Re: [PATCH 11/19] btrfs: introduce submit buffer

[Josef Bacik]

On Fri, Jun 07, 2019 at 10:10:17PM +0900, Naohiro Aota wrote:
> Sequential allocation is not enough to maintain sequential delivery of
> write IOs to the device. Various features (async compress, async checksum,
> ...) of btrfs affect ordering of the IOs. This patch introduces submit
> buffer to sort WRITE bios belonging to a block group and sort them out
> sequentially in increasing block address to achieve sequential write
> sequences with __btrfs_map_bio().
> 
> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>

I hate everything about this.  Can't we just use the plugging infrastructure for
this and then make sure it re-orders the bios before submitting them?  Also
what's to prevent the block layer scheduler from re-arranging these io's?
Thanks,

Josef