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

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Date:	Fri, 7 Dec 2012 16:43:25 -0500
From:	Chris Mason <chris.mason@...ionio.com>
To:	Theodore Ts'o <tytso@....edu>
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>,
	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 Fri, Dec 07, 2012 at 02:27:43PM -0700, Theodore Ts'o wrote:
> On Fri, Dec 07, 2012 at 04:09:32PM -0500, Chris Mason wrote:
> > Persistent trim is what I had in mind, but there are other ideas that do
> > imply a change in behavior as well.  Can we safely assume this feature
> > won't matter on spinning media?  New features like persistent
> > trim do make it much easier to solve securely, and using a bit for it
> > means we can toss back an error to the app if the underlying storage
> > isn't safe.
> 
> We originally implemented no hide stale for spinning media.  Some
> folks have claimed that for XFS their superior technology means that
> no hide stale doesn't buy them anything for HDD's.  I'm not entirely
> sure I buy this, since if you need to update metadata, it means at
> least one extra seek for each random write into 4k preallocated space,
> and 7200 RPM disks only have about 200 seeks per second.

True, 7200 RPM disks are slow, but even allowing them to expose stale
data just makes them a little less slow.

I know it's against the rules to pretend that disks don't matter.  But
really, once you're doing random IO into a spindle you've given up on
performance anyway.

-chris
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