fuse：未缓存 readdir 缓冲区用页支撑 — 减少目录遍历内存拷贝

+static struct page **fuse_readdir_alloc_buf(struct fuse_args_pages *ap, size_t *bufsize)
+{
+	unsigned int i, nr_alloc, nr_pages = DIV_ROUND_UP(*bufsize, PAGE_SIZE);
+	struct page **pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL);
+
+	if (!pages)
+		return NULL;
+
+	nr_alloc = alloc_pages_bulk(GFP_KERNEL, nr_pages, pages);
+	if (!nr_alloc)
+		goto free_array;
+
+	if (nr_alloc < nr_pages) {
+		nr_pages = nr_alloc;
+		*bufsize = (size_t) nr_pages << PAGE_SHIFT;
+	}
+
+	ap->folios = fuse_folios_alloc(nr_pages, GFP_KERNEL, &ap->descs);
+	if (!ap->folios)
+		goto release_pages;
+
+	for (i = 0; i < nr_pages; i++) {
+		ap->folios[i] = page_folio(pages[i]);
+		ap->descs[i].length = min_t(size_t, *bufsize - (size_t)i * PAGE_SIZE, PAGE_SIZE);
+	}
+	ap->num_folios = nr_pages;
+	ap->args.out_pages = true;
+
+	return pages;
+...

-	buf = kvmalloc(bufsize, GFP_KERNEL);
-	if (!buf)
+	struct page **pages = fuse_readdir_alloc_buf(ap, &bufsize);
+
+	if (!pages)
 		return -ENOMEM;
 
-	args->out_args[0].value = buf;
-
 	plus = fuse_use_readdirplus(inode, ctx);
 	...
-	res = fuse_simple_request(fm, args);
+	res = fuse_simple_request(fm, &ap->args);
 	fuse_unlock_inode(inode, locked);
-	if (res >= 0) {
-		...
-	} else if (plus) {
-		res = parse_dirplusfile(buf, res, file, ctx, attr_version, evict_ctr);
-	} else {
+	...
+	buf = vm_map_ram(pages, ap->num_folios, -1);
+	if (!buf) {
+		res = -ENOMEM;
+	} else {
+		if (plus)
+			res = parse_dirplusfile(buf, res, file, ctx, attr_version, evict_ctr);
+		else
+			res = parse_dirfile(buf, res, file, ctx);
+
+		vm_unmap_ram(buf, ap->num_folios);
 	}
+out:
+	kfree(ap->folios);
+	release_pages(pages, ap->num_folios);
+	kfree(pages);
 
-	kvfree(buf);
 	fuse_invalidate_atime(inode);