[dm-devel] [PATCH 0/2] dm-zoned: improve cache performance

[Damien Le Moal]

On 2020/05/13 16:07, Hannes Reinecke wrote:
> Hi all,
> 
> here are two patches to improve performance when a regular device
> is specified for dm-zoned.
> Damien noted that we have a performance drop after the zones on the
> regular device are used up, as then the random zones on the zoned
> device are being used, _and_ reclaim is running on the same disk.
> This slows down I/O whle using random zones, increasing again after
> the random zones are used up.
> This patchset fixes this by not allowing random zones for caching
> if a regular device is present.
> 
> Patch is relative to the dm-5.8 branch from
> git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git
> 
> As usual, comments and reviews are welcome.

Ran this for 2 hours, result plot attached. Same workload as before, 2 hours
run. This looks much better. No drop to near nothing as there is now no
HDD-to-HDD reclaim. The HDD is exercised at drive speed (150MB/s, which is about
what I get with ext4 on a similar regular drive without dm-zoned).

If anything, it looks like reclaim is starting too early. The initial peak
performance at SSD speed is now very very short. We need to check the
dmz_should_reclaim() changes.

> 
> 
> Hannes Reinecke (2):
>   dm-zoned: invert zone check in dmz_reset_zone()
>   dm-zoned: split off random and cache zones
> 
>  .../admin-guide/device-mapper/dm-zoned.rst    |  17 +-
>  drivers/md/dm-zoned-metadata.c                | 157 +++++++++++++-----
>  drivers/md/dm-zoned-reclaim.c                 |  70 ++++----
>  drivers/md/dm-zoned-target.c                  |  19 ++-
>  drivers/md/dm-zoned.h                         |   7 +-
>  5 files changed, 189 insertions(+), 81 deletions(-)
> 


-- 
Damien Le Moal
Western Digital Research
-------------- next part --------------
A non-text attachment was scrubbed...
Name: dm-zoned-cache.png
Type: image/png
Size: 205665 bytes
Desc: dm-zoned-cache.png
URL: <http://listman.redhat.com/archives/dm-devel/attachments/20200513/48b933c0/attachment.png>