btrfs: don't redirty pages in compress_file_range

compress_file_range needs to clear the dirty bit before handing off work
to the compression worker threads to prevent processes coming in through
mmap and changing the file contents while the compression is accessing
the data (See commit 4adaa611020f ("Btrfs: fix race between mmap writes
and compression").

But when compress_file_range decides to not compress the data, it falls
back to submit_uncompressed_range which uses extent_write_locked_range
to write the uncompressed data.  extent_write_locked_range currently
expects all pages to be marked dirty so that it can clear the dirty
bit itself, and thus compress_file_range has to redirty the page range.

Redirtying the page range is rather inefficient and also pointless,
so instead pass a pages_dirty parameter to extent_write_locked_range
and skip the redirty game entirely.

Note that compress_file_range was even redirtying the locked_page twice
given that extent_range_clear_dirty_for_io already redirties all pages
in the range, which must include locked_page if there is one.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 0312022bbf4b..2678906e87c5 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -178,7 +178,7 @@ int try_release_extent_buffer(struct page *page);
 
 int btrfs_read_folio(struct file *file, struct folio *folio);
 void extent_write_locked_range(struct inode *inode, u64 start, u64 end,
-			       struct writeback_control *wbc);
+			       struct writeback_control *wbc, bool pages_dirty);
 int extent_writepages(struct address_space *mapping,
 		      struct writeback_control *wbc);
 int btree_write_cache_pages(struct address_space *mapping,
@@ -265,7 +265,6 @@ void set_extent_buffer_dirty(struct extent_buffer *eb);
 void set_extent_buffer_uptodate(struct extent_buffer *eb);
 void clear_extent_buffer_uptodate(struct extent_buffer *eb);
 void extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end);
-void extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end);
 void extent_clear_unlock_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
 				  struct page *locked_page,
 				  u32 bits_to_clear, unsigned long page_ops);