[PATCH 2/2] btrfs: utilize cached extent map for data writeback

[Qu Wenruo <wqu@suse.com>]

Unlike data read, we never really utilize the cached extent_map for data
write.

This means we will do the costly extent map lookup for each sector we
need to write back.

Change it to utilize the same function, __get_extent_map(), just like
the data read path, to reduce the overhead of extent map lookup.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d4ad98488c03..9492cd9d4f04 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1357,7 +1357,8 @@ static int submit_one_sector(struct btrfs_inode *inode,
 	/* @filepos >= i_size case should be handled by the caller. */
 	ASSERT(filepos < i_size);
 
-	em = btrfs_get_extent(inode, NULL, filepos, sectorsize);
+	em = __get_extent_map(&inode->vfs_inode, NULL, filepos, sectorsize,
+			      &bio_ctrl->em_cached);
 	if (IS_ERR(em))
 		return PTR_ERR_OR_ZERO(em);
 
@@ -2320,6 +2321,7 @@ void extent_write_locked_range(struct inode *inode, const struct folio *locked_f
 		cur = cur_end + 1;
 	}
 
+	free_extent_map(bio_ctrl.em_cached);
 	submit_write_bio(&bio_ctrl, found_error ? ret : 0);
 }
 
@@ -2338,6 +2340,7 @@ int btrfs_writepages(struct address_space *mapping, struct writeback_control *wb
 	 */
 	btrfs_zoned_data_reloc_lock(BTRFS_I(inode));
 	ret = extent_write_cache_pages(mapping, &bio_ctrl);
+	free_extent_map(bio_ctrl.em_cached);
 	submit_write_bio(&bio_ctrl, ret);
 	btrfs_zoned_data_reloc_unlock(BTRFS_I(inode));
 	return ret;
-- 
2.45.2