Re: "zfs send" freezes system (was: Re: pgdaemon high CPU consumption)

[Brad Spencer <brad%anduin.eldar.org@localhost>]

Matthias Petermann <mp%petermann-it.de@localhost> writes:

[snip]

> Roundabout one week after removing the patch, my system with ZFS is 
> behaving "normally" for the most part and the freezes have disappeared. 
> What is the recommended way given the 10 branch? If it is not 
> foreseeable that the basic problem can be solved shortly, would it also 
> be an option to withdraw the patch in the sources to get at least a 
> stable behavior? (Not only) on the sidelines, I would still be 
> interested in whether this "zfs send" problem occurs in general, or 
> whether certain hardware requirements have a favorable effect on it.
>
> Kind regards
> Matthias


My personal experience with this problem is with Xen PV/PVH guests on my
build system(s), but I think others have experienced it with physical
systems.  The only particular facts that I have observed are: a) If
there is more memory given to the guest they last longer.  That is the
one with 8GB does not have as much trouble as the one with 4GB.  b)
reducing the number of vnodes makes helps keep the system up.  I usually
run 4096 to 16384 kern.maxvnodes.  Without this the OS build system can
do about 1.5 "build.sh release" runs before it hangs and with a
reduction in vnodes it can get away with 4 to 6 before there are
problems.  c) Seen only once and on -currentish (most systems are 9.2),
but a zfs receive into a compressed fileset hung after a while (in the
usual manor that I observe) even with the mentioned patch reverted and a
reduced maxvnodes.  Receiving into a non-compressed fileset worked as
expected.

The above a, b and c was 100% reproduceable for me, just takes a while as
a build release isn't quite.. the zfs receive thing happened much
faster.

Both of my build systems uses zfs send through a ssh pipe to a file on
another system as a backup method and both have compressed filesets, but
they are rarely received into and never sent from those.  I have had no
trouble zfs sending and receiving locally from a non-compressed fileset
into a compressed one, which makes that one case a little strange.

On a -currentish test system with zfs filesets for object artifacts and
build artifacts if I didn't revert the mentioned patch to arc.c the
system could not make it though a build of qemu from pkgsrc and maybe
not even though unpacking the source for building (sorry, don't exactly
remember how far it would get).




-- 
Brad Spencer - brad%anduin.eldar.org@localhost - KC8VKS - http://anduin.eldar.org