Re: [PATCH 1/1] block: Check the queue limit before bio submitting

[Ming Lei <ming.lei@redhat.com>]

On Mon, Nov 06, 2023 at 01:40:12AM +0000, Ed Tsai (蔡宗軒) wrote:
> On Mon, 2023-11-06 at 09:33 +0800, Ed Tsai wrote:
> > On Sat, 2023-11-04 at 11:43 +0800, Ming Lei wrote:

...

> Sorry for missing out on my dd command. Here it is:
> dd if=/data/test_file of=/dev/null bs=64m count=1 iflag=direct

OK, thanks for the sharing.

I understand the issue now, but not sure if it is one good idea to check
queue limit in __bio_iov_iter_get_pages():

1) bio->bi_bdev may not be set

2) what matters is actually bio's alignment, and bio size still can
be big enough

So I cooked one patch, and it should address your issue:


diff --git a/block/bio.c b/block/bio.c
index 816d412c06e9..7d982e74c65d 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1266,6 +1266,24 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 		size -= trim;
 	}
 
+	/*
+	 * Try to make bio aligned with 128KB if there are pages left so we
+	 * can avoid small bio in case of big chunk sequential IO
+	 */
+	if (iov_iter_count(iter)) {
+		unsigned curr_size = (bio->bi_iter.bi_size + size) &
+			~((128U << 10) - 1);
+		if (curr_size <= bio->bi_iter.bi_size) {
+			ret = left = size;
+			goto revert;
+		} else {
+			curr_size -= bio->bi_iter.bi_size;
+			ret = size - curr_size;
+			iov_iter_revert(iter, ret);
+			size = curr_size;
+		}
+	}
+
 	if (unlikely(!size)) {
 		ret = -EFAULT;
 		goto out;
@@ -1285,7 +1303,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 
 		offset = 0;
 	}
-
+revert:
 	iov_iter_revert(iter, left);
 out:
 	while (i < nr_pages)




Thanks,
Ming