linux-kernel - Re: [PATCH v2 07/10] maple_tree: Add comments and some minor cleanups to mas_wr

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Message-ID: <8a52ce18-823c-7d75-30b7-e72a8bcf5665@bytedance.com>
Date:   Thu, 18 May 2023 17:27:02 +0800
From:   Peng Zhang <zhangpeng.00@...edance.com>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc:     Peng Zhang <zhangpeng.00@...edance.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        maple-tree@...ts.infradead.org
Subject: Re: [PATCH v2 07/10] maple_tree: Add comments and some minor cleanups
 to mas_wr_append()



在 2023/5/18 03:33, Liam R. Howlett 写道:
> * Peng Zhang <zhangpeng.00@...edance.com> [230517 04:59]:
>> Add comment for mas_wr_append(), move mas_update_gap() into
>> mas_wr_append(), and other cleanups to make mas_wr_modify() cleaner.
>>
>> Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
>> ---
>>   lib/maple_tree.c | 33 ++++++++++++++++++++-------------
>>   1 file changed, 20 insertions(+), 13 deletions(-)
>>
>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>> index 3b9d227f3d7d..bbe4c6f2858c 100644
>> --- a/lib/maple_tree.c
>> +++ b/lib/maple_tree.c
>> @@ -4308,6 +4308,12 @@ static inline unsigned char mas_wr_new_end(struct ma_wr_state *wr_mas)
>>   	return new_end;
>>   }
>>   
>> +/*
>> + * mas_wr_append: Attempt to append
>> + * @wr_mas: the maple write state
>> + *
>> + * Return: True if appended, false otherwise
>> + */
>>   static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
>>   {
>>   	unsigned char end = wr_mas->node_end;
>> @@ -4315,7 +4321,11 @@ static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
>>   	struct ma_state *mas = wr_mas->mas;
>>   	unsigned char node_pivots = mt_pivots[wr_mas->type];
>>   
>> +	if (!(mas->offset == wr_mas->node_end))
>> +		return false;
>> +
>>   	if ((mas->index != wr_mas->r_min) && (mas->last == wr_mas->r_max)) {
>> +		/* Append to end of range */
>>   		if (new_end < node_pivots)
>>   			wr_mas->pivots[new_end] = wr_mas->pivots[end];
>>   
>> @@ -4323,13 +4333,10 @@ static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
>>   			ma_set_meta(wr_mas->node, maple_leaf_64, 0, new_end);
>>   
>>   		rcu_assign_pointer(wr_mas->slots[new_end], wr_mas->entry);
>> -		mas->offset = new_end;
>>   		wr_mas->pivots[end] = mas->index - 1;
>> -
>> -		return true;
>> -	}
>> -
>> -	if ((mas->index == wr_mas->r_min) && (mas->last < wr_mas->r_max)) {
>> +		mas->offset = new_end;
>> +	} else if ((mas->index == wr_mas->r_min) && (mas->last < wr_mas->r_max)) {
>> +		/* Append to start of range */
>>   		if (new_end < node_pivots)
>>   			wr_mas->pivots[new_end] = wr_mas->pivots[end];
>>   
>> @@ -4339,10 +4346,13 @@ static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
>>   
>>   		wr_mas->pivots[end] = mas->last;
>>   		rcu_assign_pointer(wr_mas->slots[end], wr_mas->entry);
>> -		return true;
>> +	} else {
>> +		return false;
> 
> I don't think we can get here with your changes, what do you think?  If
> so, we can move the metadata setting to the outside of the if/else.  I
> checked by adding a BUG_ON() and the test code never gets here.
> 
> My thinking is, we know offset == node_end and new_end == node_end + 1..
> so we must be inserting into the last slot and only adding one entry.
Yes, I'll address this in v3. Thanks.
> 
>>   	}
>>   
>> -	return false;
>> +	if (!wr_mas->content || !wr_mas->entry)
>> +		mas_update_gap(mas);
>> +	return  true;
>>   }
>>   
>>   /*
>> @@ -4382,12 +4392,9 @@ static inline void mas_wr_modify(struct ma_wr_state *wr_mas)
>>   	if (new_end >= mt_slots[wr_mas->type])
>>   		goto slow_path;
>>   
>> -	if (wr_mas->entry && (wr_mas->node_end < mt_slots[wr_mas->type] - 1) &&
>> -	    (mas->offset == wr_mas->node_end) && mas_wr_append(wr_mas)) {
>> -		if (!wr_mas->content || !wr_mas->entry)
>> -			mas_update_gap(mas);
>> +	/* Attempt to append */
>> +	if (new_end == wr_mas->node_end + 1 && mas_wr_append(wr_mas))
>>   		return;
>> -	}
>>   
>>   	if ((wr_mas->offset_end - mas->offset <= 1) && mas_wr_slot_store(wr_mas))
>>   		return;
>> -- 
>> 2.20.1
>>