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

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Date:   Thu, 17 Feb 2022 18:04:01 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Miaohe Lin <linmiaohe@...wei.com>
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 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 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);
>> 
>> .
>> 
>