btrfs: factor out allocating an array of pages

Several functions currently populate an array of page pointers one
allocated page at a time. Factor out the common code so as to allow
improvements to all of the sites at once.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/check-integrity.c

@@ -1552,11 +1552,9 @@ static int btrfsic_read_block(struct btrfsic_state *state,
 		return -ENOMEM;
 	block_ctx->datav = block_ctx->mem_to_free;
 	block_ctx->pagev = (struct page **)(block_ctx->datav + num_pages);
-	for (i = 0; i < num_pages; i++) {
-		block_ctx->pagev[i] = alloc_page(GFP_NOFS);
-		if (!block_ctx->pagev[i])
-			return -1;
-	}
+	ret = btrfs_alloc_page_array(num_pages, block_ctx->pagev);
+	if (ret)
+		return ret;
 
 	dev_bytenr = block_ctx->dev_bytenr;
 	for (i = 0; i < num_pages;) {

fs/btrfs/compression.c

@@ -809,8 +809,6 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	struct extent_map_tree *em_tree;
 	struct compressed_bio *cb;
 	unsigned int compressed_len;
-	unsigned int nr_pages;
-	unsigned int pg_index;
 	struct bio *comp_bio = NULL;
 	const u64 disk_bytenr = bio->bi_iter.bi_sector << SECTOR_SHIFT;
 	u64 cur_disk_byte = disk_bytenr;
@@ -820,7 +818,8 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	u64 em_start;
 	struct extent_map *em;
 	blk_status_t ret;
-	int faili = 0;
+	int ret2;
+	int i;
 	u8 *sums;
 
 	em_tree = &BTRFS_I(inode)->extent_tree;
@@ -863,24 +862,18 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	cb->compress_type = extent_compress_type(bio_flags);
 	cb->orig_bio = bio;
 
-	nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE);
-	cb->compressed_pages = kcalloc(nr_pages, sizeof(struct page *),
-				       GFP_NOFS);
+	cb->nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE);
+	cb->compressed_pages = kcalloc(cb->nr_pages, sizeof(struct page *), GFP_NOFS);
 	if (!cb->compressed_pages) {
 		ret = BLK_STS_RESOURCE;
-		goto fail1;
+		goto fail;
 	}
 
-	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
-		cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS);
-		if (!cb->compressed_pages[pg_index]) {
-			faili = pg_index - 1;
-			ret = BLK_STS_RESOURCE;
-			goto fail2;
-		}
+	ret2 = btrfs_alloc_page_array(cb->nr_pages, cb->compressed_pages);
+	if (ret2) {
+		ret = BLK_STS_RESOURCE;
+		goto fail;
 	}
-	faili = nr_pages - 1;
-	cb->nr_pages = nr_pages;
 
 	add_ra_bio_pages(inode, em_start + em_len, cb);
 
@@ -957,14 +950,15 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	}
 	return BLK_STS_OK;
 
-fail2:
-	while (faili >= 0) {
-		__free_page(cb->compressed_pages[faili]);
-		faili--;
+fail:
+	if (cb->compressed_pages) {
+		for (i = 0; i < cb->nr_pages; i++) {
+			if (cb->compressed_pages[i])
+				__free_page(cb->compressed_pages[i]);
+		}
 	}
 
 	kfree(cb->compressed_pages);
-fail1:
 	kfree(cb);
 out:
 	free_extent_map(em);

fs/btrfs/extent_io.c

@@ -3133,6 +3133,34 @@ static void end_bio_extent_readpage(struct bio *bio)
 	bio_put(bio);
 }
 
+/**
+ * Populate every free slot in a provided array with pages.
+ *
+ * @nr_pages:   number of pages to allocate
+ * @page_array: the array to fill with pages; any existing non-null entries in
+ * 		the array will be skipped
+ *
+ * Return: 0        if all pages were able to be allocated;
+ *         -ENOMEM  otherwise, and the caller is responsible for freeing all
+ *                  non-null page pointers in the array.
+ */
+int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array)
+{
+	int i;
+
+	for (i = 0; i < nr_pages; i++) {
+		struct page *page;
+
+		if (page_array[i])
+			continue;
+		page = alloc_page(GFP_NOFS);
+		if (!page)
+			return -ENOMEM;
+		page_array[i] = page;
+	}
+	return 0;
+}
+
 /*
  * Initialize the members up to but not including 'bio'. Use after allocating a
  * new bio by bio_alloc_bioset as it does not initialize the bytes outside of
@@ -5912,9 +5940,9 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
 struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src)
 {
 	int i;
-	struct page *p;
 	struct extent_buffer *new;
 	int num_pages = num_extent_pages(src);
+	int ret;
 
 	new = __alloc_extent_buffer(src->fs_info, src->start, src->len);
 	if (new == NULL)
@@ -5927,22 +5955,23 @@ struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src)
 	 */
 	set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags);
 
+	memset(new->pages, 0, sizeof(*new->pages) * num_pages);
+	ret = btrfs_alloc_page_array(num_pages, new->pages);
+	if (ret) {
+		btrfs_release_extent_buffer(new);
+		return NULL;
+	}
+
 	for (i = 0; i < num_pages; i++) {
 		int ret;
+		struct page *p = new->pages[i];
 
-		p = alloc_page(GFP_NOFS);
-		if (!p) {
-			btrfs_release_extent_buffer(new);
-			return NULL;
-		}
 		ret = attach_extent_buffer_page(new, p, NULL);
 		if (ret < 0) {
-			put_page(p);
 			btrfs_release_extent_buffer(new);
 			return NULL;
 		}
 		WARN_ON(PageDirty(p));
-		new->pages[i] = p;
 		copy_page(page_address(p), page_address(src->pages[i]));
 	}
 	set_extent_buffer_uptodate(new);
@@ -5956,31 +5985,36 @@ struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
 	struct extent_buffer *eb;
 	int num_pages;
 	int i;
+	int ret;
 
 	eb = __alloc_extent_buffer(fs_info, start, len);
 	if (!eb)
 		return NULL;
 
 	num_pages = num_extent_pages(eb);
+	ret = btrfs_alloc_page_array(num_pages, eb->pages);
+	if (ret)
+		goto err;
+
 	for (i = 0; i < num_pages; i++) {
-		int ret;
+		struct page *p = eb->pages[i];
 
-		eb->pages[i] = alloc_page(GFP_NOFS);
-		if (!eb->pages[i])
-			goto err;
-		ret = attach_extent_buffer_page(eb, eb->pages[i], NULL);
+		ret = attach_extent_buffer_page(eb, p, NULL);
 		if (ret < 0)
 			goto err;
 	}
+
 	set_extent_buffer_uptodate(eb);
 	btrfs_set_header_nritems(eb, 0);
 	set_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
 
 	return eb;
 err:
-	for (; i > 0; i--) {
-		detach_extent_buffer_page(eb, eb->pages[i - 1]);
-		__free_page(eb->pages[i - 1]);
+	for (i = 0; i < num_pages; i++) {
+		if (eb->pages[i]) {
+			detach_extent_buffer_page(eb, eb->pages[i]);
+			__free_page(eb->pages[i]);
+		}
 	}
 	__free_extent_buffer(eb);
 	return NULL;

fs/btrfs/extent_io.h

@@ -277,6 +277,8 @@ void extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end);
 void extent_clear_unlock_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
 				  struct page *locked_page,
 				  u32 bits_to_clear, unsigned long page_ops);
+
+int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array);
 struct bio *btrfs_bio_alloc(unsigned int nr_iovecs);
 struct bio *btrfs_bio_clone(struct bio *bio);
 struct bio *btrfs_bio_clone_partial(struct bio *orig, u64 offset, u64 size);

fs/btrfs/inode.c

@@ -10461,13 +10461,11 @@ static ssize_t btrfs_encoded_read_regular(struct kiocb *iocb,
 	pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
 	if (!pages)
 		return -ENOMEM;
-	for (i = 0; i < nr_pages; i++) {
-		pages[i] = alloc_page(GFP_NOFS);
-		if (!pages[i]) {
-			ret = -ENOMEM;
-			goto out;
+	ret = btrfs_alloc_page_array(nr_pages, pages);
+	if (ret) {
+		ret = -ENOMEM;
+		goto out;
 		}
-	}
 
 	ret = btrfs_encoded_read_regular_fill_pages(inode, start, disk_bytenr,
 						    disk_io_size, pages);

fs/btrfs/raid56.c

@@ -1026,37 +1026,16 @@ static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
 /* allocate pages for all the stripes in the bio, including parity */
 static int alloc_rbio_pages(struct btrfs_raid_bio *rbio)
 {
-	int i;
-	struct page *page;
-
-	for (i = 0; i < rbio->nr_pages; i++) {
-		if (rbio->stripe_pages[i])
-			continue;
-		page = alloc_page(GFP_NOFS);
-		if (!page)
-			return -ENOMEM;
-		rbio->stripe_pages[i] = page;
-	}
-	return 0;
+	return btrfs_alloc_page_array(rbio->nr_pages, rbio->stripe_pages);
 }
 
 /* only allocate pages for p/q stripes */
 static int alloc_rbio_parity_pages(struct btrfs_raid_bio *rbio)
 {
-	int i;
-	struct page *page;
-
-	i = rbio_stripe_page_index(rbio, rbio->nr_data, 0);
+	int data_pages = rbio_stripe_page_index(rbio, rbio->nr_data, 0);
 
-	for (; i < rbio->nr_pages; i++) {
-		if (rbio->stripe_pages[i])
-			continue;
-		page = alloc_page(GFP_NOFS);
-		if (!page)
-			return -ENOMEM;
-		rbio->stripe_pages[i] = page;
-	}
-	return 0;
+	return btrfs_alloc_page_array(rbio->nr_pages - data_pages,
+				      rbio->stripe_pages + data_pages);
 }
 
 /*