linux-kernel - Re: [PATCH next 3/4] blk-mq: user (1 << order) to implement order_to

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Date:	Fri, 18 Apr 2014 21:23:49 +0200
From:	Jörg-Volker Peetz <jvpeetz@....de>
To:	Ming Lei <tom.leiming@...il.com>
CC:	Jens Axboe <axboe@...nel.dk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH next 3/4] blk-mq: user (1 << order) to implement order_to_size()

Ming Lei wrote, on 04/18/2014 17:47:
> On Fri, Apr 18, 2014 at 3:03 AM, Jörg-Volker Peetz <jvpeetz@....de> wrote:
>> Ming Lei wrote, on 04/17/2014 17:49:
>>> Signed-off-by: Ming Lei <tom.leiming@...il.com>
>>> ---
>>>  block/blk-mq.c |    7 +------
>>>  1 file changed, 1 insertion(+), 6 deletions(-)
>>>
>>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>>> index baff2d0..1eff3d9 100644
>>> --- a/block/blk-mq.c
>>> +++ b/block/blk-mq.c
>>> @@ -1130,12 +1130,7 @@ static void blk_mq_free_rq_map(struct blk_mq_tag_set *set,
>>>
>>>  static size_t order_to_size(unsigned int order)
>>>  {
>>> -     size_t ret = PAGE_SIZE;
>>> -
>>> -     while (order--)
>>> -             ret *= 2;
>>> -
>>> -     return ret;
>>> +     return (1 << order) * PAGE_SIZE;
>>
>> Shouldn't this be
>>
>>         return ((size_t)1 << order) * PAGE_SIZE;
>>
>> ?
> 
> IMO, it isn't necessary since compiler will cast type
> of 1 and the expression to size_t automatically.
> 
> 
> Thanks,

Testing this with gcc 4.8.2 with order > 30 confirms that the automatic casting
is done operator-wise and the explicit casting is necessary.

Regards,
jvp.

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