Some SATA SSDs and most NVMe SSDs report physical block size 512 bytes,
but they use 4K remapping table internally and they do slow
read-modify-write cycle for requests that are not aligned on 4K boundary.
Therefore, io_opt should be aligned on 4K.
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
Fixes: a23634644afc ("block: take io_opt and io_min into account for
max_sectors")
Fixes: 9c0ba14828d6 ("blk-settings: round down io_opt to physical_block_size")
Cc: sta...@vger.kernel.org # v6.11+
---
block/blk-settings.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
Index: linux-2.6/block/blk-settings.c
===================================================================
--- linux-2.6.orig/block/blk-settings.c 2025-01-03 21:10:56.000000000 +0100
+++ linux-2.6/block/blk-settings.c 2025-01-20 15:59:13.000000000 +0100
@@ -269,8 +269,12 @@ int blk_validate_limits(struct queue_lim
* The optimal I/O size may not be aligned to physical block size
* (because it may be limited by dma engines which have no clue about
* block size of the disks attached to them), so we round it down here.
+ *
+ * Note that some SSDs erroneously report physical_block_size 512
+ * despite the fact that they have remapping table granularity 4K and
+ * they perform read-modify-write for unaligned requests.
*/
- lim->io_opt = round_down(lim->io_opt, lim->physical_block_size);
+ lim->io_opt = round_down(lim->io_opt, max(4096,
lim->physical_block_size));
/*
* max_hw_sectors has a somewhat weird default for historical reason,
