Date:	Thu, 10 Feb 2011 07:58:13 -0700
From:	tm@....ma
To:	"Lukas Czerner" <lczerner@...hat.com>
Cc:	"Tao Ma" <tm@....ma>, linux-ext4@...r.kernel.org,
	"Andreas Dilger" <adilger.kernel@...ger.ca>,
	"Lukas Czerner" <lczerner@...hat.com>
Subject: Re: [PATCH 4/4 v2] ext4: Speed up FITRIM by recording flags in
 ext4_group_info.

> On Thu, 10 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.
>>
>> A simple test with my intel x25m ssd:
>> df -h shows:
>> /dev/sdb2             108G   35G   68G  34% /mnt/ext4
>> Block size:               4096
>>
>> run the FITRIM with the following parameter:
>> range.start = 0;
>> range.len = UINT64_MAX;
>> range.minlen = 1048576;
>>
>> without the patch:
>> [root@...u-tm test]# time ./ftrim /mnt/ext4/a
>> real	0m4.039s
>> user	0m0.000s
>> sys	0m1.020s
>> [root@...u-tm test]# time ./ftrim /mnt/ext4/a
>> real	0m3.577s
>> user	0m0.001s
>> sys	0m1.004s
>> [root@...u-tm test]# time ./ftrim /mnt/ext4/a
>> real	0m3.380s
>> user	0m0.000s
>> sys	0m0.991s
>>
>> with the patch:
>> [root@...u-tm test]# time ./ftrim /mnt/ext4/a
>> real	0m3.466s
>> user	0m0.000s
>> sys	0m0.966s
>> [root@...u-tm test]# time ./ftrim /mnt/ext4/a
>> real	0m0.001s
>> user	0m0.000s
>> sys	0m0.001s
>> [root@...u-tm test]# time ./ftrim /mnt/ext4/a
>> real	0m0.001s
>> user	0m0.000s
>> sys	0m0.000s
>>
>> A big improvement for the 2nd and 3rd run.
>>
>> After I delete some big image files and re-run the trim,
>> it is still much faster than iterating the whole disk.
>> /dev/sdb2             108G   25G   78G  24% /mnt/ext4
>>
>> [root@...u-tm test]# time ./ftrim /mnt/ext4/a
>> real	0m0.513s
>> user	0m0.000s
>> sys	0m0.069s
>
> Great it looks really good.
>
>>
>> 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..1d59a63 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 s_last_trim_minblks;
>>  };
>>
>>  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_WAS_TRIMMED_BIT		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_WAS_TRIMMED_BIT, &((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..c7aa094 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -2687,6 +2687,16 @@ 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_WAS_TRIMMED_BIT,
>> +				  &(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 +4782,10 @@ 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)->s_last_trim_minblks)
>> +		goto out;
>> +
>>  	trace_ext4_trim_all_free(sb, group, start, max);
>>
>>  	while (start < max) {
>> @@ -4804,6 +4818,11 @@ 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_WAS_TRIMMED_BIT,
>> +			&(e4b->bd_info->bb_state));
>> +out:
>>  	ext4_unlock_group(sb, group);
>>
>>  	ext4_debug("trimmed %d blocks in the group %d\n",
>> @@ -4892,6 +4911,9 @@ int ext4_trim_fs(struct super_block *sb, struct
>> fstrim_range *range)
>>  	}
>>  	range->len = trimmed * sb->s_blocksize;
>>
>> +	if (!ret)
>> +		EXT4_SB(sb)->s_last_trim_minblks = minlen;
>> +
>
> Since this is not protected by any lock, would not it race in case of
> multiple FITRIM calls ?
yeah, I am also thinking of this, but I don't think we need a new lock
just for this. And I guess atomic_t isn't good here because minlen is a
u64.

Do you think we can use some other spin_lock in ext4 system? I am not
quite familiar with ext4 by now, so do you have any suggestion?

Regards,
Tao


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