Merge patch series "iomap: buffered io changes"

This series contains several fixes and cleanups:

* Renaming bytes_pending/bytes_accounted to
  bytes_submitted/bytes_not_submitted for improved code clarity

* Accounting for unaligned end offsets when truncating read ranges

* Adding documentation for iomap_finish_folio_write() requirements

* Optimizing pending async writeback accounting logic

* Simplifying error handling in ->read_folio_range() for read operations

* Streamlining logic for skipping reads during write operations

* Replacing manual bitmap scanning with find_next_bit() for both dirty
  and uptodate bitmaps, improving performance

* patches from https://patch.msgid.link/20251111193658.3495942-1-joannelkoong@gmail.com:
  iomap: use find_next_bit() for uptodate bitmap scanning
  iomap: use find_next_bit() for dirty bitmap scanning
  iomap: simplify when reads can be skipped for writes
  iomap: simplify ->read_folio_range() error handling for reads
  iomap: optimize pending async writeback accounting
  docs: document iomap writeback's iomap_finish_folio_write() requirement
  iomap: account for unaligned end offsets when truncating read range
  iomap: rename bytes_pending/bytes_accounted to bytes_submitted/bytes_not_submitted

Link: https://patch.msgid.link/20251111193658.3495942-1-joannelkoong@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

Documentation/filesystems/iomap/operations.rst

@@ -149,10 +149,9 @@ These ``struct kiocb`` flags are significant for buffered I/O with iomap:
 iomap calls these functions:
 
   - ``read_folio_range``: Called to read in the range. This must be provided
-    by the caller. The caller is responsible for calling
-    iomap_finish_folio_read() after reading in the folio range. This should be
-    done even if an error is encountered during the read. This returns 0 on
-    success or a negative error on failure.
+    by the caller. If this succeeds, iomap_finish_folio_read() must be called
+    after the range is read in, regardless of whether the read succeeded or
+    failed.
 
   - ``submit_read``: Submit any pending read requests. This function is
     optional.
@@ -361,6 +360,9 @@ The fields are as follows:
     delalloc reservations to avoid having delalloc reservations for
     clean pagecache.
     This function must be supplied by the filesystem.
+    If this succeeds, iomap_finish_folio_write() must be called once writeback
+    completes for the range, regardless of whether the writeback succeeded or
+    failed.
 
   - ``writeback_submit``: Submit the previous built writeback context.
     Block based file systems should use the iomap_ioend_writeback_submit

fs/fuse/file.c

@@ -922,21 +922,15 @@ static int fuse_iomap_read_folio_range_async(const struct iomap_iter *iter,
 
 	if (ctx->rac) {
 		ret = fuse_handle_readahead(folio, ctx->rac, data, pos, len);
-		/*
-		 * If fuse_handle_readahead was successful, fuse_readpages_end
-		 * will do the iomap_finish_folio_read, else we need to call it
-		 * here
-		 */
-		if (ret)
-			iomap_finish_folio_read(folio, off, len, ret);
 	} else {
 		/*
 		 *  for non-readahead read requests, do reads synchronously
 		 *  since it's not guaranteed that the server can handle
 		 *  out-of-order reads
 		 */
 		ret = fuse_do_readfolio(file, folio, off, len);
-		iomap_finish_folio_read(folio, off, len, ret);
+		if (!ret)
+			iomap_finish_folio_read(folio, off, len, ret);
 	}
 	return ret;
 }
@@ -1885,7 +1879,8 @@ static void fuse_writepage_finish(struct fuse_writepage_args *wpa)
 		 * scope of the fi->lock alleviates xarray lock
 		 * contention and noticeably improves performance.
 		 */
-		iomap_finish_folio_write(inode, ap->folios[i], 1);
+		iomap_finish_folio_write(inode, ap->folios[i],
+					 ap->descs[i].length);
 
 	wake_up(&fi->page_waitq);
 }
@@ -2221,7 +2216,6 @@ static ssize_t fuse_iomap_writeback_range(struct iomap_writepage_ctx *wpc,
 		ap = &wpa->ia.ap;
 	}
 
-	iomap_start_folio_write(inode, folio, 1);
 	fuse_writepage_args_page_fill(wpa, folio, ap->num_folios,
 				      offset, len);
 	data->nr_bytes += len;