[PATCH 2/2] ext4: Remove array of buffer_heads from mext_page_mkuptodate()

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

The current code iterates over the list of buffer_heads, finds the
!uptodate ones and reads them, waiting for each one before submitting
the next one.  Instead, submit all the read requests before waiting
for each of the needed ones.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 fs/ext4/move_extent.c | 45 ++++++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 7cd4afa4de1d..529061fa3fbf 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -166,15 +166,16 @@ mext_folio_double_lock(struct inode *inode1, struct inode *inode2,
 	return 0;
 }
 
-/* Force page buffers uptodate w/o dropping page's lock */
-static int
-mext_page_mkuptodate(struct folio *folio, unsigned from, unsigned to)
+/* Force folio buffers uptodate w/o dropping folio's lock */
+static int mext_page_mkuptodate(struct folio *folio, size_t from, size_t to)
 {
 	struct inode *inode = folio->mapping->host;
 	sector_t block;
-	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
+	struct buffer_head *bh, *head;
 	unsigned int blocksize, block_start, block_end;
-	int i, err,  nr = 0, partial = 0;
+	int err = 0,  nr = 0;
+	bool partial = false;
+
 	BUG_ON(!folio_test_locked(folio));
 	BUG_ON(folio_test_writeback(folio));
 
@@ -186,13 +187,14 @@ mext_page_mkuptodate(struct folio *folio, unsigned from, unsigned to)
 	if (!head)
 		head = create_empty_buffers(folio, blocksize, 0);
 
-	block = (sector_t)folio->index << (PAGE_SHIFT - inode->i_blkbits);
-	for (bh = head, block_start = 0; bh != head || !block_start;
-	     block++, block_start = block_end, bh = bh->b_this_page) {
+	block = folio_pos(folio) >> inode->i_blkbits;
+	block_end = 0;
+	for (bh = head; bh != head; block++, bh = bh->b_this_page) {
+		block_start = block_end;
 		block_end = block_start + blocksize;
 		if (block_end <= from || block_start >= to) {
 			if (!buffer_uptodate(bh))
-				partial = 1;
+				partial = true;
 			continue;
 		}
 		if (buffer_uptodate(bh))
@@ -209,25 +211,28 @@ mext_page_mkuptodate(struct folio *folio, unsigned from, unsigned to)
 				continue;
 			}
 		}
-		BUG_ON(nr >= MAX_BUF_PER_PAGE);
-		arr[nr++] = bh;
+		ext4_read_bh_nowait(bh, 0, NULL);
+		nr++;
 	}
 	/* No io required */
 	if (!nr)
 		goto out;
 
-	for (i = 0; i < nr; i++) {
-		bh = arr[i];
-		if (!bh_uptodate_or_lock(bh)) {
-			err = ext4_read_bh(bh, 0, NULL);
-			if (err)
-				return err;
-		}
+	for (bh = head; bh != head; bh = bh->b_this_page) {
+		if (bh_offset(bh) + blocksize <= from)
+			continue;
+		if (bh_offset(bh) > to)
+			break;
+		wait_on_buffer(bh);
+		if (buffer_uptodate(bh))
+			continue;
+		err = -EIO;
+		break;
 	}
 out:
-	if (!partial)
+	if (!err && !partial)
 		folio_mark_uptodate(folio);
-	return 0;
+	return err;
 }
 
 /**
-- 
2.43.0