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

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

On 11/04/2018 11:09, Christophe LEROY wrote:
> 
> 
> Le 11/04/2018 A  11:03, Laurent Dufour a A(C)critA :
>>
>>
>> On 11/04/2018 10:58, Christophe LEROY wrote:
>>>
>>>
>>> Le 11/04/2018 A  10:03, Laurent Dufour a A(C)critA :
>>>> 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>
>>>> ---
>>>> A A  mm/memory.c | 19 ++++++++-----------
>>>> A A  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,
>>>> A A A  * PFNMAP mappings in order to support COWable mappings.
>>>> A A A  *
>>>> A A A  */
>>>> -#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
>>>> -# define HAVE_PTE_SPECIAL 1
>>>> -#else
>>>> -# define HAVE_PTE_SPECIAL 0
>>>> -#endif
>>>> A A  struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long
>>>> addr,
>>>> A A A A A A A A A A A A A A A A A A A  pte_t pte, bool with_public_device)
>>>> A A  {
>>>> A A A A A A  unsigned long pfn = pte_pfn(pte);
>>>> A A  -A A A  if (HAVE_PTE_SPECIAL) {
>>>> +A A A  if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
>>>> A A A A A A A A A A  if (likely(!pte_special(pte)))
>>>> A A A A A A A A A A A A A A  goto check_pfn;
>>>> A A A A A A A A A A  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,
>>>> A A A A A A A A A A  return NULL;
>>>> A A A A A A  }
>>>> A A  -A A A  /* !HAVE_PTE_SPECIAL case follows: */
>>>> +A A A  /* !CONFIG_ARCH_HAS_PTE_SPECIAL case follows: */
>>>> A A  A A A A A  if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
>>>> A A A A A A A A A A  if (vma->vm_flags & VM_MIXEDMAP) {
>>>> @@ -881,7 +876,8 @@ struct page *_vm_normal_page(struct vm_area_struct *vma,
>>>> unsigned long addr,
>>>> A A  A A A A A  if (is_zero_pfn(pfn))
>>>> A A A A A A A A A A  return NULL;
>>>> -check_pfn:
>>>> +
>>>> +check_pfn: __maybe_unused
>>>
>>> See below
>>>
>>>> A A A A A A  if (unlikely(pfn > highest_memmap_pfn)) {
>>>> A A A A A A A A A A  print_bad_pte(vma, addr, pte, NULL);
>>>> A A A A A A A A A A  return NULL;
>>>> @@ -891,7 +887,7 @@ struct page *_vm_normal_page(struct vm_area_struct *vma,
>>>> unsigned long addr,
>>>> A A A A A A A  * NOTE! We still have PageReserved() pages in the page tables.
>>>> A A A A A A A  * eg. VDSO mappings can cause them to exist.
>>>> A A A A A A A  */
>>>> -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 ?
>>
> 
> Most likely, unless the mm maintainer agrees to remove them by himself when
> applying your patch ?

That was my point.

Andrew, should I send a v4 or could you wipe the 2 __maybe_unsued when applying
the patch ?

Thanks,
Laurent.