fuse: support large folios for readahead

Add support for folios larger than one page size for readahead.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: joannekoong

fs/fuse/file.c

@@ -876,14 +876,13 @@ static void fuse_readpages_end(struct fuse_mount *fm, struct fuse_args *args,
 	fuse_io_free(ia);
 }
 
-static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file)
+static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
+				unsigned int count)
 {
 	struct fuse_file *ff = file->private_data;
 	struct fuse_mount *fm = ff->fm;
 	struct fuse_args_pages *ap = &ia->ap;
 	loff_t pos = folio_pos(ap->folios[0]);
-	/* Currently, all folios in FUSE are one page */
-	size_t count = ap->num_folios << PAGE_SHIFT;
 	ssize_t res;
 	int err;
 
@@ -918,6 +917,7 @@ static void fuse_readahead(struct readahead_control *rac)
 	struct inode *inode = rac->mapping->host;
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	unsigned int max_pages, nr_pages;
+	struct folio *folio = NULL;
 
 	if (fuse_is_bad(inode))
 		return;
@@ -939,8 +939,8 @@ static void fuse_readahead(struct readahead_control *rac)
 	while (nr_pages) {
 		struct fuse_io_args *ia;
 		struct fuse_args_pages *ap;
-		struct folio *folio;
 		unsigned cur_pages = min(max_pages, nr_pages);
+		unsigned int pages = 0;
 
 		if (fc->num_background >= fc->congestion_threshold &&
 		    rac->ra->async_size >= readahead_count(rac))
@@ -952,24 +952,44 @@ static void fuse_readahead(struct readahead_control *rac)
 
 		ia = fuse_io_alloc(NULL, cur_pages);
 		if (!ia)
-			return;
+			break;
 		ap = &ia->ap;
 
-		while (ap->num_folios < cur_pages) {
+		while (pages < cur_pages) {
+			unsigned int folio_pages;
+
 			/*
 			 * This returns a folio with a ref held on it.
 			 * The ref needs to be held until the request is
 			 * completed, since the splice case (see
 			 * fuse_try_move_page()) drops the ref after it's
 			 * replaced in the page cache.
 			 */
-			folio = __readahead_folio(rac);
+			if (!folio)
+				folio =  __readahead_folio(rac);
+
+			folio_pages = folio_nr_pages(folio);
+			if (folio_pages > cur_pages - pages) {
+				/*
+				 * Large folios belonging to fuse will never
+				 * have more pages than max_pages.
+				 */
+				WARN_ON(!pages);
+				break;
+			}
+
 			ap->folios[ap->num_folios] = folio;
 			ap->descs[ap->num_folios].length = folio_size(folio);
 			ap->num_folios++;
+			pages += folio_pages;
+			folio = NULL;
 		}
-		fuse_send_readpages(ia, rac->file);
-		nr_pages -= cur_pages;
+		fuse_send_readpages(ia, rac->file, pages << PAGE_SHIFT);
+		nr_pages -= pages;
+	}
+	if (folio) {
+		folio_end_read(folio, false);
+		folio_put(folio);
 	}
 }