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From:   Andreas Dilger <adilger@dilger.ca>
Message-Id: <D5F6A0C1-D139-4BF9-B8C4-FE673D9CEBA4@dilger.ca>
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Subject: Re: [PATCH v2 05/12] jbd2: fast-commit commit path new APIs
Date:   Fri, 9 Aug 2019 15:11:13 -0600
In-Reply-To: <6DBCC366-02CC-4F2A-AA16-EC4587261699@dilger.ca>
Cc:     linux-ext4@vger.kernel.org
To:     Harshad Shirwadkar <harshadshirwadkar@gmail.com>
References: <20190809034552.148629-1-harshadshirwadkar@gmail.com>
 <20190809034552.148629-6-harshadshirwadkar@gmail.com>
 <6DBCC366-02CC-4F2A-AA16-EC4587261699@dilger.ca>
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> On Aug 9, 2019, at 2:38 PM, Andreas Dilger <adilger@dilger.ca> wrote:
>=20
> On Aug 8, 2019, at 9:45 PM, Harshad Shirwadkar =
<harshadshirwadkar@gmail.com> wrote:
>>=20
>> This patch adds new helper APIs that ext4 needs for fast
>> commits. These new fast commit APIs are used by subsequent fast =
commit
>> patches to implement fast commits. Following new APIs are added:
>>=20
>> /*
>> * Returns when either a full commit or a fast commit
>> * completes
>> */
>> int jbd2_fc_complete_commit(journal_tc *journal, tid_t tid,
>> 			    tid_t tid, tid_t subtid)
>>=20
>> /* Send all the data buffers related to an inode */
>> int journal_submit_inode_data(journal_t *journal,
>> 			      struct jbd2_inode *jinode)
>>=20
>> /* Map one fast commit buffer for use by the file system */
>> int jbd2_map_fc_buf(journal_t *journal, struct buffer_head **bh_out)
>>=20
>> /* Wait on fast commit buffers to complete IO */
>> jbd2_wait_on_fc_bufs(journal_t *journal, int num_bufs)
>>=20
>> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
>>=20
>> +int jbd2_map_fc_buf(journal_t *journal, struct buffer_head **bh_out)
>> +{
>> +	unsigned long long pblock;
>> +	unsigned long blocknr;
>> +	int ret =3D 0;
>> +	struct buffer_head *bh;
>> +	int fc_off;
>> +	journal_header_t *jhdr;
>> +
>> +	write_lock(&journal->j_state_lock);
>> +
>> +	if (journal->j_fc_off + journal->j_first_fc < =
journal->j_last_fc) {
>> +		fc_off =3D journal->j_fc_off;
>> +		blocknr =3D journal->j_first_fc + fc_off;
>> +		journal->j_fc_off++;
>> +	} else {
>> +		ret =3D -EINVAL;
>> +	}
>> +	write_unlock(&journal->j_state_lock);
>> +
>> +	if (ret)
>> +		return ret;
>> +
>> +	ret =3D jbd2_journal_bmap(journal, blocknr, &pblock);
>> +	if (ret)
>> +		return ret;
>> +
>> +	bh =3D __getblk(journal->j_dev, pblock, journal->j_blocksize);
>> +	if (!bh)
>> +		return -ENOMEM;
>> +
>> +	lock_buffer(bh);
>> +	jhdr =3D (journal_header_t *)bh->b_data;
>> +	jhdr->h_magic =3D cpu_to_be32(JBD2_MAGIC_NUMBER);
>> +	jhdr->h_blocktype =3D cpu_to_be32(JBD2_FC_BLOCK);
>> +	jhdr->h_sequence =3D =
cpu_to_be32(journal->j_running_transaction->t_tid);
>> +
>> +	set_buffer_uptodate(bh);
>> +	unlock_buffer(bh);
>> +	journal->j_fc_wbuf[fc_off] =3D bh;
>> +
>> +	*bh_out =3D bh;
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL(jbd2_map_fc_buf);

One question about this function.  It seems that it is called for every
commit by ext4_journal_fc_commit_cb().  Why does it need to map the fast
journal commit blocks on every call?  It would make more sense to map =
the
blocks once at initialization time and then just re-use them on each =
call.

Cheers, Andreas


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