Re: [PATCH v3 2/2] mm: remove odd HAVE_PTE_SPECIAL

[Laurent Dufour <ldufour@linux.vnet.ibm.com>]

On 11/04/2018 10:58, Christophe LEROY wrote:
> 
> 
> Le 11/04/2018 à 10:03, Laurent Dufour a écrit :
>> Remove the additional define HAVE_PTE_SPECIAL and rely directly on
>> CONFIG_ARCH_HAS_PTE_SPECIAL.
>>
>> There is no functional change introduced by this patch
>>
>> Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
>> ---
>>   mm/memory.c | 19 ++++++++-----------
>>   1 file changed, 8 insertions(+), 11 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 96910c625daa..7f7dc7b2a341 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -817,17 +817,12 @@ static void print_bad_pte(struct vm_area_struct *vma,
>> unsigned long addr,
>>    * PFNMAP mappings in order to support COWable mappings.
>>    *
>>    */
>> -#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
>> -# define HAVE_PTE_SPECIAL 1
>> -#else
>> -# define HAVE_PTE_SPECIAL 0
>> -#endif
>>   struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>>                    pte_t pte, bool with_public_device)
>>   {
>>       unsigned long pfn = pte_pfn(pte);
>>   -    if (HAVE_PTE_SPECIAL) {
>> +    if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
>>           if (likely(!pte_special(pte)))
>>               goto check_pfn;
>>           if (vma->vm_ops && vma->vm_ops->find_special_page)
>> @@ -862,7 +857,7 @@ struct page *_vm_normal_page(struct vm_area_struct *vma,
>> unsigned long addr,
>>           return NULL;
>>       }
>>   -    /* !HAVE_PTE_SPECIAL case follows: */
>> +    /* !CONFIG_ARCH_HAS_PTE_SPECIAL case follows: */
>>         if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
>>           if (vma->vm_flags & VM_MIXEDMAP) {
>> @@ -881,7 +876,8 @@ struct page *_vm_normal_page(struct vm_area_struct *vma,
>> unsigned long addr,
>>         if (is_zero_pfn(pfn))
>>           return NULL;
>> -check_pfn:
>> +
>> +check_pfn: __maybe_unused
> 
> See below
> 
>>       if (unlikely(pfn > highest_memmap_pfn)) {
>>           print_bad_pte(vma, addr, pte, NULL);
>>           return NULL;
>> @@ -891,7 +887,7 @@ struct page *_vm_normal_page(struct vm_area_struct *vma,
>> unsigned long addr,
>>        * NOTE! We still have PageReserved() pages in the page tables.
>>        * eg. VDSO mappings can cause them to exist.
>>        */
>> -out:
>> +out: __maybe_unused
> 
> Why do you need that change ?
> 
> There is no reason for the compiler to complain. It would complain if the goto
> was within a #ifdef, but all the purpose of using IS_ENABLED() is to allow the
> compiler to properly handle all possible cases. That's all the force of
> IS_ENABLED() compared to ifdefs, and that the reason why they are plebicited,
> ref Linux Codying style for a detailed explanation.

Fair enough.

Should I submit a v4 just to remove these so ugly __maybe_unused ?