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

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Date:	Mon, 15 Feb 2016 18:27:09 +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 Mon, Feb 15, 2016 at 4:22 PM, 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))
>>                 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.

>
> bvec_gap_to_prev is already checking the virt_boundary and I'd sorta
> like to keep the motivation to optimize bio_get_last_bvec() to be O(1).

Currently the approaches I thought of still need to iterate bvec by bvec,
not sure if O(1) can be reached easily, but I am happy to discuss the
optimized implementation.

Thanks,
Ming