[PATCH RFC 06/16] block: Limit atomic writes according to bio and queue limits
From: John Garry <john.g.garry@oracle.com>
Date: 2023-05-03 18:40:34
Also in:
linux-block, linux-fsdevel, linux-nvme, linux-scsi, linux-xfs, lkml
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
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. We already know at any bio should have an alignment of atomic_write_unit_max or lower. A bio may contain min(BIO_MAX_VECS, limits->max_segments) vectors, and each vector of at least PAGE_SIZE, except for if start address may not be PAGE aligned; for this case, subtract 1 to give the max guaranteed count of pages which we may store in a bio, and limit both atomic_write_unit_min and atomic_write_unit_max to this value. Signed-off-by: John Garry <john.g.garry@oracle.com> --- block/blk-settings.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-)
diff --git a/block/blk-settings.c b/block/blk-settings.c
index e21731715a12..f64a2f736cb8 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c@@ -212,6 +212,18 @@ void blk_queue_atomic_write_boundary(struct request_queue *q, } EXPORT_SYMBOL(blk_queue_atomic_write_boundary); +static unsigned int blk_queue_max_guaranteed_bio_size(struct queue_limits *limits) +{ + unsigned int max_segments = limits->max_segments; + unsigned int atomic_write_max_segments = + min(BIO_MAX_VECS, max_segments); + /* subtract 1 to assume PAGE-misaligned IOV start address */ + unsigned int size = (atomic_write_max_segments - 1) * + (PAGE_SIZE / SECTOR_SIZE); + + return rounddown_pow_of_two(size); +} + /** * blk_queue_atomic_write_unit_min - smallest unit that can be written * atomically to the device.
@@ -221,7 +233,10 @@ EXPORT_SYMBOL(blk_queue_atomic_write_boundary); void blk_queue_atomic_write_unit_min(struct request_queue *q, unsigned int sectors) { - q->limits.atomic_write_unit_min = sectors; + struct queue_limits *limits= &q->limits; + unsigned int guaranteed = blk_queue_max_guaranteed_bio_size(limits); + + limits->atomic_write_unit_min = min(guaranteed, sectors); } EXPORT_SYMBOL(blk_queue_atomic_write_unit_min);
@@ -234,8 +249,10 @@ EXPORT_SYMBOL(blk_queue_atomic_write_unit_min); void blk_queue_atomic_write_unit_max(struct request_queue *q, unsigned int sectors) { - struct queue_limits *limits = &q->limits; - limits->atomic_write_unit_max = sectors; + struct queue_limits *limits= &q->limits; + unsigned int guaranteed = blk_queue_max_guaranteed_bio_size(limits); + + limits->atomic_write_unit_max = min(guaranteed, sectors); } EXPORT_SYMBOL(blk_queue_atomic_write_unit_max);
--
2.31.1