Btrfs: send, fix file hole not being preserved due to inline extent
PATCH 1/1 Btrfs: send, fix file hole not being preserved due to inline extent
From: Filipe Manana <[email protected]>
Normally we don't have inline extents followed by regular extents, but there's currently at least one harmless case where this happens. For example, when the page size is 4Kb and compression is enabled:
$ mkfs.btrfs -f /dev/sdb $ mount -o compress /dev/sdb /mnt $ xfs_io -f -c "pwrite -S 0xaa 0 4K" -c "fsync" /mnt/foobar $ xfs_io -c "pwrite -S 0xbb 8K 4K" -c "fsync" /mnt/foobar
In this case we get a compressed inline extent, representing 4Kb of data, followed by a hole extent and then a regular data extent. The inline extent was not expanded/converted to a regular extent exactly because it represents 4Kb of data. This does not cause any apparent problem (such as the issue solved by commit e1699d2d7bf6 ("btrfs: add missing memset while reading compressed inline extents")) except trigger an unexpected case in the incremental send code path that makes us issue an operation to write a hole when it's not needed, resulting in more writes at the receiver and wasting space at the receiver.
So teach the incremental send code to deal with this particular case.
The issue can be currently triggered by running fstests btrfs/137 with compression enabled (MOUNT_OPTIONS="-o compress" ./check btrfs/137).
--- fs/btrfs/send.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)
fs/btrfs/send.c +21 -2
@@ -5184,13 +5184,19 @@ static int is_extent_unchanged(struct send_ctx *sctx,while (key.offset < ekey->offset + left_len) { ei = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item); right_type =btrfs_file_extent_type (eb, ei); -if (right_type !=BTRFS_FILE_EXTENT_REG ) { +if (right_type !=BTRFS_FILE_EXTENT_REG && + right_type !=BTRFS_FILE_EXTENT_INLINE ) { ret =0 ; goto out; } right_disknr =btrfs_file_extent_disk_bytenr (eb, ei); - right_len =btrfs_file_extent_num_bytes (eb, ei); +if (right_type ==BTRFS_FILE_EXTENT_INLINE ) { + right_len =btrfs_file_extent_inline_len (eb, slot, ei); + right_len =PAGE_ALIGN (right_len); + }else { + right_len =btrfs_file_extent_num_bytes (eb, ei); + } right_offset =btrfs_file_extent_offset (eb, ei); right_gen =btrfs_file_extent_generation (eb, ei);
@@ -5204,6 +5210,19 @@ static int is_extent_unchanged(struct send_ctx *sctx, goto out; } +/* +* We just wanted to see if when we have an inline extent, what +* follows it is a regular extent (wanted to check the above +* condition for inline extents too). This should normally not +* happen but it's possible for example when we have an inline +* compressed extent representing data with a size matching +* the page size (currently the same as sector size). +*/ +if (right_type ==BTRFS_FILE_EXTENT_INLINE ) { + ret =0 ; + goto out; + } + left_offset_fixed = left_offset;if (key.offset < ekey->offset) {/* Fix the right offset for 2a and 7. */
Signature · 1 line
2.7.0.rc3
Quoted 22 lines · On Thu, Apr 06, 2017 at 05:07:56PM +0100, [email protected] wrote:
From: Filipe Manana <[email protected]>
Normally we don't have inline extents followed by regular extents, but there's currently at least one harmless case where this happens. For example, when the page size is 4Kb and compression is enabled:
$ mkfs.btrfs -f /dev/sdb $ mount -o compress /dev/sdb /mnt $ xfs_io -f -c "pwrite -S 0xaa 0 4K" -c "fsync" /mnt/foobar $ xfs_io -c "pwrite -S 0xbb 8K 4K" -c "fsync" /mnt/foobarIn this case we get a compressed inline extent, representing 4Kb of data, followed by a hole extent and then a regular data extent. The inline extent was not expanded/converted to a regular extent exactly because it represents 4Kb of data. This does not cause any apparent problem (such as the issue solved by commit
e1699d2d7bf6("btrfs: add missing memset while reading compressed inline extents")) except trigger an unexpected case in the incremental send code path that makes us issue an operation to write a hole when it's not needed, resulting in more writes at the receiver and wasting space at the receiver.
Quoted 5 lines
So teach the incremental send code to deal with this particular case.
The issue can be currently triggered by running fstests btrfs/137 with compression enabled (MOUNT_OPTIONS="-o compress" ./check btrfs/137).
Thanks,
-liubo
Quoted 58 lines
Signed-off-by Filipe Manana <[email protected]>--- fs/btrfs/send.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)fs/btrfs/send.c +21
-2@@ -5184,13 +5184,19 @@ static int is_extent_unchanged(struct send_ctx *sctx,while (key.offset < ekey->offset + left_len) { ei = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item); right_type =btrfs_file_extent_type (eb, ei); -if (right_type !=BTRFS_FILE_EXTENT_REG ) { +if (right_type !=BTRFS_FILE_EXTENT_REG && + right_type !=BTRFS_FILE_EXTENT_INLINE ) { ret =0 ; goto out; } right_disknr =btrfs_file_extent_disk_bytenr (eb, ei); - right_len =btrfs_file_extent_num_bytes (eb, ei); +if (right_type ==BTRFS_FILE_EXTENT_INLINE ) { + right_len =btrfs_file_extent_inline_len (eb, slot, ei); + right_len =PAGE_ALIGN (right_len); + }else { + right_len =btrfs_file_extent_num_bytes (eb, ei); + } right_offset =btrfs_file_extent_offset (eb, ei); right_gen =btrfs_file_extent_generation (eb, ei);@@ -5204,6 +5210,19 @@ static int is_extent_unchanged(struct send_ctx *sctx, goto out; } +/* +* We just wanted to see if when we have an inline extent, what +* follows it is a regular extent (wanted to check the above +* condition for inline extents too). This should normally not +* happen but it's possible for example when we have an inline +* compressed extent representing data with a size matching +* the page size (currently the same as sector size). +*/ +if (right_type ==BTRFS_FILE_EXTENT_INLINE ) { + ret =0 ; + goto out; + } + left_offset_fixed = left_offset;if (key.offset < ekey->offset) {/* Fix the right offset for 2a and 7. */ Signature · 6 lines
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