kern/187594: [zfs] [patch] ZFS ARC behavior problem and fix

[Adrian Gschwend]

On 18.03.14 18:45, Andriy Gapon wrote:

>> This is consistent with what I and others have observed on both 9.2
>> and 10.0; the ARC will expand until it hits the maximum configured
>> even at the expense of forcing pages onto the swap. In this
>> specific machine's case left to defaults it will grab nearly all
>> physical memory (over 20GB of 24) and wire it down.

> Well, this does not match my experience from before 10.x times.

I reported the issue on which Karl gave feedback and developed the
patch. The original thread of my report started here:

http://lists.freebsd.org/pipermail/freebsd-fs/2014-March/019043.html

Note that I don't have big memory eaters like VMs, it's just a bunch of
jails and services running in them. Including some JVMs.

Check out the munin graphs before and after:

Daily which does not seem to grow much anymore now:
http://ktk.netlabs.org/misc/munin-mem-zfs1.png

Weekly:
http://ktk.netlabs.org/misc/munin-mem-zfs2.png

You can actually see where I activated the patch (16.3), the system
behaves *much* better since then. I did one more reboot that's why it
goes down again but since then I did not reboot anymore.

The moments where munin did not report anything the system was in the
ARC-swap lock and virtually dead. From working on the system it feels
like a new machine, everything is super fast and snappy.

I don't understand much of the discussions you guys are having but I'm
pretty sure Karl fixed an issue which gave me headache on BSD over
years. I first saw this in 8.x when I started to use ZFS productively
and I've seen it in all 9.x release as well up to this patch.

regards

Adrian