linux-ext4 - [PATCH] jbd2: improve comments about freeing data buffers whose page mapping is NULL

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Date:   Mon, 17 Feb 2020 19:27:06 +0800
From:   "zhangyi (F)" <yi.zhang@...wei.com>
To:     <linux-ext4@...r.kernel.org>
CC:     <jack@...e.cz>, <tytso@....edu>, <yi.zhang@...wei.com>
Subject: [PATCH] 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.

Fixes: c96dceeabf76 ("jbd2: do not clear the BH_Mapped flag when forgetting a metadata buffer")
Signed-off-by: zhangyi (F) <yi.zhang@...wei.com>
Suggested-by: Jan Kara <jack@...e.cz>
---
 fs/jbd2/commit.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 27373f5792a4..e855d8260433 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -997,9 +997,10 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 			 * 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)) {
-- 
2.17.2