[025/192] mm: sparsemem: use huge PMD mapping for vmemmap pages

Commit Message

Andrew Morton July 1, 2021, 1:48 a.m. UTC

From: Muchun Song <[e-mail]>
Subject: 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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Muchun Song <[e-mail]>
Reviewed-by: Mike Kravetz <[e-mail]>
Cc: Chen Huang <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Xiongchun Duan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 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(-)

Patch

--- a/arch/x86/mm/init_64.c~mm-sparsemem-use-huge-pmd-mapping-for-vmemmap-pages
+++ a/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
 	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(unsign
 	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(unsign
 		}
 		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))
--- a/Documentation/admin-guide/kernel-parameters.txt~mm-sparsemem-use-huge-pmd-mapping-for-vmemmap-pages
+++ a/Documentation/admin-guide/kernel-parameters.txt
@@ -1572,13 +1572,6 @@ 
 			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
--- a/include/linux/hugetlb.h~mm-sparsemem-use-huge-pmd-mapping-for-vmemmap-pages
+++ a/include/linux/hugetlb.h
@@ -895,20 +895,6 @@  static inline void huge_ptep_modify_prot
 }
 #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 {};
 
@@ -1063,13 +1049,14 @@  static inline void set_huge_swap_pte_at(
 					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)
 {
--- a/mm/memory_hotplug.c~mm-sparsemem-use-huge-pmd-mapping-for-vmemmap-pages
+++ a/mm/memory_hotplug.c
@@ -1056,7 +1056,7 @@  bool mhp_supports_memmap_on_memory(unsig
 	 *       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) &&