[PATCH v2 09/24] btrfs: extent_io: calculate inline extent buffer page size based on page size

[Qu Wenruo <wqu@suse.com>]

Btrfs only support 64K as max node size, thus for 4K page system, we
would have at most 16 pages for one extent buffer.

For a system using 64K page size, we would really have just one
single page.

While we always use 16 pages for extent_buffer::pages[], this means for
systems using 64K pages, we are wasting memory for the 15 pages which
will never be utilized.

So this patch will change how the extent_buffer::pages[] array size is
calclulated, now it will be calculated using
BTRFS_MAX_METADATA_BLOCKSIZE and PAGE_SIZE.

For systems using 4K page size, it will stay 16 pages.
For systems using 64K page size, it will be just 1 page.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/extent_io.c | 7 +------
 fs/btrfs/extent_io.h | 8 +++++---
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 37dd103213f9..ca3eb095a298 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5042,12 +5042,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
 	atomic_set(&eb->refs, 1);
 	atomic_set(&eb->io_pages, 0);
 
-	/*
-	 * Sanity checks, currently the maximum is 64k covered by 16x 4k pages
-	 */
-	BUILD_BUG_ON(BTRFS_MAX_METADATA_BLOCKSIZE
-		> MAX_INLINE_EXTENT_BUFFER_SIZE);
-	BUG_ON(len > MAX_INLINE_EXTENT_BUFFER_SIZE);
+	ASSERT(len <= BTRFS_MAX_METADATA_BLOCKSIZE);
 
 	return eb;
 }
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index c76697fc3120..dfdef9c5c379 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -73,9 +73,11 @@ typedef blk_status_t (submit_bio_hook_t)(struct inode *inode, struct bio *bio,
 
 typedef blk_status_t (extent_submit_bio_start_t)(struct inode *inode,
 		struct bio *bio, u64 bio_offset);
-
-#define INLINE_EXTENT_BUFFER_PAGES 16
-#define MAX_INLINE_EXTENT_BUFFER_SIZE (INLINE_EXTENT_BUFFER_PAGES * PAGE_SIZE)
+/*
+ * The SZ_64K is BTRFS_MAX_METADATA_BLOCKSIZE, here just to avoid circle
+ * including "ctree.h".
+ */
+#define INLINE_EXTENT_BUFFER_PAGES (SZ_64K / PAGE_SIZE)
 struct extent_buffer {
 	u64 start;
 	unsigned long len;
-- 
2.29.2