linux-ext4 - Re: [PATCH 6/7] jbd2: Use a folio in jbd2_journal_write_metadata

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Date:   Mon, 31 Jul 2023 16:43:16 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Sterba <dsterba@...e.com>, linux-fsdevel@...r.kernel.org,
        Pankaj Raghav <p.raghav@...sung.com>,
        Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
        ntfs3@...ts.linux.dev, Theodore Tso <tytso@....edu>,
        Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 6/7] jbd2: Use a folio in
 jbd2_journal_write_metadata_buffer()

On Thu 13-07-23 04:55:11, Matthew Wilcox (Oracle) wrote:
> The primary goal here is removing the use of set_bh_page().
> Take the opportunity to switch from kmap_atomic() to kmap_local().
> This simplifies the function as the offset is already added to
> the pointer.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

Looks good. Feel free to add:

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

							Honza

> ---
>  fs/jbd2/journal.c | 35 ++++++++++++++++-------------------
>  1 file changed, 16 insertions(+), 19 deletions(-)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index fbce16fedaa4..1b5a45ab62b0 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -341,7 +341,7 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  	int do_escape = 0;
>  	char *mapped_data;
>  	struct buffer_head *new_bh;
> -	struct page *new_page;
> +	struct folio *new_folio;
>  	unsigned int new_offset;
>  	struct buffer_head *bh_in = jh2bh(jh_in);
>  	journal_t *journal = transaction->t_journal;
> @@ -370,14 +370,14 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  	 */
>  	if (jh_in->b_frozen_data) {
>  		done_copy_out = 1;
> -		new_page = virt_to_page(jh_in->b_frozen_data);
> -		new_offset = offset_in_page(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);
>  	} else {
> -		new_page = jh2bh(jh_in)->b_page;
> -		new_offset = offset_in_page(jh2bh(jh_in)->b_data);
> +		new_folio = jh2bh(jh_in)->b_folio;
> +		new_offset = offset_in_folio(new_folio, jh2bh(jh_in)->b_data);
>  	}
>  
> -	mapped_data = kmap_atomic(new_page);
> +	mapped_data = kmap_local_folio(new_folio, new_offset);
>  	/*
>  	 * Fire data frozen trigger if data already wasn't frozen.  Do this
>  	 * before checking for escaping, as the trigger may modify the magic
> @@ -385,18 +385,17 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  	 * data in the buffer.
>  	 */
>  	if (!done_copy_out)
> -		jbd2_buffer_frozen_trigger(jh_in, mapped_data + new_offset,
> +		jbd2_buffer_frozen_trigger(jh_in, mapped_data,
>  					   jh_in->b_triggers);
>  
>  	/*
>  	 * Check for escaping
>  	 */
> -	if (*((__be32 *)(mapped_data + new_offset)) ==
> -				cpu_to_be32(JBD2_MAGIC_NUMBER)) {
> +	if (*((__be32 *)mapped_data) == cpu_to_be32(JBD2_MAGIC_NUMBER)) {
>  		need_copy_out = 1;
>  		do_escape = 1;
>  	}
> -	kunmap_atomic(mapped_data);
> +	kunmap_local(mapped_data);
>  
>  	/*
>  	 * Do we need to do a data copy?
> @@ -417,12 +416,10 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  		}
>  
>  		jh_in->b_frozen_data = tmp;
> -		mapped_data = kmap_atomic(new_page);
> -		memcpy(tmp, mapped_data + new_offset, bh_in->b_size);
> -		kunmap_atomic(mapped_data);
> +		memcpy_from_folio(tmp, new_folio, new_offset, bh_in->b_size);
>  
> -		new_page = virt_to_page(tmp);
> -		new_offset = offset_in_page(tmp);
> +		new_folio = virt_to_folio(tmp);
> +		new_offset = offset_in_folio(new_folio, tmp);
>  		done_copy_out = 1;
>  
>  		/*
> @@ -438,12 +435,12 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
>  	 * copying, we can finally do so.
>  	 */
>  	if (do_escape) {
> -		mapped_data = kmap_atomic(new_page);
> -		*((unsigned int *)(mapped_data + new_offset)) = 0;
> -		kunmap_atomic(mapped_data);
> +		mapped_data = kmap_local_folio(new_folio, new_offset);
> +		*((unsigned int *)mapped_data) = 0;
> +		kunmap_local(mapped_data);
>  	}
>  
> -	set_bh_page(new_bh, new_page, new_offset);
> +	folio_set_bh(new_bh, new_folio, new_offset);
>  	new_bh->b_size = bh_in->b_size;
>  	new_bh->b_bdev = journal->j_dev;
>  	new_bh->b_blocknr = blocknr;
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR