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

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Message-ID: <50C263D6.9050003@redhat.com>
Date:	Fri, 07 Dec 2012 16:47:02 -0500
From:	Ric Wheeler <rwheeler@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Martin Steigerwald <Martin@...htvoll.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH, 3.7-rc7, RESEND] fs: revert commit bbdd6808 to fallocate
 UAPI

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).

Ric

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