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From:   Andreas Dilger <adilger@dilger.ca>
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Subject: Re: [PATCH v2 03/12] jbd2: fast commit setup and enable
Date:   Fri, 9 Aug 2019 14:02:13 -0600
In-Reply-To: <20190809034552.148629-4-harshadshirwadkar@gmail.com>
Cc:     linux-ext4@vger.kernel.org
To:     Harshad Shirwadkar <harshadshirwadkar@gmail.com>
References: <20190809034552.148629-1-harshadshirwadkar@gmail.com>
 <20190809034552.148629-4-harshadshirwadkar@gmail.com>
Sender: linux-ext4-owner@vger.kernel.org
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On Aug 8, 2019, at 9:45 PM, Harshad Shirwadkar =
<harshadshirwadkar@gmail.com> wrote:
>=20
> This patch allows file systems to turn fast commits on and thereby
> restrict the normal journalling space to total journal blocks minus
> JBD2_FAST_COMMIT_BLOCKS. Fast commits are not actually performed, just
> the interface to turn fast commits on is opened.
>=20
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
>=20
> ---
>=20
> Changelog:
>=20
> V2: No changes since V1
> ---
> fs/ext4/super.c      |  3 ++-
> fs/jbd2/journal.c    | 39 ++++++++++++++++++++++++++++++++-------
> fs/ocfs2/journal.c   |  4 ++--
> include/linux/jbd2.h |  2 +-
> 4 files changed, 37 insertions(+), 11 deletions(-)
>=20
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index e376ac040cce..81c3ec165822 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4933,7 +4933,8 @@ static int ext4_load_journal(struct super_block =
*sb,
> 		if (save)
> 			memcpy(save, ((char *) es) +
> 			       EXT4_S_ERR_START, EXT4_S_ERR_LEN);
> -		err =3D jbd2_journal_load(journal);
> +		err =3D jbd2_journal_load(journal,
> +					test_opt2(sb, =
JOURNAL_FAST_COMMIT));
> 		if (save)
> 			memcpy(((char *) es) + EXT4_S_ERR_START,
> 			       save, EXT4_S_ERR_LEN);
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 953990eb70a9..59ad709154a3 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1159,12 +1159,15 @@ static journal_t *journal_init_common(struct =
block_device *bdev,
> 	journal->j_blk_offset =3D start;
> 	journal->j_maxlen =3D len;
> 	n =3D journal->j_blocksize / sizeof(journal_block_tag_t);
> -	journal->j_wbufsize =3D n;
> +	journal->j_wbufsize =3D n - JBD2_FAST_COMMIT_BLOCKS;

The reservation of the JBD2_FAST_COMMIT_BLOCKS should only be done in
the case of the FAST_COMMIT feature being enabled.  Otherwise it can
hurt performance for filesystems where this feature is not enabled.

Cheers, Andreas

> 	journal->j_wbuf =3D kmalloc_array(n, sizeof(struct buffer_head =
*),
> 					GFP_KERNEL);
> 	if (!journal->j_wbuf)
> 		goto err_cleanup;
>=20
> +	journal->j_fc_wbuf =3D &journal->j_wbuf[journal->j_wbufsize];
> +	journal->j_fc_wbufsize =3D JBD2_FAST_COMMIT_BLOCKS;
> +
> 	bh =3D getblk_unmovable(journal->j_dev, start, =
journal->j_blocksize);
> 	if (!bh) {
> 		pr_err("%s: Cannot get buffer for journal superblock\n",
> @@ -1297,11 +1300,19 @@ static int journal_reset(journal_t *journal)
> 	}
>=20
> 	journal->j_first =3D first;
> -	journal->j_last =3D last;
>=20
> -	journal->j_head =3D first;
> -	journal->j_tail =3D first;
> -	journal->j_free =3D last - first;
> +	if (jbd2_has_feature_fast_commit(journal)) {
> +		journal->j_last_fc =3D last;
> +		journal->j_last =3D last - JBD2_FAST_COMMIT_BLOCKS;
> +		journal->j_first_fc =3D journal->j_last + 1;
> +		journal->j_fc_off =3D 0;
> +	} else {
> +		journal->j_last =3D last;
> +	}
> +
> +	journal->j_head =3D journal->j_first;
> +	journal->j_tail =3D journal->j_first;
> +	journal->j_free =3D journal->j_last - journal->j_first;
>=20
> 	journal->j_tail_sequence =3D journal->j_transaction_sequence;
> 	journal->j_commit_sequence =3D journal->j_transaction_sequence - =
1;
> @@ -1626,9 +1637,17 @@ static int load_superblock(journal_t *journal)
> 	journal->j_tail_sequence =3D be32_to_cpu(sb->s_sequence);
> 	journal->j_tail =3D be32_to_cpu(sb->s_start);
> 	journal->j_first =3D be32_to_cpu(sb->s_first);
> -	journal->j_last =3D be32_to_cpu(sb->s_maxlen);
> 	journal->j_errno =3D be32_to_cpu(sb->s_errno);
>=20
> +	if (jbd2_has_feature_fast_commit(journal)) {
> +		journal->j_last_fc =3D be32_to_cpu(sb->s_maxlen);
> +		journal->j_last =3D journal->j_last_fc - =
JBD2_FAST_COMMIT_BLOCKS;
> +		journal->j_first_fc =3D journal->j_last + 1;
> +		journal->j_fc_off =3D 0;
> +	} else {
> +		journal->j_last =3D be32_to_cpu(sb->s_maxlen);
> +	}
> +
> 	return 0;
> }
>=20
> @@ -1641,7 +1660,7 @@ static int load_superblock(journal_t *journal)
>  * a journal, read the journal from disk to initialise the in-memory
>  * structures.
>  */
> -int jbd2_journal_load(journal_t *journal)
> +int jbd2_journal_load(journal_t *journal, bool enable_fc)
> {
> 	int err;
> 	journal_superblock_t *sb;
> @@ -1684,6 +1703,12 @@ int jbd2_journal_load(journal_t *journal)
> 		return -EFSCORRUPTED;
> 	}
>=20
> +	if (enable_fc)
> +		jbd2_journal_set_features(journal, 0, 0,
> +					  =
JBD2_FEATURE_INCOMPAT_FAST_COMMIT);
> +	else
> +		jbd2_journal_clear_features(journal, 0, 0,
> +					    =
JBD2_FEATURE_INCOMPAT_FAST_COMMIT);
> 	/* OK, we've finished with the dynamic journal bits:
> 	 * reinitialise the dynamic contents of the superblock in memory
> 	 * and reset them on disk. */
> diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
> index 930e3d388579..3b4d91b16e8e 100644
> --- a/fs/ocfs2/journal.c
> +++ b/fs/ocfs2/journal.c
> @@ -1057,7 +1057,7 @@ int ocfs2_journal_load(struct ocfs2_journal =
*journal, int local, int replayed)
>=20
> 	osb =3D journal->j_osb;
>=20
> -	status =3D jbd2_journal_load(journal->j_journal);
> +	status =3D jbd2_journal_load(journal->j_journal, false);
> 	if (status < 0) {
> 		mlog(ML_ERROR, "Failed to load journal!\n");
> 		goto done;
> @@ -1642,7 +1642,7 @@ static int ocfs2_replay_journal(struct =
ocfs2_super *osb,
> 		goto done;
> 	}
>=20
> -	status =3D jbd2_journal_load(journal);
> +	status =3D jbd2_journal_load(journal, false);
> 	if (status < 0) {
> 		mlog_errno(status);
> 		if (!igrab(inode))
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 9a750b732241..153840b422cc 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1476,7 +1476,7 @@ extern int	   jbd2_journal_set_features
> 		   (journal_t *, unsigned long, unsigned long, unsigned =
long);
> extern void	   jbd2_journal_clear_features
> 		   (journal_t *, unsigned long, unsigned long, unsigned =
long);
> -extern int	   jbd2_journal_load       (journal_t *journal);
> +extern int	   jbd2_journal_load(journal_t *journal, bool =
enable_fc);
> extern int	   jbd2_journal_destroy    (journal_t *);
> extern int	   jbd2_journal_recover    (journal_t *journal);
> extern int	   jbd2_journal_wipe       (journal_t *, int);
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>=20


Cheers, Andreas


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