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

Amit K. Arora
2007-06-26T10:45:41Z

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