Re: [PATCH, 3.7-rc7, RESEND] fs: revert commit bbdd6808 to fallocate UAPI

Chris Mason
2012-12-08T01:39:52Z

On Fri, Dec 07, 2012 at 05:17:05PM -0700, Dave Chinner wrote:
> On Fri, Dec 07, 2012 at 02:03:06PM -0500, Chris Mason wrote:

[ dead and beaten fallocate ponies ]

>
> > On a single flash drive doing random 4K writes, xfs does 950MB/s into
> > regular extents but only 400MB/s into preallocated extents.
> >
> > http://masoncoding.com/presentation/perf-linuxcon12/fallocate.png
>
> This is bordering on irrelevancy, but can you provide the workload
> you were running to generate this graph? Random 4k writes could be
> anything, really.

This one was fio aio/dio, I'll dig out the job file and rerun it on
3.7-rc on Monday. Any real random write is going to show this with
enough load.

>
> In my experience, applications that actually do processing between
> random write IOs don't see anywhere near the same degradation as
> such micro-benchmarks tend to indicate can occur with unwritten
> extents. Are you seeing this level of degradation in real-world applications?
> If you give me a reason to fix it (and the hardware to test it on),
> I'm pretty sure I can bring the overhead down to just a few percent
> on fully featured SSDs like FusionIO devices...

We should have a card I can send, drop me the address.

For the workload...that's harder. We can talk all day about what a
normal random write workload is, but if you have a fio job that you
think represents real world, I can run that.

[ much nodding ;) ]