zfs very poor performance compared to ufs due to lack of cache?

[jhell]

On 09/05/2010 09:19, Steven Hartland wrote:
>> ----- Original Message ----- From: "jhell" <jhell at DataIX.net>
>>>
>>> Attached is the needfree patch mentioned in the URL alongside a local
>>> system patch to adjust kern.maxusers to no more than 512 on systems that
>>> can support it...
> 
> No joy, still drops down to arc_min even with those two patches and
> changing
> to vm_paging_needed from the post Artem mentioned:
> http://lists.freebsd.org/pipermail/freebsd-hackers/2010-August/032731.html
> 
> So I suspect if I hadn't put in a high arc_min as well it would be back
> down
> at silly low levels.
> 
> top shows:-
> 
> Mem: 26M Active, 1360M Inact, 2434M Wired, 6188K Cache, 418M Buf, 117M Free
> Swap: 4096M Total, 15M Used, 4081M Free
> 
> ARC Size:
>        Current Size:                   57.14%  2048.00M (arcsize)
>        Target Size: (Adaptive)         57.14%  2048.00M (c)
>        Min Size (Hard Limit):          57.14%  2048.00M (c_min)
>        Max Size (High Water):          ~1:1    3584.00M (c_max)
> 
> So there's still 1.3G of mem sitting inact, don't know what caused that but
> its essentially dead memory now it seems.
> 
> I know I could raise arc_min even further but that could be dangerous?
> 
> Any other suggestions? It seems like arc needs to cooperate with the
> rest of the OS pagedaemon more?

I am not exactly sure what your source is right now but guessing its at
least 8.1-RELEASE & hoping its 8.1-STABLE.

Line 3656 & 3657 of arc.c ? what are they ?

Do they look like the following,
3656:  uint64_t available_memory = ptoa((uintmax_t)cnt.v_free_count
3657:      + cnt.v_cache_count);


Regards,

-- 

 jhell,v