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

From: Christophe LEROY
Date: Wed Apr 11 2018 - 04:59:00 EST




Le 11/04/2018 Ã 10:03, Laurent Dufour a ÃcritÂ:
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;
/*