mm: hugetlb_vmemmap: delete hugetlb_optimize_vmemmap_enabled()

Patch series "Simplify hugetlb vmemmap and improve its readability", v2.

This series aims to simplify hugetlb vmemmap and improve its readability.


This patch (of 8):

The name hugetlb_optimize_vmemmap_enabled() a bit confusing as it tests
two conditions (enabled and pages in use).  Instead of coming up to an
appropriate name, we could just delete it.  There is already a discussion
about deleting it in thread [1].

There is only one user of hugetlb_optimize_vmemmap_enabled() outside of
hugetlb_vmemmap, that is flush_dcache_page() in arch/arm64/mm/flush.c. 
However, it does not need to call hugetlb_optimize_vmemmap_enabled() in
flush_dcache_page() since HugeTLB pages are always fully mapped and only
head page will be set PG_dcache_clean meaning only head page's flag may
need to be cleared (see commit cf5a501d).  So it is easy to remove
hugetlb_optimize_vmemmap_enabled().

Link: https://lore.kernel.org/all/c77c61c8-8a5a-87e8-db89-d04d8aaab4cc@oracle.com/ [1]
Link: https://lkml.kernel.org/r/20220628092235.91270-2-songmuchun@bytedance.comSigned-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/arm64/mm/flush.c

@@ -76,17 +76,10 @@ EXPORT_SYMBOL_GPL(__sync_icache_dcache);
 void flush_dcache_page(struct page *page)
 {
 	/*
-	 * Only the head page's flags of HugeTLB can be cleared since the tail
-	 * vmemmap pages associated with each HugeTLB page are mapped with
-	 * read-only when CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is enabled (more
-	 * details can refer to vmemmap_remap_pte()).  Although
-	 * __sync_icache_dcache() only set PG_dcache_clean flag on the head
-	 * page struct, there is more than one page struct with PG_dcache_clean
-	 * associated with the HugeTLB page since the head vmemmap page frame
-	 * is reused (more details can refer to the comments above
-	 * page_fixed_fake_head()).
+	 * HugeTLB pages are always fully mapped and only head page will be
+	 * set PG_dcache_clean (see comments in __sync_icache_dcache()).
 	 */
-	if (hugetlb_optimize_vmemmap_enabled() && PageHuge(page))
+	if (PageHuge(page))
 		page = compound_head(page);
 
 	if (test_bit(PG_dcache_clean, &page->flags))

include/linux/page-flags.h

@@ -208,12 +208,6 @@ enum pageflags {
 DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
 			 hugetlb_optimize_vmemmap_key);
 
-static __always_inline bool hugetlb_optimize_vmemmap_enabled(void)
-{
-	return static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
-				   &hugetlb_optimize_vmemmap_key);
-}
-
 /*
  * If the feature of optimizing vmemmap pages associated with each HugeTLB
  * page is enabled, the head vmemmap page frame is reused and all of the tail
@@ -232,7 +226,8 @@ static __always_inline bool hugetlb_optimize_vmemmap_enabled(void)
  */
 static __always_inline const struct page *page_fixed_fake_head(const struct page *page)
 {
-	if (!hugetlb_optimize_vmemmap_enabled())
+	if (!static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
+				 &hugetlb_optimize_vmemmap_key))
 		return page;
 
 	/*
@@ -260,11 +255,6 @@ static inline const struct page *page_fixed_fake_head(const struct page *page)
 {
 	return page;
 }
-
-static inline bool hugetlb_optimize_vmemmap_enabled(void)
-{
-	return false;
-}
 #endif
 
 static __always_inline int page_is_fake_head(struct page *page)