Re: Strange ARC/Swap/CPU on yesterday's -CURRENT

From: Tom Rushworth <>
Date: Sun, 11 Mar 2018 16:19:05 -0700
Hi All,

On 11/03/2018 13:43, Jeff Roberson wrote:
> Hi Folks,
> This could be my fault from recent NUMA and concurrency related work.  I
> did touch some of the arc back-pressure mechanisms.  First, I would like
> to identify whether the wired memory is in the buffer cache.  Can those
> of you that have a repro look at sysctl vfs.bufspace and tell me if that
> accounts for the bulk of your wired memory usage?  I'm wondering if a
> job ran that pulled in all of the bufs from your root disk and filled up
> the buffer cache which doesn't have a back-pressure mechanism.  Then arc
> didn't respond appropriately to lower its usage.
> Also, if you could try going back to r328953 or r326346 and let me know
> if the problem exists in either.  That would be very helpful.  If anyone
> is willing to debug this with me contact me directly and I will send
> some test patches or debugging info after you have done the above steps.
> Thank you for the reports.
> Jeff

I'm seeing this on 11.1 stable r330126 with 32G of memory.  I have two
physical storage devices (one SSD, one HD) each a separate ZFS pool and
I can reproduce this fairly easily and quickly with:

   cp -r <dir_on_one_pool_with_lots_of_small_files> <dir_on_other_pool>

The directory being copied has about 25G (from du -sg), I end up with
16G wired after starting with less than 1G.  After the copy:
   sysctl vfs.bufspace  --> 0

Out of curiosity I copied it back the other way and drove the wired
memory to 26G during the copy falling back to 24G once the copy
finished, with vfs.bufspace at 0.

I'm not really in a good position to roll back to r328953 (or anything
much earlier), my graphics HW (i915) needs something pretty recent.

I am running a custom kernel (I dropped a lot of the newtwork
interfaces), so if you need more info I'm willing to help, as long as
you explain what you need in short words :).  (I'm not very familiar
with FreeBSD kernel work or sysadmin.)


Tom Rushworth
Received on Sun Mar 11 2018 - 22:19:11 UTC

This archive was generated by hypermail 2.4.0 : Wed May 19 2021 - 11:41:15 UTC