Information about continuous extent placement may be useful for some block devices. Say, distributed network filesystems, which provide block device interface, may use this information for better blocks placement over the nodes in their cluster, and for better performance. Block devices, which map a file on another filesystem (loop), may request the same length extent on underlining filesystem for less fragmentation and for batching allocation requests. Also, hypervisors like QEMU may use this information for optimization of cluster allocations. This patchset introduces REQ_OP_ASSIGN_RANGE, which is going to be used for forwarding user's fallocate(0) requests into block device internals. It rather similar to existing REQ_OP_DISCARD, REQ_OP_WRITE_ZEROES, etc. The corresponding exported primitive is called blkdev_issue_assign_range(). See [1/3] for the details. Patch [2/3] teaches loop driver to handle REQ_OP_ASSIGN_RANGE requests by calling fallocate(0). Patch [3/3] makes ext4 to notify a block device about fallocate(0). Here is a simple test I did: https://gist.github.com/tkhai/5b788651cdb74c1dbff3500745878856 I attached a file on ext4 to loop. Then, created ext4 partition on loop device and started the test in the partition. Direct-io is enabled on loop. The test fallocates 4G file and writes from some offset with given step, then it chooses another offset and repeats. After the test all the blocks in the file become written. The results shows that batching extents-assigning requests improves the performance: Before patchset: real ~ 1min 27sec After patchset: real ~ 1min 16sec (18% better) Ordinary fallocate() before writes improves the performance by batching the requests. These results just show, the same is in case of forwarding extents information to underlining filesystem. --- Kirill Tkhai (3): block: Add support for REQ_OP_ASSIGN_RANGE operation loop: Forward REQ_OP_ASSIGN_RANGE into fallocate(0) ext4: Notify block device about fallocate(0)-assigned blocks block/blk-core.c | 4 +++ block/blk-lib.c | 70 +++++++++++++++++++++++++++++++++++++++++++++ block/blk-merge.c | 21 ++++++++++++++ block/bounce.c | 1 + drivers/block/loop.c | 5 +++ fs/ext4/ext4.h | 1 + fs/ext4/extents.c | 11 ++++++- include/linux/bio.h | 3 ++ include/linux/blk_types.h | 2 + include/linux/blkdev.h | 29 +++++++++++++++++++ 10 files changed, 145 insertions(+), 2 deletions(-) -- Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
