[PATCH 02/21] block: Limit atomic writes according to bio and queue limits

John Garry
2023-09-29T10:28:27Z

We rely the block layer always being able to send a bio of size
atomic_write_unit_max without being required to split it due to request
queue or other bio limits.

A bio may contain min(BIO_MAX_VECS, limits->max_segments) vectors,
and each vector is at worst case the device logical block size from
direct IO alignment requirement.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
block/blk-settings.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index d151be394c98..57d487a00c64 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -213,6 +213,18 @@ void blk_queue_atomic_write_boundary_bytes(struct request_queue *q,
}
EXPORT_SYMBOL(blk_queue_atomic_write_boundary_bytes);

+static unsigned int blk_queue_max_guaranteed_bio_size_sectors(
+ struct request_queue *q)
+{
+ struct queue_limits *limits = &q->limits;
+ unsigned int max_segments = min_t(unsigned int, BIO_MAX_VECS,
+ limits->max_segments);
+ /* Limit according to dev sector size as we only support direct-io */
+ unsigned int limit = max_segments * queue_logical_block_size(q);
+
+ return rounddown_pow_of_two(limit >> SECTOR_SHIFT);
+}
+
/**
* blk_queue_atomic_write_unit_min_sectors - smallest unit that can be written
* atomically to the device.
@@ -223,8 +235,10 @@ void blk_queue_atomic_write_unit_min_sectors(struct request_queue *q,
unsigned int sectors)
{
struct queue_limits *limits = &q->limits;
+ unsigned int guaranteed_sectors =
+ blk_queue_max_guaranteed_bio_size_sectors(q);

- limits->atomic_write_unit_min_sectors = sectors;
+ limits->atomic_write_unit_min_sectors = min(guaranteed_sectors, sectors);
}
EXPORT_SYMBOL(blk_queue_atomic_write_unit_min_sectors);

@@ -238,8 +252,10 @@ void blk_queue_atomic_write_unit_max_sectors(struct request_queue *q,
unsigned int sectors)
{
struct queue_limits *limits = &q->limits;
+ unsigned int guaranteed_sectors =
+ blk_queue_max_guaranteed_bio_size_sectors(q);

- limits->atomic_write_unit_max_sectors = sectors;
+ limits->atomic_write_unit_max_sectors = min(guaranteed_sectors, sectors);
}
EXPORT_SYMBOL(blk_queue_atomic_write_unit_max_sectors);

--
2.31.1