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Message-ID: <13a3e7cd-b8bf-1aef-b2f0-465ee77f8638@bytedance.com>
Date:   Thu, 18 May 2023 17:27:32 +0800
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Subject: Re: [PATCH v2 08/10] maple_tree: Rework mas_wr_slot_store() to be
 cleaner and more efficient.
To:     "Liam R. Howlett" <Liam.Howlett@Oracle.com>
References: <20230517085809.86522-1-zhangpeng.00@bytedance.com>
 <20230517085809.86522-9-zhangpeng.00@bytedance.com>
 <20230517224812.knkhqmrweggsbnuk@revolver>
Cc:     Peng Zhang <zhangpeng.00@bytedance.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, maple-tree@lists.infradead.org,
        linux-kernel@vger.kernel.org
From:   Peng Zhang <zhangpeng.00@bytedance.com>
In-Reply-To: <20230517224812.knkhqmrweggsbnuk@revolver>
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在 2023/5/18 06:48, Liam R. Howlett 写道:
> * Peng Zhang <zhangpeng.00@bytedance.com> [230517 04:59]:
>> The code of mas_wr_slot_store() is messy, make it clearer and concise,
>> and add comments. In addition, get whether the two gaps are empty to
>> avoid calling mas_update_gap() all the time.
>>
>> Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
>> ---
>>   lib/maple_tree.c | 59 ++++++++++++++++++++----------------------------
>>   1 file changed, 24 insertions(+), 35 deletions(-)
>>
>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>> index bbe4c6f2858c..25a8b7d5d598 100644
>> --- a/lib/maple_tree.c
>> +++ b/lib/maple_tree.c
>> @@ -4200,49 +4200,38 @@ static inline bool mas_wr_node_store(struct ma_wr_state *wr_mas)
>>   static inline bool mas_wr_slot_store(struct ma_wr_state *wr_mas)
>>   {
>>   	struct ma_state *mas = wr_mas->mas;
>> -	unsigned long lmax; /* Logical max. */
>>   	unsigned char offset = mas->offset;
>> +	unsigned char offset_end = wr_mas->offset_end;
>> +	unsigned long lmax = wr_mas->end_piv; /* Logical max. */
>> +	bool gap = false;
>>   
>> -	if ((wr_mas->r_max > mas->last) && ((wr_mas->r_min != mas->index) ||
>> -				  (offset != wr_mas->node_end)))
>> +	if (offset_end - offset != 1)
>>   		return false;
>>   
>> -	if (offset == wr_mas->node_end - 1)
>> -		lmax = mas->max;
>> -	else
>> -		lmax = wr_mas->pivots[offset + 1];
>> -
>> -	/* going to overwrite too many slots. */
>> -	if (lmax < mas->last)
>> -		return false;
>> -
>> -	if (wr_mas->r_min == mas->index) {
>> -		/* overwriting two or more ranges with one. */
>> -		if (lmax == mas->last)
>> -			return false;
>> -
>> -		/* Overwriting all of offset and a portion of offset + 1. */
>> +	if (mas->index == wr_mas->r_min && mas->last < lmax) {
>> +		/* Overwriting the range and over a part of the next range. */
>> +		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset);
>> +		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset + 1);
>>   		rcu_assign_pointer(wr_mas->slots[offset], wr_mas->entry);
>>   		wr_mas->pivots[offset] = mas->last;
>> -		goto done;
>> -	}
>> -
>> -	/* Doesn't end on the next range end. */
>> -	if (lmax != mas->last)
>> +	} else if (mas->index > wr_mas->r_min && mas->last == lmax) {
>> +		/* Overwriting a part of the range and over the next range */
>> +		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset);
>> +		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset + 1);
>> +		rcu_assign_pointer(wr_mas->slots[offset + 1], wr_mas->entry);
>> +		wr_mas->pivots[offset] = mas->index - 1;
>> +		mas->offset++; /* Keep mas accurate. */
>> +	} else {
>>   		return false;
> 
> Again here, I think you have already verified this will be a slot store
> by offset_end - offset == 1 and new_end == wr_mas->node_end.
> 
> The checking of the slots for the gap could be moved outside the
> statements.  WDYT?
Yes, I'll address this in v3. Thanks.
> 
>> +	}
>>   
>> -	/* Overwriting a portion of offset and all of offset + 1 */
>> -	if ((offset + 1 < mt_pivots[wr_mas->type]) &&
>> -	    (wr_mas->entry || wr_mas->pivots[offset + 1]))
>> -		wr_mas->pivots[offset + 1] = mas->last;
>> -
>> -	rcu_assign_pointer(wr_mas->slots[offset + 1], wr_mas->entry);
>> -	wr_mas->pivots[offset] = mas->index - 1;
>> -	mas->offset++; /* Keep mas accurate. */
>> -
>> -done:
>>   	trace_ma_write(__func__, mas, 0, wr_mas->entry);
>> -	mas_update_gap(mas);
>> +	/*
>> +	 * Only update gap when the new entry is empty or there is an empty
>> +	 * entry in the original two ranges.
>> +	 */
>> +	if (!wr_mas->entry || gap)
>> +		mas_update_gap(mas);
>>   	return true;
>>   }
>>   
>> @@ -4396,7 +4385,7 @@ static inline void mas_wr_modify(struct ma_wr_state *wr_mas)
>>   	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))
>> +	if (new_end == wr_mas->node_end && mas_wr_slot_store(wr_mas))
>>   		return;
>>   	else if (mas_wr_node_store(wr_mas))
>>   		return;
>> -- 
>> 2.20.1
>>