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[v3,28/49] btrfs: extent_io: update num_extent_pages() to support subpage sized extent buffer

Message ID 20200930015539.48867-29-wqu@suse.com
State New, archived
Headers show
Series btrfs: add partial rw support for subpage sector size | expand

Commit Message

Qu Wenruo Sept. 30, 2020, 1:55 a.m. UTC
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.

This patch will update the function num_extent_pages() to handle such
case.
Now num_extent_pages() would return 1 instead of for subpage sized
extent buffer.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
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Patch

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index e588b3100ede..552afc1c0bbc 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -229,8 +229,15 @@  void wait_on_extent_buffer_writeback(struct extent_buffer *eb);
 
 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 eb is always aligned to
+	 * sectorsize, it's just (eb->len / PAGE_SIZE) >> PAGE_SHIFT.
+	 *
+	 * For sectorsize < PAGE_SIZE case, we only want to support 64K
+	 * PAGE_SIZE, and ensured all tree blocks won't cross page boundary.
+	 * So in that case we always got 1 page.
+	 */
+	return (round_up(eb->len, PAGE_SIZE) >> PAGE_SHIFT);
 }
 
 static inline int extent_buffer_uptodate(const struct extent_buffer *eb)