btrfs: merge nr_pages input and output parameter in compress_pages

The parameter saying how many pages can be allocated at maximum can be
merged with the output page counter, to save some stack space.  The
compression implementation will sink the parameter to a local variable
so everything works as before.

The nr_pages variables can also be simply merged in compress_file_range
into one.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -914,8 +914,8 @@ static void free_workspaces(void)
  * Given an address space and start and length, compress the bytes into @pages
  * that are allocated on demand.
  *
- * @out_pages is used to return the number of pages allocated.  There
- * may be pages allocated even if we return an error.
+ * @out_pages is an in/out parameter, holds maximum number of pages to allocate
+ * and returns number of actually allocated pages
  *
  * @total_in is used to return the number of bytes actually read.  It
  * may be smaller than the input length if we had to exit early because we
@@ -930,7 +930,6 @@ static void free_workspaces(void)
  */
 int btrfs_compress_pages(int type, struct address_space *mapping,
 			 u64 start, struct page **pages,
-			 unsigned long nr_dest_pages,
 			 unsigned long *out_pages,
 			 unsigned long *total_in,
 			 unsigned long *total_out,
@@ -943,7 +942,7 @@ int btrfs_compress_pages(int type, struct address_space *mapping,
 
 	ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
 						      start, pages,
-						      nr_dest_pages, out_pages,
+						      out_pages,
 						      total_in, total_out,
 						      max_out);
 	free_workspace(type, workspace);

fs/btrfs/compression.h

@@ -24,7 +24,6 @@ void btrfs_exit_compress(void);
 
 int btrfs_compress_pages(int type, struct address_space *mapping,
 			 u64 start, struct page **pages,
-			 unsigned long nr_dest_pages,
 			 unsigned long *out_pages,
 			 unsigned long *total_in,
 			 unsigned long *total_out,
@@ -60,7 +59,6 @@ struct btrfs_compress_op {
 			      struct address_space *mapping,
 			      u64 start,
 			      struct page **pages,
-			      unsigned long nr_dest_pages,
 			      unsigned long *out_pages,
 			      unsigned long *total_in,
 			      unsigned long *total_out,

fs/btrfs/inode.c

@@ -430,7 +430,6 @@ static noinline void compress_file_range(struct inode *inode,
 	int ret = 0;
 	struct page **pages = NULL;
 	unsigned long nr_pages;
-	unsigned long nr_pages_ret = 0;
 	unsigned long total_compressed = 0;
 	unsigned long total_in = 0;
 	unsigned long max_compressed = SZ_128K;
@@ -518,7 +517,7 @@ static noinline void compress_file_range(struct inode *inode,
 		ret = btrfs_compress_pages(compress_type,
 					   inode->i_mapping, start,
 					   pages,
-					   nr_pages, &nr_pages_ret,
+					   &nr_pages,
 					   &total_in,
 					   &total_compressed,
 					   max_compressed);
@@ -526,7 +525,7 @@ static noinline void compress_file_range(struct inode *inode,
 		if (!ret) {
 			unsigned long offset = total_compressed &
 				(PAGE_SIZE - 1);
-			struct page *page = pages[nr_pages_ret - 1];
+			struct page *page = pages[nr_pages - 1];
 			char *kaddr;
 
 			/* zero the tail end of the last page, we might be
@@ -607,7 +606,7 @@ static noinline void compress_file_range(struct inode *inode,
 			 * will submit them to the elevator.
 			 */
 			add_async_extent(async_cow, start, num_bytes,
-					total_compressed, pages, nr_pages_ret,
+					total_compressed, pages, nr_pages,
 					compress_type);
 
 			if (start + num_bytes < end) {
@@ -624,14 +623,14 @@ static noinline void compress_file_range(struct inode *inode,
 		 * the compression code ran but failed to make things smaller,
 		 * free any pages it allocated and our page pointer array
 		 */
-		for (i = 0; i < nr_pages_ret; i++) {
+		for (i = 0; i < nr_pages; i++) {
 			WARN_ON(pages[i]->mapping);
 			put_page(pages[i]);
 		}
 		kfree(pages);
 		pages = NULL;
 		total_compressed = 0;
-		nr_pages_ret = 0;
+		nr_pages = 0;
 
 		/* flag the file so we don't compress in the future */
 		if (!btrfs_test_opt(fs_info, FORCE_COMPRESS) &&
@@ -660,7 +659,7 @@ static noinline void compress_file_range(struct inode *inode,
 	return;
 
 free_pages_out:
-	for (i = 0; i < nr_pages_ret; i++) {
+	for (i = 0; i < nr_pages; i++) {
 		WARN_ON(pages[i]->mapping);
 		put_page(pages[i]);
 	}

fs/btrfs/lzo.c

@@ -88,7 +88,6 @@ static int lzo_compress_pages(struct list_head *ws,
 			      struct address_space *mapping,
 			      u64 start,
 			      struct page **pages,
-			      unsigned long nr_dest_pages,
 			      unsigned long *out_pages,
 			      unsigned long *total_in,
 			      unsigned long *total_out,
@@ -103,6 +102,7 @@ static int lzo_compress_pages(struct list_head *ws,
 	struct page *out_page = NULL;
 	unsigned long bytes_left;
 	unsigned long len = *total_out;
+	unsigned long nr_dest_pages = *out_pages;
 	size_t in_len;
 	size_t out_len;
 	char *buf;

fs/btrfs/zlib.c

@@ -75,7 +75,6 @@ static int zlib_compress_pages(struct list_head *ws,
 			       struct address_space *mapping,
 			       u64 start,
 			       struct page **pages,
-			       unsigned long nr_dest_pages,
 			       unsigned long *out_pages,
 			       unsigned long *total_in,
 			       unsigned long *total_out,
@@ -90,6 +89,7 @@ static int zlib_compress_pages(struct list_head *ws,
 	struct page *out_page = NULL;
 	unsigned long bytes_left;
 	unsigned long len = *total_out;
+	unsigned long nr_dest_pages = *out_pages;
 
 	*out_pages = 0;
 	*total_out = 0;