jbd2: improve comments about freeing data buffers whose page mapping is NULL

Improve comments in jbd2_journal_commit_transaction() to describe why
we don't need to clear the buffer_mapped bit for freeing file mapping
buffers whose page mapping is NULL.

Link: https://lore.kernel.org/r/20200217112706.20085-1-yi.zhang@huawei.com
Fixes: c96dceeabf76 ("jbd2: do not clear the BH_Mapped flag when forgetting a metadata buffer")
Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 27373f5792a4f7a5a846742cb44e624ad56f5377..e855d8260433a2c890f0cc30b10980717c1c2858 100644 (file)
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -997,9 +997,10 @@ restart_loop:
                         * journalled data) we need to unmap buffer and clear
                         * more bits. We also need to be careful about the check
                         * because the data page mapping can get cleared under
-                        * out hands, which alse need not to clear more bits
-                        * because the page and buffers will be freed and can
-                        * never be reused once we are done with them.
+                        * our hands. Note that if mapping == NULL, we don't
+                        * need to make buffer unmapped because the page is
+                        * already detached from the mapping and buffers cannot
+                        * get reused.
                         */
                        mapping = READ_ONCE(bh->b_page->mapping);
                        if (mapping && !sb_is_blkdev_sb(mapping->host->i_sb)) {