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

[Kirill Tkhai]

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@xxxxxxxxxxxxx>
>