linux-kernel - Re: [PATCH] mm/slab_common: use helper function is_power_of

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Date:   Fri, 18 Feb 2022 09:15:10 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>, <penberg@...nel.org>,
        <rientjes@...gle.com>, <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] mm/slab_common: use helper function is_power_of_2()

On 2022/2/18 1:04, Vlastimil Babka wrote:
> On 2/17/22 11:44, Miaohe Lin wrote:
>> On 2022/2/17 17:23, Vlastimil Babka wrote:
>>> On 2/17/22 10:16, Miaohe Lin wrote:
>>>> Use helper function is_power_of_2() to check if KMALLOC_MIN_SIZE is power
>>>> of two. Minor readability improvement.
>>>>
>>>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>>>
>>> We can try, but in case some compiler will no longer able to perform the
>>> check at build-time (although is_power_of_2() looks sufficiently trivial
>>> too), we'll have to revert it.
>>
>> I see. I checked the compiler in my env but there might be some compilers can't
>> perform the check at build-time.
> 
> I'll add this to the slab tree and linux-next and we'll see if wider testing
> uncovers such compilers. Should be unlikely.

Many thanks! :)

> 
>> Many thanks for your reply.
>>
>>>
>>>> ---
>>>>  mm/slab_common.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/mm/slab_common.c b/mm/slab_common.c
>>>> index 23f2ab0713b7..6ee64d6208b3 100644
>>>> --- a/mm/slab_common.c
>>>> +++ b/mm/slab_common.c
>>>> @@ -807,7 +807,7 @@ void __init setup_kmalloc_cache_index_table(void)
>>>>  	unsigned int i;
>>>>  
>>>>  	BUILD_BUG_ON(KMALLOC_MIN_SIZE > 256 ||
>>>> -		(KMALLOC_MIN_SIZE & (KMALLOC_MIN_SIZE - 1)));
>>>> +		!is_power_of_2(KMALLOC_MIN_SIZE));
>>>>  
>>>>  	for (i = 8; i < KMALLOC_MIN_SIZE; i += 8) {
>>>>  		unsigned int elem = size_index_elem(i);
>>>
>>> .
>>>
>>
> 
> .
>