linux-ext4 - Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super

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Message-ID: <20101118143101.GO5618@dhcp231-156.rdu.redhat.com>
Date:	Thu, 18 Nov 2010 09:31:01 -0500
From:	Josef Bacik <josef@...hat.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Josef Bacik <josef@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>, tytso@....edu,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org,
	sandeen@...hat.com
Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate
	super_operation

On Thu, Nov 18, 2010 at 07:19:58AM -0700, Matthew Wilcox wrote:
> On Thu, Nov 18, 2010 at 08:48:04AM -0500, Josef Bacik wrote:
> > On Thu, Nov 18, 2010 at 06:06:30AM -0700, Matthew Wilcox wrote:
> > > On Thu, Nov 18, 2010 at 08:36:48AM +0100, Lukas Czerner wrote:
> > > > There was concern that FITRIM ioctl is not common enough to be included
> > > > in core vfs ioctl, as Christoph Hellwig pointed out there's no real point
> > > > in dispatching this out to a separate vector instead of just through
> > > > ->ioctl.
> > > 
> > > Um, are you and Josef working independently of each other?  You don't
> > > seem to be cc'ing each other on your patches, and you're basically doing
> > > the same thing.
> > >
> > 
> > I guess they are the same thing in that we're both dealing with free'ing up
> > space, but thats about where the similarities end.  Lukas' work is in TRIM'ing
> > already free'd space, mine is in creating free'd space.  Plus I don't know
> > anything nor wish to ever know anything about TRIM ;).  Thanks,
> 
> I guess I was assuming that, on receiving a FALLOC_FL_PUNCH_HOLE, a
> filesystem that was TRIM-aware would pass that information down to the
> block device that it's mounted on.  I strongly feel that we shouldn't
> have two interfaces to do essentially the same thing.

But they aren't doing the same thing, his is discarding already free'd space,
I'm enabling people to de-allocate space in the middle of files, they are two
seperate things.  Of course if the filesystem is TRIM aware the de-allocation
would lead to a TRIM, but not if the filesystem isn't mounted with -o discard.
Hole punching is useful independantly of the ability to do TRIM.  Thanks,

Josef
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