Date: Sun, 07 Sep 2014 17:59:05 -0400 From: Nikolai Lifanov <lifanov@mail.lifanov.com> To: Steven Hartland <killing@multiplay.co.uk> Cc: src-committers@freebsd.org, Peter Wemm <peter@wemm.org>, John Baldwin <jhb@freebsd.org>, Alan Cox <alc@rice.edu>, svn-src-all@freebsd.org, Dmitry Morozovsky <marck@rinet.ru>, Andriy Gapon <avg@freebsd.org>, "Matthew D. Fuller" <fullermd@over-yonder.net>, svn-src-head@freebsd.org, owner-svn-src-head@freebsd.org Subject: Re: svn commit: r270759 - in head/sys: cddl/compat/opensolaris/kern cddl/compat/opensolaris/sys cddl/contrib/opensolaris/uts/common/fs/zfs vm Message-ID: <68e46bf0acca7eb6417cb847267f7bff@mail.lifanov.com> In-Reply-To: <86292055B4114529874B693EEB441CB6@multiplay.co.uk> References: <201408281950.s7SJo90I047213@svn.freebsd.org> <169C94ED141B435BACEADB04A4824717@multiplay.co.uk> <54072E20.10802@mail.lifanov.com> <2230377.GgKARkJyaG@ralph.baldwin.cx> <540778A2.3080809@mail.lifanov.com> <5407816B.9000401@FreeBSD.org> <86292055B4114529874B693EEB441CB6@multiplay.co.uk>
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On 2014-09-03 21:18, Steven Hartland wrote:
> ----- Original Message ----- From: "Andriy Gapon" <avg@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
I had time to re-test both the "stock" condition after the improvements
and the condition in which
vfs.zfs.arc_free_target=vm.stats.vm.v_free_min. It seems that MFU is
more likely to be reduced in the second case.
- Nikolai Lifanov
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