[PATCH 06/10] mm,btrfs: add a filemap_flush_nr helper

[Christoph Hellwig <hch@lst.de>]

Abstract out the btrfs-specific behavior of kicking off I/O on a number
of pages on an address_space into a well-defined helper.

Note: there is no kerneldoc comment for the new function because it is
not part of the public API.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/inode.c        | 13 ++-----------
 include/linux/pagemap.h |  1 +
 mm/filemap.c            | 22 ++++++++++++++++++++++
 3 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b97d6c1f7772..d12b8116adde 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8752,19 +8752,10 @@ static int start_delalloc_inodes(struct btrfs_root *root, long *nr_to_write,
 			btrfs_queue_work(root->fs_info->flush_workers,
 					 &work->work);
 		} else {
-			struct writeback_control wbc = {
-				.nr_to_write = *nr_to_write,
-				.sync_mode = WB_SYNC_NONE,
-				.range_start = 0,
-				.range_end = LLONG_MAX,
-			};
-
-			ret = filemap_fdatawrite_wbc(tmp_inode->i_mapping,
-					&wbc);
+			ret = filemap_flush_nr(tmp_inode->i_mapping,
+					nr_to_write);
 			btrfs_add_delayed_iput(inode);
 
-			if (*nr_to_write != LONG_MAX)
-				*nr_to_write = wbc.nr_to_write;
 			if (ret || *nr_to_write <= 0)
 				goto out;
 		}
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 09b581c1d878..cebdf160d3dd 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -38,6 +38,7 @@ int filemap_invalidate_pages(struct address_space *mapping,
 int write_inode_now(struct inode *, int sync);
 int filemap_fdatawrite(struct address_space *);
 int filemap_flush(struct address_space *);
+int filemap_flush_nr(struct address_space *mapping, long *nr_to_write);
 int filemap_fdatawait_keep_errors(struct address_space *mapping);
 int filemap_fdatawait_range(struct address_space *, loff_t lstart, loff_t lend);
 int filemap_fdatawait_range_keep_errors(struct address_space *mapping,
diff --git a/mm/filemap.c b/mm/filemap.c
index 99d6919af60d..e344b79a012d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -474,6 +474,28 @@ int filemap_flush(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_flush);
 
+/*
+ * Start writeback on @nr_to_write pages from @mapping.  No one but the existing
+ * btrfs caller should be using this.  Talk to linux-mm if you think adding a
+ * new caller is a good idea.
+ */
+int filemap_flush_nr(struct address_space *mapping, long *nr_to_write)
+{
+	struct writeback_control wbc = {
+		.nr_to_write = *nr_to_write,
+		.sync_mode = WB_SYNC_NONE,
+		.range_start = 0,
+		.range_end = LLONG_MAX,
+	};
+	int ret;
+
+	ret = filemap_fdatawrite_wbc(mapping, &wbc);
+	if (!ret)
+		*nr_to_write = wbc.nr_to_write;
+	return ret;
+}
+EXPORT_SYMBOL_FOR_MODULES(filemap_flush_nr, "btrfs");
+
 /**
  * filemap_range_has_page - check if a page exists in range.
  * @mapping:           address space within which to check
-- 
2.47.3