Re: [PATCHv2 1/3] block/bio: remove duplicate append pages code

[Christoph Hellwig <hch@lst.de>]

On Wed, May 18, 2022 at 10:11:29AM -0700, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
> 
> The setup for getting pages are identical for zone append and normal IO.
> Use common code for each.

How about using even more common code and avoiding churn at the same
time?  Something like:

diff --git a/block/bio.c b/block/bio.c
index a3893d80dccc9..15da722ed26d1 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1158,6 +1158,37 @@ static void bio_put_pages(struct page **pages, size_t size, size_t off)
 		put_page(pages[i]);
 }
 
+static int bio_iov_add_page(struct bio *bio, struct page *page,
+		unsigned int len, unsigned int offset)
+{
+	bool same_page = false;
+
+	if (!__bio_try_merge_page(bio, page, len, offset, &same_page)) {
+		if (WARN_ON_ONCE(bio_full(bio, len)))
+			return -EINVAL;
+		__bio_add_page(bio, page, len, offset);
+		return 0;
+	}
+
+	if (same_page)
+		put_page(page);
+	return 0;
+}
+
+static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page,
+		unsigned int len, unsigned int offset)
+{
+	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
+	bool same_page = false;
+
+	if (bio_add_hw_page(q, bio, page, len, offset,
+			queue_max_zone_append_sectors(q), &same_page) != len)
+		return -EINVAL;
+	if (same_page)
+		put_page(page);
+	return 0;
+}
+
 #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))
 
 /**
@@ -1176,7 +1207,6 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
 	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
 	struct page **pages = (struct page **)bv;
-	bool same_page = false;
 	ssize_t size, left;
 	unsigned len, i;
 	size_t offset;
@@ -1195,18 +1225,18 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 
 	for (left = size, i = 0; left > 0; left -= len, i++) {
 		struct page *page = pages[i];
+		int ret;
 
 		len = min_t(size_t, PAGE_SIZE - offset, left);
+		if (bio_op(bio) == REQ_OP_ZONE_APPEND)	
+			ret = bio_iov_add_zone_append_page(bio, page, len,
+					offset);
+		else
+			ret = bio_iov_add_page(bio, page, len, offset);
 
-		if (__bio_try_merge_page(bio, page, len, offset, &same_page)) {
-			if (same_page)
-				put_page(page);
-		} else {
-			if (WARN_ON_ONCE(bio_full(bio, len))) {
-				bio_put_pages(pages + i, left, offset);
-				return -EINVAL;
-			}
-			__bio_add_page(bio, page, len, offset);
+		if (ret) {
+			bio_put_pages(pages + i, left, offset);
+			return ret;
 		}
 		offset = 0;
 	}
@@ -1215,54 +1245,6 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	return 0;
 }
 
-static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
-{
-	unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
-	unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
-	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
-	unsigned int max_append_sectors = queue_max_zone_append_sectors(q);
-	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
-	struct page **pages = (struct page **)bv;
-	ssize_t size, left;
-	unsigned len, i;
-	size_t offset;
-	int ret = 0;
-
-	if (WARN_ON_ONCE(!max_append_sectors))
-		return 0;
-
-	/*
-	 * Move page array up in the allocated memory for the bio vecs as far as
-	 * possible so that we can start filling biovecs from the beginning
-	 * without overwriting the temporary page array.
-	 */
-	BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
-	pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
-
-	size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
-	if (unlikely(size <= 0))
-		return size ? size : -EFAULT;
-
-	for (left = size, i = 0; left > 0; left -= len, i++) {
-		struct page *page = pages[i];
-		bool same_page = false;
-
-		len = min_t(size_t, PAGE_SIZE - offset, left);
-		if (bio_add_hw_page(q, bio, page, len, offset,
-				max_append_sectors, &same_page) != len) {
-			bio_put_pages(pages + i, left, offset);
-			ret = -EINVAL;
-			break;
-		}
-		if (same_page)
-			put_page(page);
-		offset = 0;
-	}
-
-	iov_iter_advance(iter, size - left);
-	return ret;
-}
-
 /**
  * bio_iov_iter_get_pages - add user or kernel pages to a bio
  * @bio: bio to add pages to
@@ -1297,10 +1279,7 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	}
 
 	do {
-		if (bio_op(bio) == REQ_OP_ZONE_APPEND)
-			ret = __bio_iov_append_get_pages(bio, iter);
-		else
-			ret = __bio_iov_iter_get_pages(bio, iter);
+		ret = __bio_iov_iter_get_pages(bio, iter);
 	} while (!ret && iov_iter_count(iter) && !bio_full(bio, 0));
 
 	/* don't account direct I/O as memory stall */