Re: [PATCH 2/9] block: update chunk_sectors in blk_stack_limits()

From: Hannes Reinecke <hare@suse.de>
To: Bart Van Assche <bart.vanassche@sandisk.com>, Jens Axboe <axboe@fb.com>
Cc: linux-block@vger.kernel.org,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Christoph Hellwig <hch@lst.de>,
	Shaun Tancheff <shaun.tancheff@seagate.com>,
	Damien Le Moal <damien.lemoal@hgst.com>,
	linux-scsi@vger.kernel.org,
	Sathya Prakash <sathya.prakash@broadcom.com>,
	Hannes Reinecke <hare@suse.com>
Subject: Re: [PATCH 2/9] block: update chunk_sectors in blk_stack_limits()
Date: Fri, 15 Apr 2016 08:05:47 +0200	[thread overview]
Message-ID: <571084BB.4020006@suse.de> (raw)
In-Reply-To: <571062E0.2010208@sandisk.com>

On 04/15/2016 05:41 AM, Bart Van Assche wrote:
> On 04/04/16 03:00, Hannes Reinecke wrote:
>> diff --git a/block/blk-settings.c b/block/blk-settings.c
>> index c7bb666..29fa900 100644
>> --- a/block/blk-settings.c
>> +++ b/block/blk-settings.c
>> @@ -630,6 +630,9 @@ int blk_stack_limits(struct queue_limits *t,
>> struct queue_limits *b,
>>               t->discard_granularity;
>>       }
>>
>> +    if (b->chunk_sectors)
>> +        t->chunk_sectors = max(t->chunk_sectors, b->chunk_sectors);
>> +
>>       return ret;
>>   }
>>   EXPORT_SYMBOL(blk_stack_limits);
> 
> Hello Hannes,
> 
> My understanding is that a non-zero chunk_sectors value defines a
> maximum I/O size. Shouldn't max() be changed into min_not_zero()?
> From include/linux/blkdev.h:
> 
> static inline unsigned int blk_max_size_offset(struct request_queue *q,
>                            sector_t offset)
> {
>     if (!q->limits.chunk_sectors)
>         return q->limits.max_sectors;
> 
>     return q->limits.chunk_sectors -
>             (offset & (q->limits.chunk_sectors - 1));
> }
> 
Hmm.

_Actually_ it should be the least common denominator, me thinks...
Have to think it through a bit more.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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