linux-ext4 - Re: [PATCH -v3] ext4: optimize ext4_should_retry

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Date:	Wed, 6 Jul 2016 14:43:46 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH -v3] ext4: optimize ext4_should_retry_alloc() to improve
 ENOSPC performance

On Thu 30-06-16 11:00:31, Ted Tso wrote:
> If there are no pending blocks to be released after a commit, forcing
> a journal commit has no hope of helping.  It's possible that a commit
> had just completed, so if there are now free blocks available for
> allocation, it's worth retrying the commit.
> 
> Reported-by: Chao Yu <yuchao0@...wei.com>
> Signed-off-by: Theodore Ts'o <tytso@....edu>

The patch looks good now. Feel free to add:

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

I'd just remove ext4_journal_callback_add() function since it is unused now
and if Lustre uses it, it can easily replicate it.

								Honza
> ---
>  fs/ext4/balloc.c    |  4 +++-
>  fs/ext4/ext4.h      |  1 +
>  fs/ext4/ext4_jbd2.h | 10 +++++++++-
>  fs/ext4/mballoc.c   | 12 ++++++++++--
>  4 files changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> index 3020fd7..0b8105b 100644
> --- a/fs/ext4/balloc.c
> +++ b/fs/ext4/balloc.c
> @@ -610,7 +610,9 @@ int ext4_should_retry_alloc(struct super_block *sb, int *retries)
>  
>  	jbd_debug(1, "%s: retrying operation after ENOSPC\n", sb->s_id);
>  
> -	jbd2_journal_force_commit_nested(EXT4_SB(sb)->s_journal);
> +	smp_mb();
> +	if (EXT4_SB(sb)->s_mb_free_pending)
> +		jbd2_journal_force_commit_nested(EXT4_SB(sb)->s_journal);
>  	return 1;
>  }
>  
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index b84aa1c..96c73e6 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1430,6 +1430,7 @@ struct ext4_sb_info {
>  	unsigned short *s_mb_offsets;
>  	unsigned int *s_mb_maxs;
>  	unsigned int s_group_info_size;
> +	unsigned int s_mb_free_pending;
>  
>  	/* tunables */
>  	unsigned long s_stripe;
> diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
> index 09c1ef3..b1d52c1 100644
> --- a/fs/ext4/ext4_jbd2.h
> +++ b/fs/ext4/ext4_jbd2.h
> @@ -175,6 +175,13 @@ struct ext4_journal_cb_entry {
>   * There is no guaranteed calling order of multiple registered callbacks on
>   * the same transaction.
>   */
> +static inline void _ext4_journal_callback_add(handle_t *handle,
> +			struct ext4_journal_cb_entry *jce)
> +{
> +	/* Add the jce to transaction's private list */
> +	list_add_tail(&jce->jce_list, &handle->h_transaction->t_private_list);
> +}
> +
>  static inline void ext4_journal_callback_add(handle_t *handle,
>  			void (*func)(struct super_block *sb,
>  				     struct ext4_journal_cb_entry *jce,
> @@ -187,10 +194,11 @@ static inline void ext4_journal_callback_add(handle_t *handle,
>  	/* Add the jce to transaction's private list */
>  	jce->jce_func = func;
>  	spin_lock(&sbi->s_md_lock);
> -	list_add_tail(&jce->jce_list, &handle->h_transaction->t_private_list);
> +	_ext4_journal_callback_add(handle, jce);
>  	spin_unlock(&sbi->s_md_lock);
>  }
>  
> +
>  /**
>   * ext4_journal_callback_del: delete a registered callback
>   * @handle: active journal transaction handle on which callback was registered
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index c1ab3ec..77249e1 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2627,6 +2627,7 @@ int ext4_mb_init(struct super_block *sb)
>  
>  	spin_lock_init(&sbi->s_md_lock);
>  	spin_lock_init(&sbi->s_bal_lock);
> +	sbi->s_mb_free_pending = 0;
>  
>  	sbi->s_mb_max_to_scan = MB_DEFAULT_MAX_TO_SCAN;
>  	sbi->s_mb_min_to_scan = MB_DEFAULT_MIN_TO_SCAN;
> @@ -2814,6 +2815,9 @@ static void ext4_free_data_callback(struct super_block *sb,
>  	/* we expect to find existing buddy because it's pinned */
>  	BUG_ON(err != 0);
>  
> +	spin_lock(&EXT4_SB(sb)->s_md_lock);
> +	EXT4_SB(sb)->s_mb_free_pending -= entry->efd_count;
> +	spin_unlock(&EXT4_SB(sb)->s_md_lock);
>  
>  	db = e4b.bd_info;
>  	/* there are blocks to put in buddy to make them really free */
> @@ -4583,6 +4587,7 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
>  {
>  	ext4_group_t group = e4b->bd_group;
>  	ext4_grpblk_t cluster;
> +	ext4_grpblk_t clusters = new_entry->efd_count;
>  	struct ext4_free_data *entry;
>  	struct ext4_group_info *db = e4b->bd_info;
>  	struct super_block *sb = e4b->bd_sb;
> @@ -4649,8 +4654,11 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
>  		}
>  	}
>  	/* Add the extent to transaction's private list */
> -	ext4_journal_callback_add(handle, ext4_free_data_callback,
> -				  &new_entry->efd_jce);
> +	new_entry->efd_jce.jce_func = ext4_free_data_callback;
> +	spin_lock(&sbi->s_md_lock);
> +	_ext4_journal_callback_add(handle, &new_entry->efd_jce);
> +	sbi->s_mb_free_pending += clusters;
> +	spin_unlock(&sbi->s_md_lock);
>  	return 0;
>  }
>  
> -- 
> 2.5.0
> 
> --
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-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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