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SubjectRe: [PATCH RFC 0/3] block,ext4: Introduce REQ_OP_ASSIGN_RANGE to reflect extents allocation in block device internals
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Hi!

Any comments on this?

Thanks

On 10.12.2019 19:56, Kirill Tkhai wrote:
> 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@virtuozzo.com>
>

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