On Sat, Feb 15, 2025 at 3:51 AM David Laight
[off-list ref] wrote:

On Fri, 14 Feb 2025 12:36:36 -0700
Caleb Sander Mateos [off-list ref] wrote:

quoted

In bvec_split_segs(), max_bytes is an unsigned, so it must be less than
or equal to UINT_MAX. Remove the unnecessary min().

Prior to commit 67927d220150 ("block/merge: count bytes instead of
sectors"), the min() was with UINT_MAX >> 9, so it did have an effect.

Signed-off-by: Caleb Sander Mateos <redacted>
---
 block/blk-merge.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 15cd231d560c..39b738c0e4c9 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c

@@ -268,11 +268,11 @@ static inline unsigned get_max_segment_size(const struct queue_limits *lim,
  */
 static bool bvec_split_segs(const struct queue_limits *lim,
              const struct bio_vec *bv, unsigned *nsegs, unsigned *bytes,
              unsigned max_segs, unsigned max_bytes)
 {
-     unsigned max_len = min(max_bytes, UINT_MAX) - *bytes;
+     unsigned max_len = max_bytes - *bytes;

More interestingly, what stops *bytes being larger than max_bytes?

bvec_split_segs() has two callers, bio_split_rw_at() and
blk_recalc_rq_segments(). In both, *bytes = 0 originally.
bio_split_rw_at() has another code path which increments *bytes, but
it makes sure not to exceed max_bytes. So when bvec_split_segs() is
called, *bytes <= max_bytes. The logic in bvec_split_segs() won't
increment *bytes by more than len, which is at most max_len =
max_bytes - *bytes. So inductively, *bytes <= max_bytes before every
call to bvec_split_segs().

        David

quoted

      unsigned len = min(bv->bv_len, max_len);
      unsigned total_len = 0;
      unsigned seg_size = 0;

      while (len && *nsegs < max_segs) {