2020-02-17 12:36:45

by Zhang Yi

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) <[email protected]>
Suggested-by: Jan Kara <[email protected]>
---
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

2020-02-17 12:54:55

by Jan Kara

Subject: Re: [PATCH] jbd2: improve comments about freeing data buffers whose page mapping is NULL

On Mon 17-02-20 19:27:06, zhangyi (F) wrote:
> 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) <[email protected]>
> Suggested-by: Jan Kara <[email protected]>

Thanks! You can add:

Reviewed-by: Jan Kara <[email protected]>

Honza

> ---
> 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
>
--
Jan Kara <[email protected]>
SUSE Labs, CR

2020-03-06 01:16:23

by Theodore Ts'o

Subject: Re: [PATCH] jbd2: improve comments about freeing data buffers whose page mapping is NULL

On Mon, Feb 17, 2020 at 07:27:06PM +0800, zhangyi (F) wrote:
> 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) <[email protected]>
> Suggested-by: Jan Kara <[email protected]>

Thanks, applied.

- Ted