linux-kernel - [PATCH 4/5] mm: sparsemem: use huge PMD mapping for vmemmap pages

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Message-Id: <20210609121310.62229-5-songmuchun@bytedance.com>
Date:   Wed,  9 Jun 2021 20:13:09 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        osalvador@...e.de, mhocko@...e.com, song.bao.hua@...ilicon.com,
        david@...hat.com, chenhuang5@...wei.com, bodeddub@...zon.com,
        corbet@....net
Cc:     duanxiongchun@...edance.com, fam.zheng@...edance.com,
        zhengqi.arch@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH 4/5] mm: sparsemem: use huge PMD mapping for vmemmap pages

The preparation of splitting huge PMD mapping of vmemmap pages is ready,
so switch the mapping from PTE to PMD.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  7 -------
 arch/x86/mm/init_64.c                           |  8 ++------
 include/linux/hugetlb.h                         | 25 ++++++-------------------
 mm/memory_hotplug.c                             |  2 +-
 4 files changed, 9 insertions(+), 33 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index db1ef6739613..a01aadafee38 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1599,13 +1599,6 @@
 			enabled.
 			Allows heavy hugetlb users to free up some more
 			memory (6 * PAGE_SIZE for each 2MB hugetlb page).
-			This feauture is not free though. Large page
-			tables are not used to back vmemmap pages which
-			can lead to a performance degradation for some
-			workloads. Also there will be memory allocation
-			required when hugetlb pages are freed from the
-			pool which can lead to corner cases under heavy
-			memory pressure.
 			Format: { on | off (default) }
 
 			on:  enable the feature
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 9d9d18d0c2a1..65ea58527176 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -34,7 +34,6 @@
 #include <linux/gfp.h>
 #include <linux/kcore.h>
 #include <linux/bootmem_info.h>
-#include <linux/hugetlb.h>
 
 #include <asm/processor.h>
 #include <asm/bios_ebda.h>
@@ -1610,8 +1609,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 	VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
 	VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
 
-	if ((is_hugetlb_free_vmemmap_enabled()  && !altmap) ||
-	    end - start < PAGES_PER_SECTION * sizeof(struct page))
+	if (end - start < PAGES_PER_SECTION * sizeof(struct page))
 		err = vmemmap_populate_basepages(start, end, node, NULL);
 	else if (boot_cpu_has(X86_FEATURE_PSE))
 		err = vmemmap_populate_hugepages(start, end, node, altmap);
@@ -1639,8 +1637,6 @@ void register_page_bootmem_memmap(unsigned long section_nr,
 	pmd_t *pmd;
 	unsigned int nr_pmd_pages;
 	struct page *page;
-	bool base_mapping = !boot_cpu_has(X86_FEATURE_PSE) ||
-			    is_hugetlb_free_vmemmap_enabled();
 
 	for (; addr < end; addr = next) {
 		pte_t *pte = NULL;
@@ -1666,7 +1662,7 @@ void register_page_bootmem_memmap(unsigned long section_nr,
 		}
 		get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO);
 
-		if (base_mapping) {
+		if (!boot_cpu_has(X86_FEATURE_PSE)) {
 			next = (addr + PAGE_SIZE) & PAGE_MASK;
 			pmd = pmd_offset(pud, addr);
 			if (pmd_none(*pmd))
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index c27a299c4211..2b46e6494114 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -907,20 +907,6 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 }
 #endif
 
-#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
-extern bool hugetlb_free_vmemmap_enabled;
-
-static inline bool is_hugetlb_free_vmemmap_enabled(void)
-{
-	return hugetlb_free_vmemmap_enabled;
-}
-#else
-static inline bool is_hugetlb_free_vmemmap_enabled(void)
-{
-	return false;
-}
-#endif
-
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 
@@ -1080,13 +1066,14 @@ static inline void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr
 					pte_t *ptep, pte_t pte, unsigned long sz)
 {
 }
-
-static inline bool is_hugetlb_free_vmemmap_enabled(void)
-{
-	return false;
-}
 #endif	/* CONFIG_HUGETLB_PAGE */
 
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+extern bool hugetlb_free_vmemmap_enabled;
+#else
+#define hugetlb_free_vmemmap_enabled	false
+#endif
+
 static inline spinlock_t *huge_pte_lock(struct hstate *h,
 					struct mm_struct *mm, pte_t *pte)
 {
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index d96a3c7551c8..9d8a551c08d5 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1056,7 +1056,7 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
 	 *       populate a single PMD.
 	 */
 	return memmap_on_memory &&
-	       !is_hugetlb_free_vmemmap_enabled() &&
+	       !hugetlb_free_vmemmap_enabled &&
 	       IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
 	       size == memory_block_size_bytes() &&
 	       IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
-- 
2.11.0