On 4/15/21 3:38 AM, Changheun Lee wrote:

quoted

@@ -167,6 +168,7 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
 	max_sectors = round_down(max_sectors,
 				 limits->logical_block_size >> SECTOR_SHIFT);
 	limits->max_sectors = max_sectors;
+	limits->bio_max_bytes = max_sectors << SECTOR_SHIFT;
 
 	q->backing_dev_info->io_pages = max_sectors >> (PAGE_SHIFT - 9);
 }

Can the new shift operation overflow? If so, how about using
check_shl_overflow()?

OK, I'll check.

quoted

@@ -538,6 +540,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 {
 	unsigned int top, bottom, alignment, ret = 0;
 
+	t->bio_max_bytes = min_not_zero(t->bio_max_bytes, b->bio_max_bytes);
+
 	t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
 	t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
 	t->max_dev_sectors = min_not_zero(t->max_dev_sectors, b->max_dev_sectors);

The above will limit bio_max_bytes for all stacked block devices, which
is something we do not want. I propose to set t->bio_max_bytes to
UINT_MAX in blk_stack_limits() and to let the stacked driver (e.g.
dm-crypt) decide whether or not to lower that value.

Actually, bio size should be limited in dm-crypt too. Because almost I/O
from user space will be gone to dm-crypt first. I/O issue timing will be
delayed if bio size is not limited in dm-crypt.
Do you have any idea to decide whether takes lower bio max size, or not
in the stacked driver?
Add a flag to decide this in driver layer like before?
Or insert code manually in each stacked driver if it is needed?

quoted

diff --git a/include/linux/bio.h b/include/linux/bio.h
index d0246c92a6e8..e5add63da3af 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h

@@ -106,6 +106,8 @@ static inline void *bio_data(struct bio *bio)
 	return NULL;
 }
 
+extern unsigned int bio_max_size(struct bio *bio);

You may want to define bio_max_size() as an inline function in bio.h
such that no additional function calls are introduced in the hot path.

Thanks, I'll try.

Thanks,

Bart.