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

To: linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, David Chinner <dgc@xxxxxxx>, suparna@xxxxxxxxxx, cmm@xxxxxxxxxx, xfs@xxxxxxxxxxx
Subject: Re: [PATCH 4/7][TAKE5] support new modes in fallocate
From: "Amit K. Arora" <aarora@xxxxxxxxxxxxxxxxxx>
Date: Tue, 26 Jun 2007 16:15:46 +0530
In-reply-to: <20070625215239.GK5181@xxxxxxxxxxxxxxxxxxxx>
References: <20070511110301.GB28425@xxxxxxxxxx> <20070512080157.GF85884050@xxxxxxx> <20070612061652.GA6320@xxxxxxxxxxxxxxxxxxxx> <20070613235217.GS86004887@xxxxxxx> <20070614091458.GH5181@xxxxxxxxxxxxxxxxxxxx> <20070614120413.GD86004887@xxxxxxx> <20070614193347.GN5181@xxxxxxxxxxxxxxxxxxxx> <20070625132810.GA1951@xxxxxxxxxxxxxxxxxxxx> <20070625134500.GE1951@xxxxxxxxxxxxxxxxxxxx> <20070625215239.GK5181@xxxxxxxxxxxxxxxxxxxx>
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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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