linux-kernel - Re: [PATCH 4/7][TAKE5] support new modes in fallocate

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Message-ID: <20070626191215.GB13324@amitarora.in.ibm.com>
Date:	Wed, 27 Jun 2007 00:42:15 +0530
From:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
To:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, David Chinner <dgc@....com>,
	suparna@...ibm.com, cmm@...ibm.com, xfs@....sgi.com
Subject: Re: [PATCH 4/7][TAKE5] support new modes in fallocate

On Tue, Jun 26, 2007 at 11:42:50AM -0400, Andreas Dilger wrote:
> On Jun 26, 2007  16:15 +0530, Amit K. Arora wrote:
> > On Mon, Jun 25, 2007 at 03:52:39PM -0600, Andreas Dilger wrote:
> > > In XFS one of the (many) ALLOC modes is to zero existing data on allocate.
> > > For ext4 all this would mean is calling ext4_ext_mark_uninitialized() on
> > > each extent.  For some workloads this would be much faster than truncate
> > > and reallocate of all the blocks in a file.
> > 
> > In ext4, we already mark each extent having preallocated blocks as
> > uninitialized. This is done as part of following code (which is part of
> > patch 5/7) in ext4_ext_get_blocks() :  
> 
> What I meant is that with XFS_IOC_ALLOCSP the previously-written data
> is ZEROED OUT, unlike with fallocate() which leaves previously-written
> data alone and only allocates in holes.
> 
> In order to specify this for allocation, FA_FL_DEL_DATA would need to make
> sense for allocations (as well as the deallocation).  This is farily easy
> to do - just mark all of the existing extents as unallocated, and their
> data disappears.

Ok, agreed. Will add the FA_ZERO_SPACE mode too.
Thanks!

--
Regards,
Amit Arora
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