[PATCH v2 11/12] iomap: refactor uptodate bitmap iteration

[Joanne Koong <joannelkoong@xxxxxxxxx>]

Use find_next_bit()/find_next_zero_bit() for iomap uptodate bitmap
iteration. This uses __ffs() internally and is more efficient for
finding the next uptodate or non-uptodate bit than manually iterating
through the bitmap range testing every bit.

Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
---
 fs/iomap/buffered-io.c | 74 +++++++++++++++++++++++++++---------------
 1 file changed, 48 insertions(+), 26 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index dc1a1f371412..4f021dcaaffe 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -37,10 +37,36 @@ static inline bool ifs_is_fully_uptodate(struct folio *folio,
 	return bitmap_full(ifs->state, i_blocks_per_folio(inode, folio));
 }
 
-static inline bool ifs_block_is_uptodate(struct iomap_folio_state *ifs,
-		unsigned int block)
+/**
+ * ifs_next_uptodate_block - find the next uptodate block in the folio
+ * @folio: The folio
+ * @start_blk: Block number to begin searching at
+ * @end_blk: Last block number (inclusive) to search
+ *
+ * If no uptodate block is found, this will return end_blk + 1.
+ */
+static unsigned ifs_next_uptodate_block(struct folio *folio,
+		unsigned start_blk, unsigned end_blk)
 {
-	return test_bit(block, ifs->state);
+	struct iomap_folio_state *ifs = folio->private;
+
+	return find_next_bit(ifs->state, end_blk + 1, start_blk);
+}
+
+/**
+ * ifs_next_nonuptodate_block - find the next non-uptodate block in the folio
+ * @folio: The folio
+ * @start_blk: Block number to begin searching at
+ * @end_blk: Last block number (inclusive) to search
+ *
+ * If no non-uptodate block is found, this will return end_blk + 1.
+ */
+static unsigned ifs_next_nonuptodate_block(struct folio *folio,
+		unsigned start_blk, unsigned end_blk)
+{
+	struct iomap_folio_state *ifs = folio->private;
+
+	return find_next_zero_bit(ifs->state, end_blk + 1, start_blk);
 }
 
 static bool ifs_set_range_uptodate(struct folio *folio,
@@ -266,24 +292,23 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
 	 * to avoid reading in already uptodate ranges.
 	 */
 	if (ifs) {
-		unsigned int i;
-
-		/* move forward for each leading block marked uptodate */
-		for (i = first; i <= last; i++) {
-			if (!ifs_block_is_uptodate(ifs, i))
-				break;
-			*pos += block_size;
-			poff += block_size;
-			plen -= block_size;
-			first++;
-		}
-
-		/* truncate len if we find any trailing uptodate block(s) */
-		while (++i <= last) {
-			if (ifs_block_is_uptodate(ifs, i)) {
-				plen -= (last - i + 1) * block_size;
-				last = i - 1;
-				break;
+		unsigned next, bytes;
+
+		/* find the next non-uptodate block */
+		next = ifs_next_nonuptodate_block(folio, first, last);
+		bytes = (next - first) << block_bits;
+		*pos += bytes;
+		poff += bytes;
+		WARN_ON_ONCE(bytes > plen);
+		plen -= bytes;
+		first = next;
+
+		if (++next <= last) {
+			/* truncate len if we find any trailing uptodate block(s) */
+			next = ifs_next_uptodate_block(folio, next, last);
+			if (next <= last) {
+				plen -= (last - next + 1) << block_bits;
+				last = next - 1;
 			}
 		}
 	}
@@ -607,7 +632,7 @@ bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
 {
 	struct iomap_folio_state *ifs = folio->private;
 	struct inode *inode = folio->mapping->host;
-	unsigned first, last, i;
+	unsigned first, last;
 
 	if (!ifs)
 		return false;
@@ -619,10 +644,7 @@ bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
 	first = from >> inode->i_blkbits;
 	last = (from + count - 1) >> inode->i_blkbits;
 
-	for (i = first; i <= last; i++)
-		if (!ifs_block_is_uptodate(ifs, i))
-			return false;
-	return true;
+	return ifs_next_nonuptodate_block(folio, first, last) > last;
 }
 EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);
 
-- 
2.47.3