linux-ext4 - Re: [PATCH v4 4/7] block: introduce write-hint to stream-id conversion

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Message-ID: <6850a3ad-805f-4232-1bc7-f3249e1fba96@kernel.dk>
Date:   Wed, 17 Apr 2019 11:57:50 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Kanchan Joshi <joshi.k@...sung.com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Cc:     prakash.v@...sung.com
Subject: Re: [PATCH v4 4/7] block: introduce write-hint to stream-id
 conversion

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