patch which implements ZFS LZ4 compression

[Oliver Brandmueller]

Hi,

On Sat, Feb 09, 2013 at 12:44:36PM -0800, Jeremy Chadwick wrote:
> Bottom line: people enable compression on an fs, issue large amounts of
> write I/O to that fs (say hundreds of megabytes, or gigabytes), and
> start to see the entire system intermittently stalling hard (for
> multiple seconds at a time).  This affects everything from switching VTs
> on physical console to packets going across SSH.  The stalls vary in
> duration depending on what compression type is used (lzjb vs. gzip-1 --
> I cannot even imagine what gzip-9 would be like).  I described it as
> verbosely as I could, including going back and "re-testing" because
> people felt the "ZFSv28 import might have addressed it" (it did not):
> 
> http://lists.freebsd.org/pipermail/freebsd-fs/2011-October/012752.html
> 
> The exact same behaviour happens if dedup is used.  There is no relation
> between compression (the feature) and dedup (the feature), obviously,
> but the symptom I've described matches Bob's explanation perfectly.
> 
> If you want to provide the aforementioned instructions, I'll happily
> follow them.

Did you try using 4BSD instead of ULE at some point? I had similar 
problems and that completely fixed it for me. Which would mean, that 
there's some interactio between scheduler and ZFS code.

- Oliver

-- 
| Oliver Brandmueller          http://sysadm.in/         ob at sysadm.in |
|                        Ich bin das Internet. Sowahr ich Gott helfe. |