linux-ext4 - Re: [PATCH 2/9] jbd2: remove unused return info from jbd2_journal_write_metadata

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Date: Sun, 12 May 2024 12:14:14 +0200
From: Jan Kara <jack@...e.cz>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: Zhang Yi <yi.zhang@...weicloud.com>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, tytso@....edu, jack@...e.com
Subject: Re: [PATCH 2/9] jbd2: remove unused return info from
 jbd2_journal_write_metadata_buffer

On Wed 08-05-24 09:42:30, Kemeng Shi wrote:
> 
> 
> on 5/7/2024 7:51 PM, Zhang Yi wrote:
> > On 2024/5/6 22:17, Kemeng Shi wrote:
> >> The done_copy_out info from jbd2_journal_write_metadata_buffer is not
> >> used. Simply remove it.
> >>
> >> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
> >> ---
> >>  fs/jbd2/journal.c | 3 +--
> >>  1 file changed, 1 insertion(+), 2 deletions(-)
> >>
> >> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> >> index 207b24e12ce9..068031f35aea 100644
> >> --- a/fs/jbd2/journal.c
> >> +++ b/fs/jbd2/journal.c
> >> @@ -320,7 +320,6 @@ static void journal_kill_thread(journal_t *journal)
> >>   *
> >>   * On success:
> >>   * Bit 0 set == escape performed on the data
> >> - * Bit 1 set == buffer copy-out performed (kfree the data after IO)
> >>   */
> >>  
> >>  int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
> >> @@ -455,7 +454,7 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
> >>  	set_buffer_shadow(bh_in);
> >>  	spin_unlock(&jh_in->b_state_lock);
> >>  
> >> -	return do_escape | (done_copy_out << 1);
> >> +	return do_escape;
> >>  }
> >>  
> > 
> > I checked the history, it seems that this bit has not been used since
> > the very beginning when the jbd code was merged in, I suppose we could
> > drop it. Since there is only one flag that is still in use, why not just
> > drop the flag and pass out do_escape through an output parameter, or
> > directly pass tag_flag, after that we could also drop the weird
> > "if (flags & 1)" check in jbd2_journal_commit_transaction()?
> Thanks for looking into this. I agree that the "flags & 1" is wired, I
> wonder if we could further remove "flags & 1" with following change:
> 
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index 5e122586e06e..67077308b56b 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -353,7 +353,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
>         struct buffer_head *descriptor;
>         struct buffer_head **wbuf = journal->j_wbuf;
>         int bufs;
> -       int flags;
> +       int escape;
>         int err;
>         unsigned long long blocknr;
>         ktime_t start_time;
> @@ -661,10 +661,10 @@ void jbd2_journal_commit_transaction(journal_t *journal)
>                  */
>                 set_bit(BH_JWrite, &jh2bh(jh)->b_state);
>                 JBUFFER_TRACE(jh, "ph3: write metadata");
> -               flags = jbd2_journal_write_metadata_buffer(commit_transaction,
> +               escape = jbd2_journal_write_metadata_buffer(commit_transaction,
>                                                 jh, &wbuf[bufs], blocknr);
> -               if (flags < 0) {
> -                       jbd2_journal_abort(journal, flags);
> +               if (escape < 0) {
> +                       jbd2_journal_abort(journal, escape);
>                         continue;
>                 }
>                 jbd2_file_log_bh(&io_bufs, wbuf[bufs]);
> @@ -673,7 +673,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
>                     buffer */
> 
>                 tag_flag = 0;
> -               if (flags & 1)
> +               if (escape)
>                         tag_flag |= JBD2_FLAG_ESCAPE;
>                 if (!first_tag)
>                         tag_flag |= JBD2_FLAG_SAME_UUID;
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 08c59197c5bd..c8a1eca5caab 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -309,10 +309,8 @@ static void journal_kill_thread(journal_t *journal)
>   *
>   * Return value:
>   *  <0: Error
> - * >=0: Finished OK
> - *
> - * On success:
> - * Bit 0 set == escape performed on the data
> + *  =0: Finished OK without escape
> + *  =1: Finished OK with escape
>   */
> 
> Look forward to your reply.

Yep, looks like a fine solution to me.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR