linux-ext4 - Re: [PATCH 4/7][TAKE5] support new modes in fallocate

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Message-ID: <20070626104546.GB19870@amitarora.in.ibm.com>
Date:	Tue, 26 Jun 2007 16:15:46 +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 Mon, Jun 25, 2007 at 03:52:39PM -0600, Andreas Dilger wrote:
> On Jun 25, 2007  19:15 +0530, Amit K. Arora wrote:
> > +#define FA_FL_DEALLOC	0x01 /* default is allocate */
> > +#define FA_FL_KEEP_SIZE	0x02 /* default is extend/shrink size */
> > +#define FA_FL_DEL_DATA	0x04 /* default is keep written data on DEALLOC */
> 
> 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() :  

@@ -2122,6 +2160,8 @@ int ext4_ext_get_blocks(handle_t *handle
        /* try to insert new extent into found leaf and return */
        ext4_ext_store_pblock(&newex, newblock);
        newex.ee_len = cpu_to_le16(allocated);
+       if (create == EXT4_CREATE_UNINITIALIZED_EXT)  /* Mark uninitialized */
+               ext4_ext_mark_uninitialized(&newex);
        err = ext4_ext_insert_extent(handle, inode, path, &newex);
        if (err) {
                /* free data blocks we just allocated */


> In that light, please change the comment to /* default is keep existing data */
> so that it doesn't imply this is only for DEALLOC.

Ok. Will update the comment.

Thanks!
--
Regards,
Amit Arora
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