Re: [PATCH 4/4] ext4: Speed up FITRIM by recording flags in ext4_group_info.

[Tao Ma <tm@tao.ma>]

On 07/01/2011 06:09 PM, Lukas Czerner wrote:
> On Thu, 30 Jun 2011, Tao Ma wrote:
> 
>> From: Tao Ma <boyu.mt@taobao.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/sdb1              40G   21G   17G  56% /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@boyu-tm linux-2.6]# time ./ftrim /mnt/ext4/a
>> real	0m5.505s
>> user	0m0.000s
>> sys	0m1.224s
>> [root@boyu-tm linux-2.6]# time ./ftrim /mnt/ext4/a
>> real	0m5.359s
>> user	0m0.000s
>> sys	0m1.178s
>> [root@boyu-tm linux-2.6]# time ./ftrim /mnt/ext4/a
>> real	0m5.228s
>> user	0m0.000s
>> sys	0m1.151s
>>
>> with the patch:
>> [root@boyu-tm linux-2.6]# time ./ftrim /mnt/ext4/a
>> real	0m5.625s
>> user	0m0.000s
>> sys	0m1.269s
>> [root@boyu-tm linux-2.6]# time ./ftrim /mnt/ext4/a
>> real	0m0.002s
>> user	0m0.000s
>> sys	0m0.001s
>> [root@boyu-tm linux-2.6]# time ./ftrim /mnt/ext4/a
>> real	0m0.002s
>> user	0m0.000s
>> sys	0m0.001s
>>
>> A big improvement for the 2nd and 3rd run.
>>
>> Even after I delete some big image files, it is still much
>> faster than iterating the whole disk.
>>
>> [root@boyu-tm test]# time ./ftrim /mnt/ext4/a
>> real	0m1.217s
>> user	0m0.000s
>> sys	0m0.196s
> 
> Thanks for the patch Tao, I have couple of comments bellow.
> 
>>
>> Reviewed-by: Andreas Dilger <adilger.kernel@dilger.ca>
>> Signed-off-by: Tao Ma <boyu.mt@taobao.com>
>> ---
>>  fs/ext4/ext4.h    |   13 ++++++++++++-
>>  fs/ext4/mballoc.c |   20 ++++++++++++++++++++
>>  fs/ext4/super.c   |    2 ++
>>  3 files changed, 34 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>> index 1921392..5878a22 100644
>> --- a/fs/ext4/ext4.h
>> +++ b/fs/ext4/ext4.h
>> @@ -1214,6 +1214,9 @@ struct ext4_sb_info {
>>  
>>  	/* Kernel thread for multiple mount protection */
>>  	struct task_struct *s_mmp_tsk;
>> +
>> +	/* record the last minlen when FITRIM is called. */
>> +	atomic_t s_last_trim_minblks;
>>  };
>>  
>>  static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)
>> @@ -2067,11 +2070,19 @@ 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_WAS_TRIMMED(grp)	\
>> +	(test_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
>> +#define EXT4_MB_GRP_SET_TRIMMED(grp)	\
>> +	(set_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
>> +#define EXT4_MB_GRP_CLEAR_TRIMMED(grp)	\
>> +	(clear_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 a822f2a..afdd869 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -2628,6 +2628,15 @@ 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))
>> +			EXT4_MB_GRP_CLEAR_TRIMMED(db);
> 
> If the online discard failed we should probably clear the flag as well
> right ? However I am not sure how helpful it would be since it'll most
> likely fail again. Maybe we do not need to bother with that case at all,
> what do you think ?
yes, in this case, we don't have a minor chance to trim successfully
later and it will increase the time of the next FITRIM ioctl. So I guess
we can leave it as-is.
> 
>> +
>>  		if (!db->bb_free_root.rb_node) {
>>  			/* No more items in the per group rb tree
>>  			 * balance refcounts from ext4_mb_free_metadata()
>> @@ -4840,6 +4849,10 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
>>  	bitmap = e4b.bd_bitmap;
>>  
>>  	ext4_lock_group(sb, group);
>> +	if (EXT4_MB_GRP_WAS_TRIMMED(e4b.bd_info) &&
>> +	    minblocks >= atomic_read(&EXT4_SB(sb)->s_last_trim_minblks))
>> +		goto out;
>> +
>>  	start = (e4b.bd_info->bb_first_free > start) ?
>>  		e4b.bd_info->bb_first_free : start;
>>  
>> @@ -4871,6 +4884,10 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
>>  		if ((e4b.bd_info->bb_free - free_count) < minblocks)
>>  			break;
>>  	}
>> +
>> +	if (!ret)
>> +		EXT4_MB_GRP_SET_TRIMMED(e4b.bd_info);
>> +out:
>>  	ext4_unlock_group(sb, group);
>>  	ext4_mb_unload_buddy(&e4b);
>>  
>> @@ -4960,6 +4977,9 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
>>  	}
>>  	range->len = trimmed * sb->s_blocksize;
>>  
>> +	if (!ret)
>> +		atomic_set(&EXT4_SB(sb)->s_last_trim_minblks, minlen);
>> +
>>  out:
>>  	return ret;
>>  }
>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> index 9ea71aa..080e9f9 100644
>> --- a/fs/ext4/super.c
>> +++ b/fs/ext4/super.c
>> @@ -3086,6 +3086,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>>  		sbi->s_sectors_written_start =
>>  			part_stat_read(sb->s_bdev->bd_part, sectors[1]);
>>  
>> +	atomic_set(&sbi->s_last_trim_minblks, 0);
>> +
> 
> I am not sure that this is needed since sbi is allocated with kzalloc,
> so it should be zero already.
yes, maybe. I can remove it if you like.

Thanks
Tao
> 
>>  	/* Cleanup superblock name */
>>  	for (cp = sb->s_id; (cp = strchr(cp, '/'));)
>>  		*cp = '!';
>>
> 
> Thanks!
> -Lukas
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html