Re: [PATCH] btrfs: qgroup: Cleanup open-coded old/new_refcnt update and read.

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

-------- Original Message  --------
Subject: Re: [PATCH] btrfs: qgroup: Cleanup open-coded old/new_refcnt 
update and read.
From: Liu Bo <bo.li.liu@oracle.com>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>
Date: 2015年03月12日 21:45

> On Thu, Mar 12, 2015 at 04:33:27PM +0800, Qu Wenruo wrote:
>> Use inline functions to do such things, to improve readability.
>
> This has actually hiden informations behind the helper function and
> old_refcnt and new_refcnt can explain themselves, I don't see any benefit.
Old/new_refcnt won't explain themselves.
In fact, it's a combination of sequence and reference number, which is 
very confusing if you don't read qgroup_shared_accouting().

This patch will hides the confusing detail, caller will only need to 
care the number to increase.

Also, I'm considering split old/new_refcnt into seq and change them to 
the delta to seq.
Current implement makes qgroup oper->seq completely meaningless.
Based on this patch, we only need some minor change to do this.

Thanks,
Qu


>
> Thanks,
>
> -liubo
>>
>> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>> ---
>>   fs/btrfs/qgroup.c | 102 ++++++++++++++++++++++++++++++++++--------------------
>>   1 file changed, 65 insertions(+), 37 deletions(-)
>>
>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>> index 97159a8..3f2a1e7 100644
>> --- a/fs/btrfs/qgroup.c
>> +++ b/fs/btrfs/qgroup.c
>> @@ -84,11 +84,58 @@ struct btrfs_qgroup {
>>
>>   	/*
>>   	 * temp variables for accounting operations
>> +	 * Refer to qgroup_shared_accouting() for details.
>>   	 */
>>   	u64 old_refcnt;
>>   	u64 new_refcnt;
>>   };
>>
>> +static void update_qg_refcnt(struct btrfs_qgroup *qg, u64 seq, int mod,
>> +			     int update_old)
>> +{
>> +	if (update_old) {
>> +		if (qg->old_refcnt < seq)
>> +			qg->old_refcnt = seq;
>> +		qg->old_refcnt += mod;
>> +	} else {
>> +		if (qg->new_refcnt < seq)
>> +			qg->new_refcnt = seq;
>> +		qg->new_refcnt += mod;
>> +	}
>> +}
>> +
>> +static void update_qg_old_refcnt(struct btrfs_qgroup *qg, u64 seq, int mod)
>> +{
>> +	update_qg_refcnt(qg, seq, mod, 1);
>> +}
>> +
>> +static void update_qg_new_refcnt(struct btrfs_qgroup *qg, u64 seq, int mod)
>> +{
>> +	update_qg_refcnt(qg, seq, mod, 0);
>> +}
>> +
>> +static inline u64 get_qg_refcnt(struct btrfs_qgroup *qg, u64 seq, int get_old)
>> +{
>> +	if (get_old) {
>> +		if (qg->old_refcnt < seq)
>> +			return 0;
>> +		return qg->old_refcnt - seq;
>> +	}
>> +	if (qg->new_refcnt < seq)
>> +		return 0;
>> +	return qg->new_refcnt - seq;
>> +}
>> +
>> +static inline u64 get_qg_old_refcnt(struct btrfs_qgroup *qg, u64 seq)
>> +{
>> +	return get_qg_refcnt(qg, seq, 1);
>> +}
>> +
>> +static inline u64 get_qg_new_refcnt(struct btrfs_qgroup *qg, u64 seq)
>> +{
>> +	return get_qg_refcnt(qg, seq, 0);
>> +}
>> +
>>   /*
>>    * glue structure to represent the relations between qgroups.
>>    */
>> @@ -1497,6 +1544,7 @@ static int qgroup_calc_old_refcnt(struct btrfs_fs_info *fs_info,
>>   		ULIST_ITER_INIT(&tmp_uiter);
>>   		while ((tmp_unode = ulist_next(tmp, &tmp_uiter))) {
>>   			struct btrfs_qgroup_list *glist;
>> +			int mod;
>>
>>   			qg = u64_to_ptr(tmp_unode->aux);
>>   			/*
>> @@ -1508,20 +1556,15 @@ static int qgroup_calc_old_refcnt(struct btrfs_fs_info *fs_info,
>>   			 * upper level qgroups in order to determine exclusive
>>   			 * counts.
>>   			 *
>> -			 * For rescan we want to set old_refcnt to seq so our
>> -			 * exclusive calculations end up correct.
>> +			 * For rescan none of the extent is recorded before so
>> +			 * we just don't add old_refcnt.
>>   			 */
>>   			if (rescan)
>> -				qg->old_refcnt = seq;
>> -			else if (qg->old_refcnt < seq)
>> -				qg->old_refcnt = seq + 1;
>> +				mod = 0;
>>   			else
>> -				qg->old_refcnt++;
>> -
>> -			if (qg->new_refcnt < seq)
>> -				qg->new_refcnt = seq + 1;
>> -			else
>> -				qg->new_refcnt++;
>> +				mod = 1;
>> +			update_qg_old_refcnt(qg, seq, mod);
>> +			update_qg_new_refcnt(qg, seq, 1);
>>   			list_for_each_entry(glist, &qg->groups, next_group) {
>>   				ret = ulist_add(qgroups, glist->group->qgroupid,
>>   						ptr_to_u64(glist->group),
>> @@ -1619,10 +1662,8 @@ next:
>>   			qg->old_refcnt = seq + 1;
>>   		else
>>   			qg->old_refcnt++;
>> -		if (qg->new_refcnt < seq)
>> -			qg->new_refcnt = seq + 1;
>> -		else
>> -			qg->new_refcnt++;
>> +		update_qg_old_refcnt(qg, seq, 1);
>> +		update_qg_new_refcnt(qg, seq, 1);
>>   		list_for_each_entry(glist, &qg->groups, next_group) {
>>   			ret = ulist_add(qgroups, glist->group->qgroupid,
>>   					ptr_to_u64(glist->group), GFP_ATOMIC);
>> @@ -1663,17 +1704,10 @@ static int qgroup_calc_new_refcnt(struct btrfs_fs_info *fs_info,
>>   		struct btrfs_qgroup_list *glist;
>>
>>   		qg = u64_to_ptr(unode->aux);
>> -		if (oper->type == BTRFS_QGROUP_OPER_ADD_SHARED) {
>> -			if (qg->new_refcnt < seq)
>> -				qg->new_refcnt = seq + 1;
>> -			else
>> -				qg->new_refcnt++;
>> -		} else {
>> -			if (qg->old_refcnt < seq)
>> -				qg->old_refcnt = seq + 1;
>> -			else
>> -				qg->old_refcnt++;
>> -		}
>> +		if (oper->type == BTRFS_QGROUP_OPER_ADD_SHARED)
>> +			update_qg_new_refcnt(qg, seq, 1);
>> +		else
>> +			update_qg_old_refcnt(qg, seq, 1);
>>   		list_for_each_entry(glist, &qg->groups, next_group) {
>>   			ret = ulist_add(tmp, glist->group->qgroupid,
>>   					ptr_to_u64(glist->group), GFP_ATOMIC);
>> @@ -1706,11 +1740,14 @@ static int qgroup_adjust_counters(struct btrfs_fs_info *fs_info,
>>   		bool dirty = false;
>>
>>   		qg = u64_to_ptr(unode->aux);
>> +		cur_old_count = get_qg_old_refcnt(qg, seq);
>> +		cur_new_count = get_qg_new_refcnt(qg, seq);
>> +
>>   		/*
>>   		 * Wasn't referenced before but is now, add to the reference
>>   		 * counters.
>>   		 */
>> -		if (qg->old_refcnt <= seq && qg->new_refcnt > seq) {
>> +		if (cur_old_count == 0 && cur_new_count > 0) {
>>   			qg->rfer += num_bytes;
>>   			qg->rfer_cmpr += num_bytes;
>>   			dirty = true;
>> @@ -1720,21 +1757,12 @@ static int qgroup_adjust_counters(struct btrfs_fs_info *fs_info,
>>   		 * Was referenced before but isn't now, subtract from the
>>   		 * reference counters.
>>   		 */
>> -		if (qg->old_refcnt > seq && qg->new_refcnt <= seq) {
>> +		if (cur_old_count > 0 && cur_new_count == 0) {
>>   			qg->rfer -= num_bytes;
>>   			qg->rfer_cmpr -= num_bytes;
>>   			dirty = true;
>>   		}
>>
>> -		if (qg->old_refcnt < seq)
>> -			cur_old_count = 0;
>> -		else
>> -			cur_old_count = qg->old_refcnt - seq;
>> -		if (qg->new_refcnt < seq)
>> -			cur_new_count = 0;
>> -		else
>> -			cur_new_count = qg->new_refcnt - seq;
>> -
>>   		/*
>>   		 * If our refcount was the same as the roots previously but our
>>   		 * new count isn't the same as the number of roots now then we
>> --
>> 2.3.1
>>
>> --
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