linux-kernel - Re: [PATCH 3/9] maple_tree: Modify the allocation method of mtree_alloc

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Message-ID: <1ee0cfa0-c442-1e31-24a8-90dd8b7ab2a6@gmail.com>
Date:   Wed, 26 Apr 2023 20:34:21 +0800
From:   Peng Zhang <perlyzhang@...il.com>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        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 3/9] maple_tree: Modify the allocation method of
 mtree_alloc_range/rrange()



在 2023/4/26 00:08, Liam R. Howlett 写道:
> * Peng Zhang <zhangpeng.00@...edance.com> [230425 07:05]:
>> Let mtree_alloc_range() and mtree_alloc_rrange() use mas_empty_area()
>> and mas_empty_area_rev() respectively for allocation to reduce code
>> redundancy. And after doing this, we don't need to maintain two logically
>> identical codes to improve maintainability.
>>
>> In fact, mtree_alloc_range/rrange() has some bugs. For example, when
>> dealing with min equals to max (mas_empty_area/area_rev() has been fixed),
>> the allocation will fail.
>> There are still some other bugs in it, I saw it with my naked eyes, but
>> I didn't test it, for example:
>> When mtree_alloc_range()->mas_alloc()->mas_awalk(), we set mas.index = min,
>> mas.last = max - size. However, mas_awalk() requires mas.index = min,
>> mas.last = max, which may lead to allocation failures.
> 
> Please don't re-state code in your commit messages.
> 
> Try to focus on what you did, and not why.
> 
> ie: Aligned mtree_alloc_range() to use the same internal function as
> mas_empty_area().
> 
>>
>> Right now no users are using these two functions so the bug won't trigger,
>> but this might trigger in the future.
>>
>> Also use mas_store_gfp() instead of mas_fill_gap() as I don't see any
>> difference between them.
> 
> Yeah, evolution of the code converged on the same design.  Thanks for
> seeing this.
> 
>>
>> After doing this, we no longer need the three functions
>> mas_fill_gap(), mas_alloc(), and mas_rev_alloc().
> 
> Let's just drop mtree_alloc_range() and mtree_alloc_rrange() and
> whatever else you found here.  They were planned to simplify the mmap
> code allocations, but since there would need to be arch involvement
> (coloring, etc) and alignment, etc; it is better to leave this job to
> the mm code itself.
Ok, I will remove some useless functions here.
But mtree_alloc_range() and mtree_alloc_rrange() really don't need to be 
reserved? Because I don't know if there will be users using it in other 
scenarios in the future.

Thank you for all your suggestions on this patch set, I will update them.
> 
>>
>> Fixes: 54a611b60590 ("Maple Tree: add new data structure")
>> Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
>> ---
>>   lib/maple_tree.c | 45 ++++++++++++---------------------------------
>>   1 file changed, 12 insertions(+), 33 deletions(-)
>>
>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>> index aa55c914818a0..294d4c8668323 100644
>> --- a/lib/maple_tree.c
>> +++ b/lib/maple_tree.c
>> @@ -6362,32 +6362,20 @@ int mtree_alloc_range(struct maple_tree *mt, unsigned long *startp,
>>   {
>>   	int ret = 0;
>>   
>> -	MA_STATE(mas, mt, min, max - size);
>> +	MA_STATE(mas, mt, 0, 0);
>>   	if (!mt_is_alloc(mt))
>>   		return -EINVAL;
>>   
>>   	if (WARN_ON_ONCE(mt_is_reserved(entry)))
>>   		return -EINVAL;
>>   
>> -	if (min > max)
>> -		return -EINVAL;
>> -
>> -	if (max < size)
>> -		return -EINVAL;
>> -
>> -	if (!size)
>> -		return -EINVAL;
>> -
>>   	mtree_lock(mt);
>> -retry:
>> -	mas.offset = 0;
>> -	mas.index = min;
>> -	mas.last = max - size;
>> -	ret = mas_alloc(&mas, entry, size, startp);
>> -	if (mas_nomem(&mas, gfp))
>> -		goto retry;
>> -
>> +	ret = mas_empty_area(&mas, min, max, size);
>> +	if (!ret)
>> +		ret = mas_store_gfp(&mas, entry, gfp);
>>   	mtree_unlock(mt);
>> +	if (!ret)
>> +		*startp = mas.index;
>>   	return ret;
>>   }
>>   EXPORT_SYMBOL(mtree_alloc_range);
>> @@ -6398,29 +6386,20 @@ int mtree_alloc_rrange(struct maple_tree *mt, unsigned long *startp,
>>   {
>>   	int ret = 0;
>>   
>> -	MA_STATE(mas, mt, min, max - size);
>> +	MA_STATE(mas, mt, 0, 0);
>>   	if (!mt_is_alloc(mt))
>>   		return -EINVAL;
>>   
>>   	if (WARN_ON_ONCE(mt_is_reserved(entry)))
>>   		return -EINVAL;
>>   
>> -	if (min >= max)
>> -		return -EINVAL;
>> -
>> -	if (max < size - 1)
>> -		return -EINVAL;
>> -
>> -	if (!size)
>> -		return -EINVAL;
>> -
>>   	mtree_lock(mt);
>> -retry:
>> -	ret = mas_rev_alloc(&mas, min, max, entry, size, startp);
>> -	if (mas_nomem(&mas, gfp))
>> -		goto retry;
>> -
>> +	ret = mas_empty_area_rev(&mas, min, max, size);
>> +	if (!ret)
>> +		ret = mas_store_gfp(&mas, entry, gfp);
>>   	mtree_unlock(mt);
>> +	if (!ret)
>> +		*startp = mas.index;
>>   	return ret;
>>   }
>>   EXPORT_SYMBOL(mtree_alloc_rrange);
>> -- 
>> 2.20.1
>>