linux-ext4 - Re: [PATCH 4/4] ext4: Speed up FITRIM by recording flags in ext4_group

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Date:	Wed, 9 Feb 2011 15:01:46 +0100 (CET)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Tao Ma <tm@....ma>
cc:	linux-ext4@...r.kernel.org,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Lukas Czerner <lczerner@...hat.com>
Subject: Re: [PATCH 4/4] ext4: Speed up FITRIM by recording flags in
 ext4_group_info.

On Wed, 9 Feb 2011, Tao Ma wrote:

> From: Tao Ma <boyu.mt@...bao.com>
> 
> In ext4, when FITRIM is called every time, we iterate all the
> groups and do trim one by one. It is a bit time wasting if the
> group has been trimmed and there is no change since the last
> trim.
> 
> So this patch adds a new flag in ext4_group_info->bb_state to
> indicate that the group has been trimmed, and it will be cleared
> if some blocks is freed(in release_blocks_on_commit). Another
> trim_minlen is added in ext4_sb_info to record the last minlen
> we use to trim the volume, so that if the caller provide a small
> one, we will go on the trim regardless of the bb_state. The idea
> is inspired by Andreas  and Lukas Czerner.

Hi Tao,

This is great, thanks for the patch! Do you have any benchmark numbers
showing how much does it improve FSTRIM time ? It seems it might help a
lot. Couple of comments bellow.

> 
> Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> Cc: Lukas Czerner <lczerner@...hat.com>
> Signed-off-by: Tao Ma <boyu.mt@...bao.com>
> ---
>  fs/ext4/ext4.h    |    8 +++++++-
>  fs/ext4/mballoc.c |   22 ++++++++++++++++++++++
>  2 files changed, 29 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 0c8d97b..684f48e 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1200,6 +1200,9 @@ struct ext4_sb_info {
>  	struct ext4_li_request *s_li_request;
>  	/* Wait multiplier for lazy initialization thread */
>  	unsigned int s_li_wait_mult;
> +
> +	/* record the last minlen when FITRIM is called. */
> +	u64 trim_minlen;

Maybe this is a bit nitpicking, but it is not very clear what is the
"trim_minlen" for. I would rather use something like
"last_trim_minblks", or similar.

>  };
>  
>  static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)
> @@ -1970,10 +1973,13 @@ struct ext4_group_info {
>  					 * 5 free 8-block regions. */
>  };
>  
> -#define EXT4_GROUP_INFO_NEED_INIT_BIT	0
> +#define EXT4_GROUP_INFO_NEED_INIT_BIT		0
> +#define EXT4_GROUP_INFO_HAS_BEEN_TRIMMED	1
>  
>  #define EXT4_MB_GRP_NEED_INIT(grp)	\
>  	(test_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &((grp)->bb_state)))
> +#define EXT4_MB_GRP_HAS_BEEN_TRIMMED(grp)	\
> +	(test_bit(EXT4_GROUP_INFO_HAS_BEEN_TRIMMED, &((grp)->bb_state)))
>  
>  #define EXT4_MAX_CONTENTION		8
>  #define EXT4_CONTENTION_THRESHOLD	2
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 4eadac8..3f6b809 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -1563,6 +1563,9 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
>  	mb_set_bits(EXT4_MB_BITMAP(e4b), ex->fe_start, len0);
>  	mb_check_buddy(e4b);
>  
> +	if (!ret)
> +		EXT4_SB(sb)->trim_minlen = minlen;
> +

Did you even tried to compile it ? "minlen" is not defined in
mb_mark_used(), also it does make sense to set trim_minlen there. Did
not you meant it to be in ext4_trim_fs ?

>  	return ret;
>  }
>  
> @@ -2687,6 +2690,16 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
>  		rb_erase(&entry->node, &(db->bb_free_root));
>  		mb_free_blocks(NULL, &e4b, entry->start_blk, entry->count);
>  
> +		/*
> +		 * Clear the trimmed flag for the group so that the next
> +		 * ext4_trim_fs can trim it.
> +		 * If the volume is mounted with -o discard, online discard
> +		 * is supported and the free blocks will be trimmed online.
> +		 */
> +		if (!test_opt(sb, DISCARD))
> +			clear_bit(EXT4_GROUP_INFO_HAS_BEEN_TRIMMED,
> +				  &(db->bb_state));
> +
>  		if (!db->bb_free_root.rb_node) {
>  			/* No more items in the per group rb tree
>  			 * balance refcounts from ext4_mb_free_metadata()
> @@ -4772,6 +4785,10 @@ ext4_grpblk_t ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
>  
>  	ext4_lock_group(sb, group);
>  
> +	if (EXT4_MB_GRP_HAS_BEEN_TRIMMED(e4b->bd_info) &&
> +	    minblocks >= EXT4_SB(sb)->trim_minlen)
> +		goto out;
> +

I think this can be placed in the ext4_trim_fs() in the for() loop so we can
avoid unnecessary call to ext4_trim_all_free.

>  	trace_ext4_trim_all_free(sb, group, start, max);
>  
>  	while (start < max) {
> @@ -4804,6 +4821,11 @@ ext4_grpblk_t ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
>  		if ((e4b->bd_info->bb_free - free_count) < minblocks)
>  			break;
>  	}
> +
> +	if (!ret)
> +		set_bit(EXT4_GROUP_INFO_HAS_BEEN_TRIMMED,
> +			&(e4b->bd_info->bb_state));
> +out:
>  	ext4_unlock_group(sb, group);
>  
>  	ext4_debug("trimmed %d blocks in the group %d\n",
> 

Thanks!
-Lukas
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