btrfs: update num_extent_pages to support subpage sized extent buffer

For subpage sized extent buffer, we have ensured no extent buffer will
cross page boundary, thus we would only need one page for any extent
buffer.

Update function num_extent_pages to handle such case.  Now
num_extent_pages() returns 1 for subpage sized extent buffer.

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

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 77f2211550e3b7136768c739795a8cf021e700dc..19221095c63588c2c20a4620ea57a12b23a2179b 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -203,8 +203,14 @@ void btrfs_readahead_node_child(struct extent_buffer *node, int slot);
 
 static inline int num_extent_pages(const struct extent_buffer *eb)
 {
-       return (round_up(eb->start + eb->len, PAGE_SIZE) >> PAGE_SHIFT) -
-              (eb->start >> PAGE_SHIFT);
+       /*
+        * For sectorsize == PAGE_SIZE case, since nodesize is always aligned to
+        * sectorsize, it's just eb->len >> PAGE_SHIFT.
+        *
+        * For sectorsize < PAGE_SIZE case, we could have nodesize < PAGE_SIZE,
+        * thus have to ensure we get at least one page.
+        */
+       return (eb->len >> PAGE_SHIFT) ?: 1;
 }
 
 static inline int extent_buffer_uptodate(const struct extent_buffer *eb)