[PATCH 1/1] memblock cleanup: Remove unnecessary check in memblock_find_in_range_node()

[PATCH 1/1] memblock cleanup: Remove unnecessary check in memblock_find_in_range_node()

[Tang Chen]

In memblock_find_in_range_node(), it has the following check at line 117 and 118:

 113         for_each_free_mem_range_reverse(i, nid, &this_start, &this_end, NULL) {
 114                 this_start = clamp(this_start, start, end);
 115                 this_end = clamp(this_end, start, end);
 116
 117                 if (this_end < size)
 118                         continue;
 119
 120                 cand = round_down(this_end - size, align);
 121                 if (cand >= this_start)
 122                         return cand;
 123         }

Since it finds memory from higher memory downwards, if this_end < size,
we can break because the rest memory will all under size. It won't satisfy
us ang more.

Furthermore, we don't need to check "if (this_end < size)" actually. Without
this confusing check, we only waste some loops. So this patch removes the
check.

Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
---
 mm/memblock.c |    3 ---
 1 files changed, 0 insertions(+), 3 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index a847bfe..e0c626e 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -114,9 +114,6 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start,
 		this_start = clamp(this_start, start, end);
 		this_end = clamp(this_end, start, end);
 
-		if (this_end < size)
-			continue;
-
 		cand = round_down(this_end - size, align);
 		if (cand >= this_start)
 			return cand;
-- 
1.7.1

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Re: [PATCH 1/1] memblock cleanup: Remove unnecessary check in memblock_find_in_range_node()

[Tejun Heo]

Hello, Tang.

On Thu, Aug 15, 2013 at 11:23:19AM +0800, Tang Chen wrote:
> Furthermore, we don't need to check "if (this_end < size)" actually. Without
> this confusing check, we only waste some loops. So this patch removes the
> check.
> 
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
> ---
>  mm/memblock.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index a847bfe..e0c626e 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -114,9 +114,6 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start,
>  		this_start = clamp(this_start, start, end);
>  		this_end = clamp(this_end, start, end);
>  
> -		if (this_end < size)
> -			continue;
> -
>  		cand = round_down(this_end - size, align);
>  		if (cand >= this_start)
>  			return cand;

Hmmm... maybe I'm missing something but are you sure?  "this_end -
size" can underflow and "cand >= this_start" will be true incorrectly.

Thanks.

-- 
tejun

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Re: [PATCH 1/1] memblock cleanup: Remove unnecessary check in memblock_find_in_range_node()

[Tang Chen]

On 08/15/2013 11:27 AM, Tejun Heo wrote:
> Hello, Tang.
>
> On Thu, Aug 15, 2013 at 11:23:19AM +0800, Tang Chen wrote:
>> Furthermore, we don't need to check "if (this_end<  size)" actually. Without
>> this confusing check, we only waste some loops. So this patch removes the
>> check.
>>
>> Signed-off-by: Tang Chen<tangchen@cn.fujitsu.com>
>> ---
>>   mm/memblock.c |    3 ---
>>   1 files changed, 0 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index a847bfe..e0c626e 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -114,9 +114,6 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start,
>>   		this_start = clamp(this_start, start, end);
>>   		this_end = clamp(this_end, start, end);
>>
>> -		if (this_end<  size)
>> -			continue;
>> -
>>   		cand = round_down(this_end - size, align);
>>   		if (cand>= this_start)
>>   			return cand;
>
> Hmmm... maybe I'm missing something but are you sure?  "this_end -
> size" can underflow and "cand>= this_start" will be true incorrectly.
>

Oh, you are right... Please ignore this. I didn't read it carefully.

Thanks.

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