[PATCH 0/2] Allow deduplication of the eof block when it is safe to do so

fdmanana
2019-12-16T18:27:33Z

From: Filipe Manana <fdmanana@suse.com>

Hi,

This short series allows deduplication of the last block of a file when
the eof is not aligned to the sector size, as long as the range's end
offset matches the eof of the destination file.

This is a safe case unlike the case where we attempt to clone the block in
the middle of a file (which results in a corruption I found last year and
affected both btrfs and xfs).

This is motivated by btrfs users reporting lower deduplication scores
starting with kernel 5.0, which was the kernel release where btrfs was
changed to use the generic VFS helper generic_remap_file_range_prep().
Users observed that the last block was no longer deduplicated when a
file's size is not block size aligned. For btrfs this is specially
important because references are kept per extent and not per block, so
not having the last block deduplicated means the entire extent is kept
allocated, making the deduplication not effective and often pointless in
many cases.

Thanks.

Filipe Manana (2):
fs: allow deduplication of eof block into the end of the destination
file
Btrfs: make deduplication with range including the last block work

fs/btrfs/ioctl.c | 3 ++-
fs/read_write.c | 10 ++++------
2 files changed, 6 insertions(+), 7 deletions(-)

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2.11.0