Re: [PATCH 1/1] block: move the PAGE_SECTORS definition into <linux/blkdev.h>

[Leizhen (ThunderTown)]

On 8/21/2020 12:11 PM, Coly Li wrote:
> On 2020/8/21 10:03, Zhen Lei wrote:
>> There are too many PAGE_SECTORS definitions, and all of them are the
>> same. It looks a bit of a mess. So why not move it into <linux/blkdev.h>,
>> to achieve a basic and unique definition.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> 
> 
> A lazy question about page size > 4KB: currently in bcache code the
> sector size is assumed to be 512 sectors, if kernel page > 4KB, it is
> possible that PAGE_SECTORS in bcache will be a number > 8 ?

Sorry, I don't fully understand your question. I known that the sector size
can be 512 or 4K, and the PAGE_SIZE can be 4K or 64K. So even if sector size
is 4K, isn't it greater than 8 for 64K pages?

I'm not sure if the question you're asking is the one Matthew Wilcox has
answered before:
https://www.spinics.net/lists/raid/msg64345.html

> 
> Thanks.
> 
> Coly Li
> 
> 
>> ---
>>  drivers/block/brd.c           | 1 -
>>  drivers/block/null_blk_main.c | 1 -
>>  drivers/md/bcache/util.h      | 2 --
>>  include/linux/blkdev.h        | 5 +++--
>>  include/linux/device-mapper.h | 1 -
>>  5 files changed, 3 insertions(+), 7 deletions(-)
>>
> 
> [snipped]
> 
>> diff --git a/drivers/md/bcache/util.h b/drivers/md/bcache/util.h
>> index c029f7443190805..55196e0f37c32c6 100644
>> --- a/drivers/md/bcache/util.h
>> +++ b/drivers/md/bcache/util.h
>> @@ -15,8 +15,6 @@
>>  
>>  #include "closure.h"
>>  
>> -#define PAGE_SECTORS		(PAGE_SIZE / 512)
>> -
>>  struct closure;
>>  
>>  #ifdef CONFIG_BCACHE_DEBUG
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index bb5636cc17b91a7..b068dfc5f2ef0ab 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -949,11 +949,12 @@ static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
>>   * multiple of 512 bytes. Hence these two constants.
>>   */
>>  #ifndef SECTOR_SHIFT
>> -#define SECTOR_SHIFT 9
>> +#define SECTOR_SHIFT		9
>>  #endif
>>  #ifndef SECTOR_SIZE
>> -#define SECTOR_SIZE (1 << SECTOR_SHIFT)
>> +#define SECTOR_SIZE		(1 << SECTOR_SHIFT)
>>  #endif
>> +#define PAGE_SECTORS		(PAGE_SIZE / SECTOR_SIZE)
>>  
>>  /*
>>   * blk_rq_pos()			: the current sector
> [snipped]
> 
>