btrfs: refactor alloc_extent_buffer() to allocate-then-attach method

Currently alloc_extent_buffer() utilizes find_or_create_page() to
allocate one page a time for an extent buffer.

This method has the following disadvantages:

- find_or_create_page() is the legacy way of allocating new pages
  With the new folio infrastructure, find_or_create_page() is just
  redirected to filemap_get_folio().

- Lacks the way to support higher order (order >= 1) folios
  As we can not yet let filemap give us a higher order folio.

This patch would change the workflow by the following way:

		Old		   |		new
-----------------------------------+-------------------------------------
                                   | ret = btrfs_alloc_page_array();
for (i = 0; i < num_pages; i++) {  | for (i = 0; i < num_pages; i++) {
    p = find_or_create_page();     |     ret = filemap_add_folio();
    /* Attach page private */      |     /* Reuse page cache if needed */
    /* Reused eb if needed */      |
				   |     /* Attach page private and
				   |        reuse eb if needed */
				   | }

By this we split the page allocation and private attaching into two
parts, allowing future updates to each part more easily, and migrate to
folio interfaces (especially for possible higher order folios).

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 90f12c0e88a1..792c8e17c31d 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -964,7 +964,7 @@ static int alloc_rbio_pages(struct btrfs_raid_bio *rbio)
 {
 	int ret;
 
-	ret = btrfs_alloc_page_array(rbio->nr_pages, rbio->stripe_pages);
+	ret = btrfs_alloc_page_array(rbio->nr_pages, rbio->stripe_pages, 0);
 	if (ret < 0)
 		return ret;
 	/* Mapping all sectors */
@@ -979,7 +979,7 @@ static int alloc_rbio_parity_pages(struct btrfs_raid_bio *rbio)
 	int ret;
 
 	ret = btrfs_alloc_page_array(rbio->nr_pages - data_pages,
-				     rbio->stripe_pages + data_pages);
+				     rbio->stripe_pages + data_pages, 0);
 	if (ret < 0)
 		return ret;
 
@@ -1530,7 +1530,7 @@ static int alloc_rbio_data_pages(struct btrfs_raid_bio *rbio)
 	const int data_pages = rbio->nr_data * rbio->stripe_npages;
 	int ret;
 
-	ret = btrfs_alloc_page_array(data_pages, rbio->stripe_pages);
+	ret = btrfs_alloc_page_array(data_pages, rbio->stripe_pages, 0);
 	if (ret < 0)
 		return ret;