linux-kernel - Re: [RFC PATCH] mm: memblock: fix wrong memmove size in memblock_merge

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Message-ID: <50EA2511.3070009@cn.fujitsu.com>
Date:	Mon, 07 Jan 2013 09:29:53 +0800
From:	Lin Feng <linfeng@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	akpm@...ux-foundation.org, mingo@...nel.org, yinghai@...nel.org,
	liwanp@...ux.vnet.ibm.com, benh@...nel.crashing.org,
	tangchen@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: memblock: fix wrong memmove size in memblock_merge_regions()



On 01/04/2013 10:56 PM, Tejun Heo wrote:
> On Fri, Jan 04, 2013 at 05:10:50PM +0800, Lin Feng wrote:
>> The memmove span covers from (next+1) to the end of the array, and the index
>> of next is (i+1), so the index of (next+1) is (i+2). So the size of remaining
>> array elements is (type->cnt - (i + 2)).
>>
>> PS. It seems that memblock_merge_regions() could be made some improvement:
>> we need't memmove the remaining array elements until we find a none-mergable
>> element, but now we memmove everytime we find a neighboring compatible region.
>> I'm not sure if the trial is worth though.
>>
>> Cc: Tejun Heo <tj@...nel.org>
>> Signed-off-by: Lin Feng <linfeng@...fujitsu.com>
>> ---
>>  mm/memblock.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 6259055..85ce056 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -314,7 +314,7 @@ static void __init_memblock memblock_merge_regions(struct memblock_type *type)
>>  		}
>>  
>>  		this->size += next->size;
>> -		memmove(next, next + 1, (type->cnt - (i + 1)) * sizeof(*next));
>> +		memmove(next, next + 1, (type->cnt - (i + 2)) * sizeof(*next));
> 
> Heh, that's confusing.  Nice catch.  Can you please also add a comment
> explaning the index so that it's less confusing for the future readers?
Hi Tejun,

Glad to. I will resend it soon.

thanks,
linfeng
> 
> Thanks.
> 
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