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

From: Ric Wheeler
Date: Fri Dec 07 2012 - 16:47:00 EST

On 12/07/2012 04:14 PM, Theodore Ts'o wrote:
On Fri, Dec 07, 2012 at 02:30:19PM -0500, Steven Rostedt wrote:
How is this similar? By adding this bit, we removed incentive from a
group of developers that have the means to fix the real issue at hand
(the performance problem with ext4). Thus, it means that they have a work
around that's good enough for them, but the rest of us suffer.
That assumes that there **is** a way to claw back the performance
loss, and Chris Mason has demonstrated the performance hit exists with
xfs as well (950 MB/s vs. 400 MB/s; that's more than a factor of two).
Sometimes, you have to make the engineering tradeoffs. That's why
we're engineers, for goodness sakes. Sometimes, it's just not
possible to square the circle.

I don't believe that the technique of forcing people who need that
performance to suffer in order to induce them to try to engineer a
solution which may or may not exist is really the best or fairest way
to go about things.

- Ted

This is not a generally useful feature and won't ship in a way that helps most users with this issue.

Let's fix the problem properly.

In the meantime, there are several obvious ways to avoid this performance hit without changing the kernel (fully allocate and write the data, certainly reasonable for even reasonable sized files).


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