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@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Keith Busch <kbusch@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
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,
If CONFIG_BLK_SUB_PAGE_SEGMENTS is made invisible, how should this
option be enabled for the scsi_debug and null_blk drivers? Adding
"select BLK_SUB_PAGE_SEGMENTS" to the Kconfig section of these drivers
would have the unfortunate side effect that enabling either driver would
make all block drivers slower. How about making sub-page segment support
configurable for the scsi_debug and null_blk drivers only? That would
allow kernel developers who want to test the sub-page segment support to
enable this functionality without making e.g. distro kernels slower.
Thanks,
Bart.
