linux-kernel - [PATCH v2 1/8] mm: hugetlb_vmemmap: delete hugetlb_optimize_vmemmap

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Date:   Tue, 28 Jun 2022 17:22:28 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     mike.kravetz@...cle.com, david@...hat.com,
        akpm@...ux-foundation.org, corbet@....net
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, duanxiongchun@...edance.com,
        Muchun Song <songmuchun@...edance.com>,
        Oscar Salvador <osalvador@...e.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: [PATCH v2 1/8] mm: hugetlb_vmemmap: delete hugetlb_optimize_vmemmap_enabled()

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 cf5a501d985b).  So it is easy to
remove hugetlb_optimize_vmemmap_enabled().

Link: https://lore.kernel.org/all/c77c61c8-8a5a-87e8-db89-d04d8aaab4cc@oracle.com/ [1]
Signed-off-by: Muchun Song <songmuchun@...edance.com>
Reviewed-by: Oscar Salvador <osalvador@...e.de>
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Anshuman Khandual <anshuman.khandual@....com>
---
 arch/arm64/mm/flush.c      | 13 +++----------
 include/linux/page-flags.h | 14 ++------------
 2 files changed, 5 insertions(+), 22 deletions(-)

diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
index fc4f710e9820..5f9379b3c8c8 100644
--- a/arch/arm64/mm/flush.c
+++ b/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))
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index ea19528564d1..2455405ab82b 100644
--- a/include/linux/page-flags.h
+++ b/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)
-- 
2.11.0