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Btrfs: adjust len of writes if following a preallocated extent 

If we have

|0--hole--4095||4096--preallocate--12287|

instead of using preallocated space, a 8K direct write will just
create a new 8K extent and it'll end up with

|0--new extent--8191||8192--preallocate--12287|

It's because we find a hole em and then go to create a new 8K
extent directly without adjusting @len.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: Chris Mason <clm@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Liu Bo 2016-11-04 12:20:54 -07:00 committed by David Sterba
parent 7b9ea6279b
commit a23eaa875f
1 changed files with 5 additions and 3 deletions
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8
fs/btrfs/inode.c
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@ -7782,10 +7782,12 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
}
/*
* this will cow the extent, reset the len in case we changed
* it above
* this will cow the extent, if em is within [start, len], then
* probably we've found a preallocated/existing extent, let's
* give it a chance to use preallocated space.
*/
len = bh_result->b_size;
len = min_t(u64, bh_result->b_size, em->len - (start - em->start));
len = ALIGN(len, root->sectorsize);
free_extent_map(em);
em = btrfs_new_extent_direct(inode, start, len);
if (IS_ERR(em)) {