mm: thp: remove debug_cow switch

Since commit 3917c80280 ("thp: change CoW semantics for
anon-THP"), the CoW page fault of THP has been rewritten, debug_cow is not
used anymore.  So, just remove it.

Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/1592270980-116062-1-git-send-email-yang.shi@linux.alibaba.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/huge_mm.h

@@ -181,13 +181,6 @@ static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
 #define transparent_hugepage_use_zero_page()				\
 	(transparent_hugepage_flags &					\
 	 (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG))
-#ifdef CONFIG_DEBUG_VM
-#define transparent_hugepage_debug_cow()				\
-	(transparent_hugepage_flags &					\
-	 (1<<TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG))
-#else /* CONFIG_DEBUG_VM */
-#define transparent_hugepage_debug_cow() 0
-#endif /* CONFIG_DEBUG_VM */
 
 extern unsigned long thp_get_unmapped_area(struct file *filp,
 		unsigned long addr, unsigned long len, unsigned long pgoff,

mm/huge_memory.c

@@ -303,24 +303,6 @@ static ssize_t hpage_pmd_size_show(struct kobject *kobj,
 static struct kobj_attribute hpage_pmd_size_attr =
 	__ATTR_RO(hpage_pmd_size);
 
-#ifdef CONFIG_DEBUG_VM
-static ssize_t debug_cow_show(struct kobject *kobj,
-				struct kobj_attribute *attr, char *buf)
-{
-	return single_hugepage_flag_show(kobj, attr, buf,
-				TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
-}
-static ssize_t debug_cow_store(struct kobject *kobj,
-			       struct kobj_attribute *attr,
-			       const char *buf, size_t count)
-{
-	return single_hugepage_flag_store(kobj, attr, buf, count,
-				 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
-}
-static struct kobj_attribute debug_cow_attr =
-	__ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
-#endif /* CONFIG_DEBUG_VM */
-
 static struct attribute *hugepage_attr[] = {
 	&enabled_attr.attr,
 	&defrag_attr.attr,
@@ -328,9 +310,6 @@ static struct attribute *hugepage_attr[] = {
 	&hpage_pmd_size_attr.attr,
 #ifdef CONFIG_SHMEM
 	&shmem_enabled_attr.attr,
-#endif
-#ifdef CONFIG_DEBUG_VM
-	&debug_cow_attr.attr,
 #endif
 	NULL,
 };