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

[Andre Oppermann]

On 15.09.2010 17:38, Andriy Gapon wrote:
> on 15/09/2010 18:15 Andriy Gapon said the following:
>> on 15/09/2010 18:04 Steven Hartland said the following:
>>> Hmm, so taking a different track on the issue is the a way to make sendfile use data
>>> directly from ARC instead of having to copy it first?
>>
>> Well, theoretically everything is possible, but I am not sure if it's feasible.
>> It's a lot of work anyways, it should be a very specialized sendfile and a lot if
>> inter-layer knowledge and dependencies.
>> Don't hold your breath for it.
>
> Perhaps some middle-ground solution can be developed with less effort.
> This solution would be specific to filesystems that don't use buffer cache, so it
> wouldn't touch any pages, but instead it would use regular VOP_READ into a mbuf.
> So, there would be copying, but page caches won't be unnecessarily "polluted" with
> second copy of the data and this all would happen in kernel giving an advantage
> over userland solution with read(2)+send(2).

Is there a quick way of deciding within sendfile(2) whether a file resides
on a filesystem that doesn't use the buffer cache?

> Having said that, I see that OpenSolaris has a mechanism for something like that.
> The mechanism can either globally enabled or enabled for file over certain size.
> The mechanism uses dedicated kernel threads that get data using direct I/O, buffer
> and send it.
> That's my impression from a quick look, I may have gotten things wrong.

-- 
Andre