btrfs: make nodesize >= PAGE_SIZE case to reuse the non-subpage routine

The reason why we only support 64K page size for subpage is, for 64K
page size we can ensure no matter what the nodesize is, we can fit it
into one page.

When other page size come, especially like 16K, the limitation is a bit
limiting.

To remove such limitation, we allow nodesize >= PAGE_SIZE case to go the
non-subpage routine.  By this, we can allow 4K sectorsize on 16K page
size.

Although this introduces another smaller limitation, the metadata can
not cross page boundary, which is already met by most recent mkfs.

Another small improvement is, we can avoid the overhead for metadata if
nodesize >= PAGE_SIZE.
For 4K sector size and 64K page size/node size, or 4K sector size and
16K page size/node size, we don't need to allocate extra memory for the
metadata pages.

Please note that, this patch will not yet enable other page size support
yet.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index 7accb5c40d33..0e80ad336904 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -74,6 +74,8 @@ enum btrfs_subpage_type {
 	BTRFS_SUBPAGE_DATA,
 };
 
+bool btrfs_is_subpage(const struct btrfs_fs_info *fs_info, struct page *page);
+
 void btrfs_init_subpage_info(struct btrfs_subpage_info *subpage_info, u32 sectorsize);
 int btrfs_attach_subpage(const struct btrfs_fs_info *fs_info,
 			 struct page *page, enum btrfs_subpage_type type);