linux-kernel - Re: [PATCH 2/5] block: add request->io_data

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Date:   Wed, 8 Apr 2020 22:11:19 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...r.kernel.org,
        cgroups@...r.kernel.org, newella@...com, josef@...icpanda.com
Subject: Re: [PATCH 2/5] block: add request->io_data_len

On Thu, Apr 09, 2020 at 09:44:06AM +0800, Ming Lei wrote:
> Almost all __blk_mq_end_request() follow blk_update_request(), so the
> completed bytes can be passed to __blk_mq_end_request(), then we can
> avoid to introduce this field.

But on some drivers blk_update_request() may be called multiple times before
__blk_mq_end_request() is called and what's needed here is the total number of
bytes in the whole request, not just in the final completion.

> Also there is just 20 callers of __blk_mq_end_request(), looks this kind
> of change shouldn't be too big.

This would work iff we get rid of partial completions and if we get rid of
partial completions, we might as well stop exposing blk_update_request() and
__blk_mq_end_request().

Thanks.

-- 
tejun