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Date: Thu, 17 Dec 2009 13:07:24 +0300
From: Dmitry Monakhov <dmonakhov@...nvz.org>
To: Jan Kara <jack@...e.cz>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: journalled quota seed-up
Dmitry Monakhov <dmonakhov@...nvz.org> writes:
> Dmitry Monakhov <dmonakhov@...nvz.org> writes:
>
> Sorry forgot to add linux-ext4@...r.kernel.org list to CC
>> Currently each quota modification result in write_dquot()
>> and later dquot_commit(). This means what each quota modification
>> function must wait for dqio_mutex. Which is *huge* performance
>> penalty on big SMP systems.
performance results:
simple tests-case: pwrite(,,40960,0); ftruncate(,0) in a loop
measured value: ops/ms == loops per msecond
mount: with journaled quota, and nodelalloc in order to force
curspace modification for each operation.
Seems it will be reasonable to prepare same patch for ext3.
| write-truncate | w/o quot | w jquot | w jquot mk_drt patch |
| nodelalloc | | | |
| NR tasks 1 | 20.4 | 14.5 | 14.83 |
| | 20.3 | 14.7 | 14.7 |
| | 20.4 | 14.8 | 14.8 |
| | | | |
| 4 | 6.1 | 4.76 | 6.3 |
| | 6.3 | 5.1 | 6.1 |
| | 6.5 | 4.8 | 6.3 |
| | | | |
| 8 | 3.75 | 2.59 | 3.34 |
| | 4.0 | 2.6 | 3.44 |
| | 3.76 | 2.63 | 3.47 |
>> ASAIU The core idea of this implementation
>> is to guarantee that each quota modification will be written to journal
>> atomically. But in fact this is not always true, because dquot may be
>> changed after dquot modification, but before it was committed to disk.
>>
>> | Task 1 | Task 2 |
>> | alloc_space(nr) | |
>> | ->spin_lock(dq_data_lock) | |
>> | ->curspace += nr | |
>> | ->spin_unlock(dq_data_lock) | |
>> | ->mark_dirty() | free_space(nr) |
>> | -->write_dquot() | ->spin_lock(dq_data_lock) |
>> | --->dquot_commit() | ->curspace -= nr |
>> | ---->commit_dqblk() | ->spin_unlock(dq_data_lock) |
>> | ----->spin_lock(dq_data_lock) | |
>> | ----->mem2disk_dqblk(ddq, dquot) | <<< Copy updated value |
>> | ----->spin_unlock(dq_data_lock) | |
>> | ----->quota_write() | |
>> Quota corruption not happens only because quota modification caller
>> started journal already. And ext3/4 allow only one running quota
>> at a time. Let's exploit this fact and avoid writing quota each time.
>> Act similar to dirty_for_io in general write_back path in page-cache.
>> If we have found what other task already started on copy and write the
>> dquot then we skip actual quota_write stage. And let that task do the job.
>> Side effect: Task which skip real quota_write() will not get an error
>> (if any). But this is not big deal because:
>> 1) Any error has global consequences (RO_remount, err_print, etc).
>> 2) Real IO is differed till the journall_commit.
>>
>> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
>> ---
>> fs/ext4/super.c | 37 ++++++++++++++++++++++++++++++-------
>> fs/quota/dquot.c | 16 +++++++++++++---
>> include/linux/quotaops.h | 1 +
>> 3 files changed, 44 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> index 3929091..164217e 100644
>> --- a/fs/ext4/super.c
>> +++ b/fs/ext4/super.c
>> @@ -3777,14 +3777,37 @@ static int ext4_release_dquot(struct dquot *dquot)
>>
>> static int ext4_mark_dquot_dirty(struct dquot *dquot)
>> {
>> - /* Are we journaling quotas? */
>> - if (EXT4_SB(dquot->dq_sb)->s_qf_names[USRQUOTA] ||
>> - EXT4_SB(dquot->dq_sb)->s_qf_names[GRPQUOTA]) {
>> - dquot_mark_dquot_dirty(dquot);
>> - return ext4_write_dquot(dquot);
>> - } else {
>> + int ret, err;
>> + handle_t *handle;
>> + struct inode *inode;
>> +
>> + /* Are we not journaling quotas? */
>> + if (!EXT4_SB(dquot->dq_sb)->s_qf_names[USRQUOTA] &&
>> + !EXT4_SB(dquot->dq_sb)->s_qf_names[GRPQUOTA])
>> return dquot_mark_dquot_dirty(dquot);
>> - }
>> +
>> + /* journaling quotas case */
>> + inode = dquot_to_inode(dquot);
>> + handle = ext4_journal_start(inode,
>> + EXT4_QUOTA_TRANS_BLOCKS(dquot->dq_sb));
>> + if (IS_ERR(handle))
>> + return PTR_ERR(handle);
>> + if (!__dquot_mark_dquot_dirty(dquot))
>> + ret = dquot_commit(dquot);
>> + else
>> + /*
>> + * Dquot was already dirty. This means that other task already
>> + * started a transaction but not clear dirty bit yet (see
>> + * dquot_commit). Since the only one running transaction is
>> + * possible at a time. Then that task belongs to the same
>> + * transaction. We don'n have to actually write dquot changes
>> + * because that task will write it for for us.
>> + */
>> + ret = 0;
>> + err = ext4_journal_stop(handle);
>> + if (!ret)
>> + ret = err;
>> + return ret;
>> }
>>
>> static int ext4_write_info(struct super_block *sb, int type)
>> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
>> index 6979224..e03eea0 100644
>> --- a/fs/quota/dquot.c
>> +++ b/fs/quota/dquot.c
>> @@ -311,14 +311,24 @@ static inline int mark_dquot_dirty(struct dquot *dquot)
>> {
>> return dquot->dq_sb->dq_op->mark_dirty(dquot);
>> }
>> -
>> -int dquot_mark_dquot_dirty(struct dquot *dquot)
>> +/* mark dquot dirty in atomic meaner, and return old dirty state */
>> +int __dquot_mark_dquot_dirty(struct dquot *dquot)
>> {
>> + int ret = 1;
>> spin_lock(&dq_list_lock);
>> - if (!test_and_set_bit(DQ_MOD_B, &dquot->dq_flags))
>> + if (!test_and_set_bit(DQ_MOD_B, &dquot->dq_flags)) {
>> list_add(&dquot->dq_dirty, &sb_dqopt(dquot->dq_sb)->
>> info[dquot->dq_type].dqi_dirty_list);
>> + ret = 0;
>> + }
>> spin_unlock(&dq_list_lock);
>> + return ret;
>> +}
>> +EXPORT_SYMBOL(__dquot_mark_dquot_dirty);
>> +
>> +int dquot_mark_dquot_dirty(struct dquot *dquot)
>> +{
>> + __dquot_mark_dquot_dirty(dquot);
>> return 0;
>> }
>> EXPORT_SYMBOL(dquot_mark_dquot_dirty);
>> diff --git a/include/linux/quotaops.h b/include/linux/quotaops.h
>> index ae7ef25..c950f7d 100644
>> --- a/include/linux/quotaops.h
>> +++ b/include/linux/quotaops.h
>> @@ -56,6 +56,7 @@ int dquot_commit(struct dquot *dquot);
>> int dquot_acquire(struct dquot *dquot);
>> int dquot_release(struct dquot *dquot);
>> int dquot_commit_info(struct super_block *sb, int type);
>> +int __dquot_mark_dquot_dirty(struct dquot *dquot);
>> int dquot_mark_dquot_dirty(struct dquot *dquot);
>>
>> int vfs_quota_on(struct super_block *sb, int type, int format_id,
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