Re: [PATCH v3 1/9] block: Introduce QUEUE_FLAG_SUB_PAGE_SEGMENTS and CONFIG_BLK_SUB_PAGE_SEGMENTS

[Bart Van Assche <bvanassche@acm.org>]

On 1/18/23 15:02, Jens Axboe wrote:
> On 1/18/23 3:54 PM, Bart Van Assche wrote:
>> Prepare for introducing support for segments smaller than the page size
>> by introducing the request queue flag QUEUE_FLAG_SUB_PAGE_SEGMENTS.
>> Introduce CONFIG_BLK_SUB_PAGE_SEGMENTS to prevent that performance of
>> block drivers that support segments >= PAGE_SIZE would be affected.
>>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Ming Lei <ming.lei@redhat.com>
>> Cc: Keith Busch <kbusch@kernel.org>
>> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
>> ---
>>   block/Kconfig          | 9 +++++++++
>>   include/linux/blkdev.h | 7 +++++++
>>   2 files changed, 16 insertions(+)
>>
>> diff --git a/block/Kconfig b/block/Kconfig
>> index 5d9d9c84d516..e85061d2175b 100644
>> --- a/block/Kconfig
>> +++ b/block/Kconfig
>> @@ -35,6 +35,15 @@ config BLOCK_LEGACY_AUTOLOAD
>>   	  created on demand, but scripts that manually create device nodes and
>>   	  then call losetup might rely on this behavior.
>>   
>> +config BLK_SUB_PAGE_SEGMENTS
>> +       bool "Support segments smaller than the page size"
>> +       default n
>> +       help
>> +	  Most storage controllers support DMA segments larger than the typical
>> +	  size of a virtual memory page. Some embedded controllers only support
>> +	  DMA segments smaller than the page size. Enable this option to support
>> +	  such controllers.
> 
> This should not be a visible option at all, affected drivers should just
> select it.

Hi Jens,

Thanks for the feedback. Unless anyone requests me to realize this in another
way, I plan to merge the patch below into the patch above:


diff --git a/block/Kconfig b/block/Kconfig
index e85061d2175b..b44b449c47bf 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -36,13 +36,7 @@ config BLOCK_LEGACY_AUTOLOAD
  	  then call losetup might rely on this behavior.

  config BLK_SUB_PAGE_SEGMENTS
-       bool "Support segments smaller than the page size"
-       default n
-       help
-	  Most storage controllers support DMA segments larger than the typical
-	  size of a virtual memory page. Some embedded controllers only support
-	  DMA segments smaller than the page size. Enable this option to support
-	  such controllers.
+       bool

  config BLK_RQ_ALLOC_TIME
  	bool