[PATCH] block: Increase BLK_DEF_MAX_SECTORS_CAP

[Damien Le Moal <dlemoal@kernel.org>]

Back in 2015, commit d2be537c3ba3 ("block: bump BLK_DEF_MAX_SECTORS to
2560") increased the default maximum size of a block device I/O to 2560
sectors (1280 KiB) to "accommodate a 10-data-disk stripe write with
chunk size 128k". This choice is rather arbitrary and since then,
improvements to the block layer have software RAID drivers correctly
advertize their stripe width through chunk_sectors and abuses of
BLK_DEF_MAX_SECTORS_CAP by drivers (to set the HW limit rather than the
default user controlled maximum I/O size) have been fixed.

Since many block devices can benefit from a larger value of
BLK_DEF_MAX_SECTORS_CAP, and in particular HDDs, increase this value to
be 4MiB, or 8192 sectors.

Suggested-by: Martin K . Petersen <martin.petersen@oracle.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
 include/linux/blkdev.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 85aab8bc96e7..7c35b2462048 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1238,7 +1238,7 @@ enum blk_default_limits {
  * Not to be confused with the max_hw_sector limit that is entirely
  * controlled by the driver, usually based on hardware limits.
  */
-#define BLK_DEF_MAX_SECTORS_CAP	2560u
+#define BLK_DEF_MAX_SECTORS_CAP	8192u
 
 static inline struct queue_limits *bdev_limits(struct block_device *bdev)
 {
-- 
2.49.0