bio_discard_limit() enforces discard boundaries within the range of 32-bit
unsigned integers, resulting in unexpected discard cut boundaries.

For example, max discard size = 1MiB, discard_granularity = 512B, then the
discard lengths sent in the range [0,4G) are 1MiB, 1MiB... (1MiB-512).
The next discard offset from 4G is [4G-512, 4G-512+1MiB).
The discard of the 4G offset boundary does not comply with the optimal 1MiB
size.

Signed-off-by: Li Feng <fengli@smartx.com>
---
 block/blk-lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index e59c3069e835..ec95508c3593 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -32,7 +32,7 @@ static sector_t bio_discard_limit(struct block_device *bdev, sector_t sector)
 	 * Align the bio size to the discard granularity to make splitting the bio
 	 * at discard granularity boundaries easier in the driver if needed.
 	 */
-	return round_down(UINT_MAX, discard_granularity) >> SECTOR_SHIFT;
+	return round_down(ULONG_MAX, discard_granularity) >> SECTOR_SHIFT;
 }
 
 int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
-- 
2.41.0

On Thu, Aug 17, 2023 at 3:42 PM Li Feng <fengli@smartx.com> wrote:
>
> bio_discard_limit() enforces discard boundaries within the range of 32-bit
> unsigned integers, resulting in unexpected discard cut boundaries.

Any bio size can't be bigger than UINT_MAX, see bio definition.

>
> For example, max discard size = 1MiB, discard_granularity = 512B, then the
> discard lengths sent in the range [0,4G) are 1MiB, 1MiB... (1MiB-512).
> The next discard offset from 4G is [4G-512, 4G-512+1MiB).
> The discard of the 4G offset boundary does not comply with the optimal 1MiB
> size.

As mentioned, max bio size is 4GB, so there shouldn't be such issue.

Thanks,

> 2023年8月22日 21:07，Ming Lei <ming.lei@redhat.com> 写道：
> 
> On Thu, Aug 17, 2023 at 3:42 PM Li Feng <fengli@smartx.com> wrote:
>> 
>> bio_discard_limit() enforces discard boundaries within the range of 32-bit
>> unsigned integers, resulting in unexpected discard cut boundaries.
> 
> Any bio size can't be bigger than UINT_MAX, see bio definition.
> 
>> 
>> For example, max discard size = 1MiB, discard_granularity = 512B, then the
>> discard lengths sent in the range [0,4G) are 1MiB, 1MiB... (1MiB-512).
>> The next discard offset from 4G is [4G-512, 4G-512+1MiB).
>> The discard of the 4G offset boundary does not comply with the optimal 1MiB
>> size.
> 
> As mentioned, max bio size is 4GB, so there shouldn't be such issue.
> 
> Thanks,
> 
Got it, many thanks.

Ping…

Thanks,
Li

> 2023年8月17日 下午3:55，Li Feng <fengli@smartx.com> 写道：
> 
> bio_discard_limit() enforces discard boundaries within the range of 32-bit
> unsigned integers, resulting in unexpected discard cut boundaries.
> 
> For example, max discard size = 1MiB, discard_granularity = 512B, then the
> discard lengths sent in the range [0,4G) are 1MiB, 1MiB... (1MiB-512).
> The next discard offset from 4G is [4G-512, 4G-512+1MiB).
> The discard of the 4G offset boundary does not comply with the optimal 1MiB
> size.
> 
> Signed-off-by: Li Feng <fengli@smartx.com>
> ---
> block/blk-lib.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index e59c3069e835..ec95508c3593 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -32,7 +32,7 @@ static sector_t bio_discard_limit(struct block_device *bdev, sector_t sector)
> 	 * Align the bio size to the discard granularity to make splitting the bio
> 	 * at discard granularity boundaries easier in the driver if needed.
> 	 */
> -	return round_down(UINT_MAX, discard_granularity) >> SECTOR_SHIFT;
> +	return round_down(ULONG_MAX, discard_granularity) >> SECTOR_SHIFT;
> }
> 
> int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> -- 
> 2.41.0
>