On Mon, Nov 06, 2023 at 12:53:31PM +0800, Ming Lei wrote:
> 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:
The following one fixes several bugs, and is verified to be capable of
making big & aligned bios, feel free to run your test against this one:
block/bio.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/block/bio.c b/block/bio.c
index 816d412c06e9..80b36ce57510 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1211,6 +1211,7 @@ static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page,
}
#define PAGE_PTRS_PER_BVEC (sizeof(struct bio_vec) / sizeof(struct page *))
+#define BIO_CHUNK_SIZE (256U << 10)
/**
* __bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
@@ -1266,6 +1267,31 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
size -= trim;
}
+ /*
+ * Try to make bio aligned with 128KB if it isn't the last one, so
+ * we can avoid small bio in case of big chunk sequential IO because
+ * of bio split and multipage bvec.
+ *
+ * If nothing is added to this bio, simply allow unaligned since we
+ * have chance to add more bytes
+ */
+ if (iov_iter_count(iter) && bio->bi_iter.bi_size) {
+ unsigned int aligned_size = (bio->bi_iter.bi_size + size) &
+ ~(BIO_CHUNK_SIZE - 1);
+
+ if (aligned_size <= bio->bi_iter.bi_size) {
+ /* stop to add page if this bio can't keep aligned */
+ if (!(bio->bi_iter.bi_size & (BIO_CHUNK_SIZE - 1))) {
+ ret = left = size;
+ goto revert;
+ }
+ } else {
+ aligned_size -= bio->bi_iter.bi_size;
+ iov_iter_revert(iter, size - aligned_size);
+ size = aligned_size;
+ }
+ }
+
if (unlikely(!size)) {
ret = -EFAULT;
goto out;
@@ -1285,7 +1311,7 @@ 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)
--
2.41.0
Thanks,
Ming
