linux-kernel - Re: [PATCH 2/4] block: check virt boundary in bio_will

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Date:	Tue, 16 Feb 2016 21:08:58 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Sagi Grimberg <sagig@....mellanox.co.il>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 2/4] block: check virt boundary in bio_will_gap()

On Tue, Feb 16, 2016 at 4:27 AM, Sagi Grimberg <sagig@....mellanox.co.il> wrote:
>
>>>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>>>> index 4571ef1..b8ff6a3 100644
>>>> --- a/include/linux/blkdev.h
>>>> +++ b/include/linux/blkdev.h
>>>> @@ -1388,7 +1388,7 @@ static inline bool bvec_gap_to_prev(struct
>>>> request_queue *q,
>>>>    static inline bool bio_will_gap(struct request_queue *q, struct bio
>>>> *prev,
>>>>                           struct bio *next)
>>>>    {
>>>> -       if (!bio_has_data(prev))
>>>> +       if (!bio_has_data(prev) || !queue_virt_boundary(q))
>>>>    bio_integrity_add_page              return false;
>>>
>>>
>>>
>>> Can we not do that?
>>
>>
>> Given there are only 3 drivers which set virt boundary, I think
>> it is reasonable to do that.
>
>
> 3 drivers that are really performance critical. I don't think we
> should add optimized branching for some of the drivers especially
> when the drivers that do set virt_boundary *really* care about latency.

I don't think the extra check on bvec_gap_to_prev() can make any
difference, but if you do care we can introduce __bvec_gap_to_prev()
in which the check is moved into bio_will_gap().

Thanks,