Re: [PATCH v4 4/7] block: introduce write-hint to stream-id conversion

From: Jens Axboe
Date: Wed Apr 17 2019 - 13:57:56 EST

On 4/17/19 11:50 AM, Kanchan Joshi wrote:
> This patch moves write-hint-to-stream-id conversion in block-layer.
> Earlier this was done by driver (nvme). Current conversion is of the
> form "streamid = write-hint - 1", for both user and kernel streams.
> Conversion takes stream limit (maintained in request queue) into
> account. Write-hints beyond the exposed limit turn to 0.
> A new field 'streamid' has been added in request. While 'write-hint'
> field continues to exist. It keeps original value passed from upper
> layer, and used during merging checks.

Why not just use the bio write hint? We already disallow merging of
dissimilar write hints, so req->bio->bi_write_hint is known to be
identical with the rest of the bio's in that chain.

Jens Axboe