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

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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@xxxxxxxxxxxxxxxxxx>
---
  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.

Christophe


  	return pfn_to_page(pfn);
  }
@@ -904,7 +900,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
  	/*
  	 * There is no pmd_special() but there may be special pmds, e.g.
  	 * in a direct-access (dax) mapping, so let's just replicate the
-	 * !HAVE_PTE_SPECIAL case from vm_normal_page() here.
+	 * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here.
  	 */
  	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
  		if (vma->vm_flags & VM_MIXEDMAP) {
@@ -1933,7 +1929,8 @@ static int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
  	 * than insert_pfn).  If a zero_pfn were inserted into a VM_MIXEDMAP
  	 * without pte special, it would there be refcounted as a normal page.
  	 */
-	if (!HAVE_PTE_SPECIAL && !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
+	if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) &&
+	    !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
  		struct page *page;
/*

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