Re: [PATCH 01/21] block: Add atomic write operations to request_queue limits

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On 09/11/2023 15:10, Christoph Hellwig wrote:
Documentation/ABI/stable/sysfs-block | 42 +++++++++++++++++++
  block/blk-settings.c                 | 60 ++++++++++++++++++++++++++++
  block/blk-sysfs.c                    | 33 +++++++++++++++
  include/linux/blkdev.h               | 33 +++++++++++++++
  4 files changed, 168 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index 1fe9a553c37b..05df7f74cbc1 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -21,6 +21,48 @@ Description:
  		device is offset from the internal allocation unit's
  		natural alignment.
+What: /sys/block/<disk>/atomic_write_max_bytes
+Date:		May 2023
+Contact:	Himanshu Madhani<himanshu.madhani@xxxxxxxxxx>
+Description:
+		[RO] This parameter specifies the maximum atomic write
+		size reported by the device. An atomic write operation
+		must not exceed this number of bytes.
+What:		/sys/block/<disk>/atomic_write_unit_max_bytes
+Date:		January 2023
+Contact:	Himanshu Madhani<himanshu.madhani@xxxxxxxxxx>
+Description:
+		[RO] This parameter defines the largest block which can be
+		written atomically with an atomic write operation. This
+		value must be a multiple of atomic_write_unit_min and must
+		be a power-of-two.
What is the difference between these two values?

Generally they come from the same device property. Then since atomic_write_unit_max_bytes must be a power-of-2 (and atomic_write_max_bytes may not be), they may be different. In addition, atomic_write_unit_max_bytes is required to be limited by whatever is guaranteed to be able to fit in a bio.

atomic_write_max_bytes is really only relevant for merging writes. Maybe we should not even expose via sysfs.

BTW, I do still wonder whether all these values should be limited by max_sectors_kb (which they aren't currently).



+Date:		May 2023
+Contact:	Himanshu Madhani<himanshu.madhani@xxxxxxxxxx>
+Description:
+		[RO] This parameter specifies the smallest block which can
+		be written atomically with an atomic write operation. All
+		atomic write operations must begin at a
+		atomic_write_unit_min boundary and must be multiples of
+		atomic_write_unit_min. This value must be a power-of-two.
How can the minimum unit be anythіng but one logical block?

+extern void blk_queue_atomic_write_max_bytes(struct request_queue *q,
+					     unsigned int bytes);
Please don't add pointless externs to prototypes in headers.

ok, fine - blkdev.h seems to have a mix for declarations with and without extern, so at least we would be consistently inconsistent.


+static inline unsigned int queue_atomic_write_unit_max_bytes(const struct request_queue *q)
.. and please avoid the overly long lines.

ok

Thanks,
John







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