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Subject: Re: [PATCH 2/9] jbd2: remove unused return info from
 jbd2_journal_write_metadata_buffer
To: Zhang Yi <yi.zhang@huaweicloud.com>
Cc: linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, tytso@mit.edu,
 jack@suse.com
References: <20240506141801.1165315-1-shikemeng@huaweicloud.com>
 <20240506141801.1165315-3-shikemeng@huaweicloud.com>
 <97dbc0cd-5676-9e92-931c-5873f2e207cd@huaweicloud.com>
From: Kemeng Shi <shikemeng@huaweicloud.com>
Message-ID: <ba9e9257-b309-17aa-9c1d-b4730bc2a91e@huaweicloud.com>
Date: Wed, 8 May 2024 09:42:30 +0800
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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@huaweicloud.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.
Thanks.
Kemeng

> 
> Thanks,
> Yi.
>