linux-kernel - Re: [PATCH v2 6/8] ext4: move escape handle to futher improve jbd2_journal_write_metadata

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Message-ID: <20240731120017.m7jsl3vbsrempupv@quack3>
Date: Wed, 31 Jul 2024 14:00:17 +0200
From: Jan Kara <jack@...e.cz>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: tytso@....edu, jack@...e.com, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/8] ext4: move escape handle to futher improve
 jbd2_journal_write_metadata_buffer

On Wed 31-07-24 14:22:45, Kemeng Shi wrote:
> Move escape handle to futher improve code readability and remove some
> repeat check.
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
> Suggested-by: Jan Kara <jack@...e.cz>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/jbd2/journal.c | 49 +++++++++++++++++++++++------------------------
>  1 file changed, 24 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index f17d05bc61df..85273fb1accb 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -281,6 +281,16 @@ static void journal_kill_thread(journal_t *journal)
>  	write_unlock(&journal->j_state_lock);
>  }
>  
> +static inline bool jbd2_data_needs_escaping(char *data)
> +{
> +	return *((__be32 *)data) == cpu_to_be32(JBD2_MAGIC_NUMBER);
> +}
> +
> +static inline void jbd2_data_do_escape(char *data)
> +{
> +	*((unsigned int *)data) = 0;
> +}
> +
>  /*
>   * jbd2_journal_write_metadata_buffer: write a metadata buffer to the journal.
>   *
> @@ -319,7 +329,6 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  				  sector_t blocknr)
>  {
>  	int do_escape = 0;
> -	char *mapped_data;
>  	struct buffer_head *new_bh;
>  	struct folio *new_folio;
>  	unsigned int new_offset;
> @@ -350,8 +359,13 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  	if (jh_in->b_frozen_data) {
>  		new_folio = virt_to_folio(jh_in->b_frozen_data);
>  		new_offset = offset_in_folio(new_folio, jh_in->b_frozen_data);
> -		mapped_data = jh_in->b_frozen_data;
> +		do_escape = jbd2_data_needs_escaping(jh_in->b_frozen_data);
> +		if (do_escape)
> +			jbd2_data_do_escape(jh_in->b_frozen_data);
>  	} else {
> +		char *tmp;
> +		char *mapped_data;
> +
>  		new_folio = bh_in->b_folio;
>  		new_offset = offset_in_folio(new_folio, bh_in->b_data);
>  		mapped_data = kmap_local_folio(new_folio, new_offset);
> @@ -363,21 +377,13 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  		 */
>  		jbd2_buffer_frozen_trigger(jh_in, mapped_data,
>  					   jh_in->b_triggers);
> -	}
> -
> -	/*
> -	 * Check for escaping
> -	 */
> -	if (*((__be32 *)mapped_data) == cpu_to_be32(JBD2_MAGIC_NUMBER))
> -		do_escape = 1;
> -	if (!jh_in->b_frozen_data)
> +		do_escape = jbd2_data_needs_escaping(mapped_data);
>  		kunmap_local(mapped_data);
> -
> -	/*
> -	 * Do we need to do a data copy?
> -	 */
> -	if (do_escape && !jh_in->b_frozen_data) {
> -		char *tmp;
> +		/*
> +		 * Do we need to do a data copy?
> +		 */
> +		if (!do_escape)
> +			goto escape_done;
>  
>  		spin_unlock(&jh_in->b_state_lock);
>  		tmp = jbd2_alloc(bh_in->b_size, GFP_NOFS);
> @@ -404,17 +410,10 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  copy_done:
>  		new_folio = virt_to_folio(jh_in->b_frozen_data);
>  		new_offset = offset_in_folio(new_folio, jh_in->b_frozen_data);
> +		jbd2_data_do_escape(jh_in->b_frozen_data);
>  	}
>  
> -	/*
> -	 * Did we need to do an escaping?  Now we've done all the
> -	 * copying, we can finally do so.
> -	 * b_frozen_data is from jbd2_alloc() which always provides an
> -	 * address from the direct kernels mapping.
> -	 */
> -	if (do_escape)
> -		*((unsigned int *)jh_in->b_frozen_data) = 0;
> -
> +escape_done:
>  	folio_set_bh(new_bh, new_folio, new_offset);
>  	new_bh->b_size = bh_in->b_size;
>  	new_bh->b_bdev = journal->j_dev;
> -- 
> 2.30.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR