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

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Date:	Fri, 7 Dec 2012 20:39:49 -0500
From:	Chris Mason <chris.mason@...ionio.com>
To:	Dave Chinner <david@...morbit.com>
CC:	Chris Mason <clmason@...ionio.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ric Wheeler <rwheeler@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Martin Steigerwald <Martin@...htvoll.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH, 3.7-rc7, RESEND] fs: revert commit bbdd6808 to fallocate
 UAPI

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 ;) ]
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