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

[Steven Hartland]

----- Original Message ----- 
From: "Andriy Gapon" <avg at FreeBSD.org>


> on 03/09/2014 23:22 Nikolai Lifanov said the following:
>> On 09/03/14 15:22, John Baldwin wrote:
>>> On Wednesday, September 03, 2014 11:05:04 AM Nikolai Lifanov wrote:
>>>> On 09/03/14 04:09, Steven Hartland wrote:
>>>>> I'm looking to MFC this change so wanted to check if
>>>>> anyone had an final feedback / objections?
>>>>>
>>>>> I know we currently have Alan's feedback on changing
>>>>> the #ifdef __i386__ to #ifndef UMA_MD_SMALL_ALLOC
>>>>> which sounds sensible but waiting Peter to comment on.
>>>>>
>>>>>    Regards
>>>>>    Steve
>>>>
>>>> I have no technical input, but this change improves ARC usefulness for
>>>> me quite a bit. I would like to see the improvement in 10-STABLE.
>>>
>>> Can you verify that the current 10-STABLE (as of today) with all the various 
>>> pagedaemon fixes still has ARC issues for your workload?
>>>
>> 
>> It doesn't have any issues, but I noticed the improvement on CURRENT. I
>> observed that just after this change, my package builder is much more
>> likely to retain MFU and not evict useful things from there (the port
>> tree) after large builds.
>> However, I run a lot more 10.0-RELEASE than CURRENT and I would like to
>> see this improvement release-bound.
>> 
>> I would be happy to test this on 10-STABLE if you think that this is
>> relevant.
> 
> 
> As noted before, unfortunately, this commit (plus its fixups) contains at least
> two related but distinct changes.  So, to separate the wheat from the chaff,
> could you please try to comment out the following block in
> sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c, function arc_reclaim_needed:
> 
>        if (kmem_free_count() < zfs_arc_free_target) {
>                DTRACE_PROBE2(arc__reclaim_freetarget, uint64_t,
>                    kmem_free_count(), uint64_t, zfs_arc_free_target);
>                return (1);
>        }
> 
> Alternatively, I think that the same effect can be achieved by setting sysctl
> vfs.zfs.arc_free_target to the same value as vm.stats.vm.v_free_min.

Thats correct that would achieve the same thing.

> It's interesting to me whether you would still see the better performance or if
> that improvement would be undone.

Indeed that would be interesting, but we might find that its quite memory size
dependent given the scaling so confirming HW details would be nice too.

I'd also be interested to know who wins the free race between the VM and ARC
when using that value.

For those following this thread but not the review, I've added some additional
information there which you might be interested in:
https://reviews.freebsd.org/D702

    Regards
    Steve