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

On 11/04/2018 11:09, Christophe LEROY wrote:

Le 11/04/2018 à 11:03, Laurent Dufour a écrit :

quoted

On 11/04/2018 10:58, Christophe LEROY wrote:

quoted

Le 11/04/2018 à 10:03, Laurent Dufour a écrit :

quoted

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 <redacted>
---
   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

quoted

       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 ?

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.