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SubjectRe: [PATCH] maple_tree: Avoid checking other gaps after getting the largest gap
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在 2023/12/19 04:28, Liam R. Howlett 写道:
> * Liam R. Howlett <Liam.Howlett@Oracle.com> [231218 15:20]:
>> * Peng Zhang <zhangpeng.00@bytedance.com> [231215 02:46]:
>>> The last range stored in maple tree is typically quite large. By
>>> checking if it exceeds the sum of the remaining ranges in that node, it
>>> is possible to avoid checking all other gaps.
>>>
>>> Running the maple tree test suite in user mode almost always results in
>>> a near 100% hit rate for this optimization.
>>
>> This should only be triggered for right-most nodes and root though,
>> correct (mas->max == ULONG_MAX from just before this)?
Yes, only for right-most nodes and root.
>>
>> I wonder if it's worth special case checking the first gap if the node
>> min is 0 as well. Might be worth looking at, but this patch is
>> certainly worth doing.
>
> Actually, not just when the min is 0, we have a special case close to
> here for slot 0 so we could just check the same sort of thing there.
I think that the first slot in a node does not have any special
significance. It has a lower probability of being the largest gap,
so it may not be worth considering.
>
>>
>>>
>>> Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
>>
>> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
>>
>>> ---
>>> lib/maple_tree.c | 3 +++
>>> 1 file changed, 3 insertions(+)
>>>
>>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>>> index c9a970ea20dd..6f241bb38799 100644
>>> --- a/lib/maple_tree.c
>>> +++ b/lib/maple_tree.c
>>> @@ -1518,6 +1518,9 @@ static unsigned long mas_leaf_max_gap(struct ma_state *mas)
>>> gap = ULONG_MAX - pivots[max_piv];
>>> if (gap > max_gap)
>>> max_gap = gap;
>>> +
>>> + if (max_gap > pivots[max_piv] - mas->min)
>>> + return max_gap;
>>> }
>>>
>>> for (; i <= max_piv; i++) {
>>> --
>>> 2.20.1
>>>
>

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