zfs arc and amount of wired memory

Andriy Gapon avg at FreeBSD.org
Wed Feb 8 20:29:48 UTC 2012

on 08/02/2012 12:31 Eugene M. Zheganin said the following:
> Hi.
> On 08.02.2012 02:17, Andriy Gapon wrote:
>> [output snipped]
>> Thank you.  I don't see anything suspicious/unusual there.
>> Just case, do you have ZFS dedup enabled by a chance?
>> I think that examination of vmstat -m and vmstat -z outputs may provide some
>> clues as to what got all that memory wired.
> Nope, I don't have deduplication feature enabled.

OK.  So, did you have a chance to inspect vmstat -m and vmstat -z?

> By the way, today, after eating another 100M of wired memory this server hanged
> out with multiple non-stopping messages
> swap_pager: indefinite wait buffer
> Since it's swapping on zvol, it looks to me like it could be the mentioned in
> another thread here ("Swap on zvol - recommendable?") resource starvation issue;
> may be it happens faster when the ARC isn't limited.

It could be very well possible that swap on zvol doesn't work well when the
kernel itself is starved on memory.

> So I want to ask - how to report it and what should I include in such pr ?

I am leaving swap-on-zvol issue aside.  Your original problem doesn't seem to be
ZFS-related.  I suspect that you might be running into some kernel memory leak.
 If you manage to reproduce the high wired value again, then vmstat -m and
vmstat -z may provide some useful information.

In this vein, do you use any out-of-tree kernel modules?
Also, can you try to monitor your system to see when wired count grows?

Andriy Gapon

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