2057 s, 104 MB/s
> > > >
> > > > Signed-off-by: Lukas Straub <lukasstraub2@xxxxxx>
> > > > ---
> > > > Hello Everyone,
> > > > So here is v2, now checking if we overwrite a whole metadata buffer instead
> > > > of the (buggy) check if we overwrite a whole tag area before.
> > > > Performance stayed the same (with --buffer-sectors=1).
> > > >
> > > > The only quirk now is that it advertises a very big optimal io size in the
> > > > standard configuration (where buffer_sectors=128). Is this a Problem?
> > > >
> > > > v2:
> > > > -fix dm_integrity_rw_tag to check if we overwrite a whole metadat buffer
> > > > -fix optimal io size to check if we overwrite a whole metadata buffer
> > > >
> > > > Regards,
> > > > Lukas Straub
> > >
> > >
> > > Not sure why you didn't cc Mikulas but I just checked with him and he
> > > thinks:
> > >
> > > You're only seeing a boost because you're using 512-byte sector and
> > > 512-byte buffer. Patch helps that case but hurts in most other cases
> > > (due to small buffers).
> >
> > Hmm, buffer-sectors is still user configurable. If the user wants fast
> > write performance on slow HDDs he can set a small buffer-sector and
> > benefit from this patch. With the default buffer-sectors=128 it
> > shouldn't have any impact.
>
> OK, if you'd be willing to conduct tests to prove there is no impact
> with larger buffers that'd certainly help reinforce your position and
> make it easier for me to take your patch.
>
> But if you're just testing against slow HDD testbeds then the test
> coverage isn't wide enough.
>
> Thanks,
> Mike
>

Sure,
This time testing with an Samsung 850 EVO SSD:

without patch:

root@teststore:/home/lukas# integritysetup format --no-wipe --batch-mode -I crc32c -B /dev/sdc1
root@teststore:/home/lukas# integritysetup open -I crc32c -B /dev/sdc1 ssda_integ
root@teststore:/home/lukas# dd if=/dev/zero of=/dev/mapper/ssda_integ bs=64K count=$((16*1024*4)) conv=fsync oflag=direct status=progress
4177264640 bytes (4.2 GB, 3.9 GiB) copied, 28 s, 149 MB/s
65536+0 records in
65536+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 28.8946 s, 149 MB/s
root@teststore:/home/lukas# dd if=/dev/zero of=/dev/mapper/ssda_integ bs=4M count=$((256*4)) conv=fsync oflag=direct status=progress
4211081216 bytes (4.2 GB, 3.9 GiB) copied, 22 s, 191 MB/s
1024+0 records in
1024+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 22.6355 s, 190 MB/s
root@teststore:/home/lukas# time mkfs.ext4 /dev/mapper/ssda_integ 4g
mke2fs 1.45.5 (07-Jan-2020)
Creating filesystem with 1048576 4k blocks and 262144 inodes
Filesystem UUID: 679c4808-d549-4576-a8ef-4c46c78c6070
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736

Allocating group tables: done
Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done


real 0m0.318s
user 0m0.016s
sys 0m0.001s
root@teststore:/home/lukas# mount /dev/mapper/ssda_integ /mnt/
root@teststore:/home/lukas# cd /mnt/
root@teststore:/mnt# time tar -xJf /home/lukas/linux-5.5.4.tar.xz

real 0m18.708s
user 0m14.351s
sys 0m8.585s
root@teststore:/mnt# time rm -rf linux-5.5.4/

real 0m3.226s
user 0m0.117s
sys 0m2.958s


with patch:

root@teststore:/home/lukas# integritysetup format --no-wipe --batch-mode -I crc32c -B /dev/sdc1
root@teststore:/home/lukas# integritysetup open -I crc32c -B /dev/sdc1 ssda_integ
root@teststore:/home/lukas# dd if=/dev/zero of=/dev/mapper/ssda_integ bs=64K count=$((16*1024*4)) conv=fsync oflag=direct status=progress
4169007104 bytes (4.2 GB, 3.9 GiB) copied, 27 s, 154 MB/s
65536+0 records in
65536+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 27.9165 s, 154 MB/s
root@teststore:/home/lukas# dd if=/dev/zero of=/dev/mapper/ssda_integ bs=4M count=$((256*4)) conv=fsync oflag=direct status=progress
4169138176 bytes (4.2 GB, 3.9 GiB) copied, 22 s, 189 MB/s
1024+0 records in
1024+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 22.9181 s, 187 MB/s
root@teststore:/home/lukas# time mkfs.ext4 /dev/mapper/ssda_integ 4g
mke2fs 1.45.5 (07-Jan-2020)
Creating filesystem with 1048576 4k blocks and 262144 inodes
Filesystem UUID: 9a9decad-19e2-46a4-8cc5-ce27238829f2
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736

Allocating group tables: done
Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done


real 0m0.341s
user 0m0.000s
sys 0m0.016s
root@teststore:/home/lukas# mount /dev/mapper/ssda_integ /mnt/
root@teststore:/home/lukas# cd /mnt/
root@teststore:/mnt# time tar -xJf /home/lukas/linux-5.5.4.tar.xz

real 0m18.409s
user 0m14.191s
sys 0m8.585s
root@teststore:/mnt# time rm -rf linux-5.5.4/

real 0m3.200s
user 0m0.133s
sys 0m2.979s


Regards,
Lukas Straub

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