svn commit: r270759 - in head/sys: cddl/compat/opensolaris/kern cddl/compat/opensolaris/sys cddl/contrib/opensolaris/uts/common/fs/zfs vm

[Andriy Gapon]

on 02/09/2014 19:01 John Baldwin said the following:
> I know Steven has since committed a fix, but if there are still concerns, I 
> think it would be best to not just revert this entirely but to spend some time  
> fixing the remaining issues.  Clearly this issue affects a lot of users and 
> the earlier fixes to pagedaemon were not sufficient to fix their issues alone.

I am not sure that that is the case.  I could have very well missed an evidence
of that, but then I'd appreciate a pointer or two to such reports.
I am certainly sure that a large number of reports about "ZFS vs swapping" issue
appeared after the pagedaemon problem was introduced.

I have also missed any "theoretical" justification for the patch.  That is, an
explanation of how the patch interacts with the pagedaemon and improves things.
The empirical evidence could be insufficient, because it's easy to tilt the
balance such that the ARC gives in too easily.  But people who were affected by
the opposite problem could be different from people who would be affected by the
new problem, because of differences in system characteristics such as amount of
RAM, workload patterns, working set sizes, etc.

Having said that, I do not ask for the changes to be reverted, but I'll probably
get back after I have sufficient time to look at the patch and also to test its
effect on my systems.  This might not be very soon though.

P.S. I think that there was no technical reason to initialize the newly
introduced parameters via SYSINIT mechanism.  I think that the initialization
could be just done in arc_init.  And the newly added kmem_foo() functions
probably do not belong in cddl/compat/opensolaris as Solaris / illumos does not
have those functions.  I think that in this case e.g. vm_cnt.v_free_target can
just be used directly by the FreeBSD-specific ARC code.
-- 
Andriy Gapon