mm/thp: rename TRANSPARENT_HUGEPAGE_NEVER_DAX to _UNSUPPORTED

TRANSPARENT_HUGEPAGE_NEVER_DAX has nothing to do with DAX.  It's set when
has_transparent_hugepage() returns false, checked in hugepage_vma_check()
and will disable THP completely if false.  Rename it to
TRANSPARENT_HUGEPAGE_UNSUPPORTED to reflect its real purpose.

[peterx@redhat.com: fix comment, per David]
  Link: https://lkml.kernel.org/r/ZBMzQW674oHQJV7F@x1n
Link: https://lkml.kernel.org/r/20230315171642.1244625-1-peterx@redhat.comSigned-off-by: Peter Xu <peterx@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/huge_mm.h

@@ -79,7 +79,7 @@ static inline vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn,
 }
 
 enum transparent_hugepage_flag {
-	TRANSPARENT_HUGEPAGE_NEVER_DAX,
+	TRANSPARENT_HUGEPAGE_UNSUPPORTED,
 	TRANSPARENT_HUGEPAGE_FLAG,
 	TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 	TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,

mm/huge_memory.c

@@ -88,7 +88,7 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
 	/*
 	 * If the hardware/firmware marked hugepage support disabled.
 	 */
-	if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_NEVER_DAX))
+	if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_UNSUPPORTED))
 		return false;
 
 	/* khugepaged doesn't collapse DAX vma, but page fault is fine. */
@@ -460,11 +460,7 @@ static int __init hugepage_init(void)
 	struct kobject *hugepage_kobj;
 
 	if (!has_transparent_hugepage()) {
-		/*
-		 * Hardware doesn't support hugepages, hence disable
-		 * DAX PMD support.
-		 */
-		transparent_hugepage_flags = 1 << TRANSPARENT_HUGEPAGE_NEVER_DAX;
+		transparent_hugepage_flags = 1 << TRANSPARENT_HUGEPAGE_UNSUPPORTED;
 		return -EINVAL;
 	}