patches/old/mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot.patch

From: Frank van der Linden <fvdl@google.com>
Subject: mm/sparse: allow for alternate vmemmap section init at boot
Date: Fri, 28 Feb 2025 18:29:11 +0000

Add functions that are called just before the per-section memmap is
initialized and just before the memmap page structures are initialized. 
They are called sparse_vmemmap_init_nid_early and
sparse_vmemmap_init_nid_late, respectively.

This allows for mm subsystems to add calls to initialize memmap and page
structures in a specific way, if using SPARSEMEM_VMEMMAP.  Specifically,
hugetlb can pre-HVO bootmem allocated pages that way, so that no time and
resources are wasted on allocating vmemmap pages, only to free them later
(and possibly unnecessarily running the system out of memory in the
process).

Refactor some code and export a few convenience functions for external
use.

In sparse_init_nid, skip any sections that are already initialized, e.g. 
they have been initialized by sparse_vmemmap_init_nid_early already.

The hugetlb code to use these functions will be added in a later commit.

Export section_map_size, as any alternate memmap init code will want to
use it.

The internal config option to enable this is SPARSEMEM_VMEMMAP_PREINIT,
which is selected if an architecture-specific option,
ARCH_WANT_HUGETLB_VMEMMAP_PREINIT, is set.  In the future, if other
subsystems want to do preinit too, they can do it in a similar fashion.

The internal config option is there because a section flag is used, and
the number of flags available is architecture-dependent (see mmzone.h). 
Architecures can decide if there is room for the flag when enabling
options that select SPARSEMEM_VMEMMAP_PREINIT.

Fortunately, as of right now, all sparse vmemmap using architectures do
have room.

Link: https://lkml.kernel.org/r/20250228182928.2645936-11-fvdl@google.com
Signed-off-by: Frank van der Linden <fvdl@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin (Cruise) <roman.gushchin@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/Kconfig             |    1 
 include/linux/mm.h     |    1 
 include/linux/mmzone.h |   35 +++++++++++++++
 mm/Kconfig             |    6 ++
 mm/bootmem_info.c      |    4 +
 mm/mm_init.c           |    3 +
 mm/sparse-vmemmap.c    |   23 ++++++++++
 mm/sparse.c            |   87 +++++++++++++++++++++++++++++----------
 8 files changed, 138 insertions(+), 22 deletions(-)

--- a/fs/Kconfig~mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot
+++ a/fs/Kconfig
@@ -286,6 +286,7 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	def_bool HUGETLB_PAGE
 	depends on ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
 	depends on SPARSEMEM_VMEMMAP
+	select SPARSEMEM_VMEMMAP_PREINIT if ARCH_WANT_HUGETLB_VMEMMAP_PREINIT
 
 config HUGETLB_PMD_PAGE_TABLE_SHARING
 	def_bool HUGETLB_PAGE
--- a/include/linux/mm.h~mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot
+++ a/include/linux/mm.h
@@ -3928,6 +3928,7 @@ static inline void print_vma_addr(char *
 #endif
 
 void *sparse_buffer_alloc(unsigned long size);
+unsigned long section_map_size(void);
 struct page * __populate_section_memmap(unsigned long pfn,
 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
 		struct dev_pagemap *pgmap);
--- a/include/linux/mmzone.h~mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot
+++ a/include/linux/mmzone.h
@@ -1934,6 +1934,9 @@ enum {
 #ifdef CONFIG_ZONE_DEVICE
 	SECTION_TAINT_ZONE_DEVICE_BIT,
 #endif
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_PREINIT
+	SECTION_IS_VMEMMAP_PREINIT_BIT,
+#endif
 	SECTION_MAP_LAST_BIT,
 };
 
@@ -1944,6 +1947,9 @@ enum {
 #ifdef CONFIG_ZONE_DEVICE
 #define SECTION_TAINT_ZONE_DEVICE	BIT(SECTION_TAINT_ZONE_DEVICE_BIT)
 #endif
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_PREINIT
+#define SECTION_IS_VMEMMAP_PREINIT	BIT(SECTION_IS_VMEMMAP_PREINIT_BIT)
+#endif
 #define SECTION_MAP_MASK		(~(BIT(SECTION_MAP_LAST_BIT) - 1))
 #define SECTION_NID_SHIFT		SECTION_MAP_LAST_BIT
 
@@ -1998,6 +2004,30 @@ static inline int online_device_section(
 }
 #endif
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_PREINIT
+static inline int preinited_vmemmap_section(struct mem_section *section)
+{
+	return (section &&
+		(section->section_mem_map & SECTION_IS_VMEMMAP_PREINIT));
+}
+
+void sparse_vmemmap_init_nid_early(int nid);
+void sparse_vmemmap_init_nid_late(int nid);
+
+#else
+static inline int preinited_vmemmap_section(struct mem_section *section)
+{
+	return 0;
+}
+static inline void sparse_vmemmap_init_nid_early(int nid)
+{
+}
+
+static inline void sparse_vmemmap_init_nid_late(int nid)
+{
+}
+#endif
+
 static inline int online_section_nr(unsigned long nr)
 {
 	return online_section(__nr_to_section(nr));
@@ -2035,6 +2065,9 @@ static inline int pfn_section_valid(stru
 }
 #endif
 
+void sparse_init_early_section(int nid, struct page *map, unsigned long pnum,
+			       unsigned long flags);
+
 #ifndef CONFIG_HAVE_ARCH_PFN_VALID
 /**
  * pfn_valid - check if there is a valid memory map entry for a PFN
@@ -2116,6 +2149,8 @@ void sparse_init(void);
 #else
 #define sparse_init()	do {} while (0)
 #define sparse_index_init(_sec, _nid)  do {} while (0)
+#define sparse_vmemmap_init_nid_early(_nid, _use) do {} while (0)
+#define sparse_vmemmap_init_nid_late(_nid) do {} while (0)
 #define pfn_in_present_section pfn_valid
 #define subsection_map_init(_pfn, _nr_pages) do {} while (0)
 #endif /* CONFIG_SPARSEMEM */
--- a/mm/bootmem_info.c~mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot
+++ a/mm/bootmem_info.c
@@ -88,7 +88,9 @@ static void __init register_page_bootmem
 
 	memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
 
-	register_page_bootmem_memmap(section_nr, memmap, PAGES_PER_SECTION);
+	if (!preinited_vmemmap_section(ms))
+		register_page_bootmem_memmap(section_nr, memmap,
+				PAGES_PER_SECTION);
 
 	usage = ms->usage;
 	page = virt_to_page(usage);
--- a/mm/Kconfig~mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot
+++ a/mm/Kconfig
@@ -442,6 +442,9 @@ config SPARSEMEM_VMEMMAP
 	  SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
 	  pfn_to_page and page_to_pfn operations.  This is the most
 	  efficient option when sufficient kernel resources are available.
+
+config SPARSEMEM_VMEMMAP_PREINIT
+	bool
 #
 # Select this config option from the architecture Kconfig, if it is preferred
 # to enable the feature of HugeTLB/dev_dax vmemmap optimization.
@@ -452,6 +455,9 @@ config ARCH_WANT_OPTIMIZE_DAX_VMEMMAP
 config ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
 	bool
 
+config ARCH_WANT_HUGETLB_VMEMMAP_PREINIT
+	bool
+
 config HAVE_MEMBLOCK_PHYS_MAP
 	bool
 
--- a/mm/mm_init.c~mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot
+++ a/mm/mm_init.c
@@ -1862,6 +1862,9 @@ void __init free_area_init(unsigned long
 		}
 	}
 
+	for_each_node_state(nid, N_MEMORY)
+		sparse_vmemmap_init_nid_late(nid);
+
 	calc_nr_kernel_pages();
 	memmap_init();
 
--- a/mm/sparse.c~mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot
+++ a/mm/sparse.c
@@ -408,13 +408,13 @@ static void __init check_usemap_section_
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
-static unsigned long __init section_map_size(void)
+unsigned long __init section_map_size(void)
 {
 	return ALIGN(sizeof(struct page) * PAGES_PER_SECTION, PMD_SIZE);
 }
 
 #else
-static unsigned long __init section_map_size(void)
+unsigned long __init section_map_size(void)
 {
 	return PAGE_ALIGN(sizeof(struct page) * PAGES_PER_SECTION);
 }
@@ -495,6 +495,44 @@ void __weak __meminit vmemmap_populate_p
 {
 }
 
+static void *sparse_usagebuf __meminitdata;
+static void *sparse_usagebuf_end __meminitdata;
+
+/*
+ * Helper function that is used for generic section initialization, and
+ * can also be used by any hooks added above.
+ */
+void __init sparse_init_early_section(int nid, struct page *map,
+				      unsigned long pnum, unsigned long flags)
+{
+	BUG_ON(!sparse_usagebuf || sparse_usagebuf >= sparse_usagebuf_end);
+	check_usemap_section_nr(nid, sparse_usagebuf);
+	sparse_init_one_section(__nr_to_section(pnum), pnum, map,
+			sparse_usagebuf, SECTION_IS_EARLY | flags);
+	sparse_usagebuf = (void *)sparse_usagebuf + mem_section_usage_size();
+}
+
+static int __init sparse_usage_init(int nid, unsigned long map_count)
+{
+	unsigned long size;
+
+	size = mem_section_usage_size() * map_count;
+	sparse_usagebuf = sparse_early_usemaps_alloc_pgdat_section(
+				NODE_DATA(nid), size);
+	if (!sparse_usagebuf) {
+		sparse_usagebuf_end = NULL;
+		return -ENOMEM;
+	}
+
+	sparse_usagebuf_end = sparse_usagebuf + size;
+	return 0;
+}
+
+static void __init sparse_usage_fini(void)
+{
+	sparse_usagebuf = sparse_usagebuf_end = NULL;
+}
+
 /*
  * Initialize sparse on a specific node. The node spans [pnum_begin, pnum_end)
  * And number of present sections in this node is map_count.
@@ -503,47 +541,54 @@ static void __init sparse_init_nid(int n
 				   unsigned long pnum_end,
 				   unsigned long map_count)
 {
-	struct mem_section_usage *usage;
 	unsigned long pnum;
 	struct page *map;
+	struct mem_section *ms;
 
-	usage = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nid),
-			mem_section_usage_size() * map_count);
-	if (!usage) {
+	if (sparse_usage_init(nid, map_count)) {
 		pr_err("%s: node[%d] usemap allocation failed", __func__, nid);
 		goto failed;
 	}
+
 	sparse_buffer_init(map_count * section_map_size(), nid);
+
+	sparse_vmemmap_init_nid_early(nid);
+
 	for_each_present_section_nr(pnum_begin, pnum) {
 		unsigned long pfn = section_nr_to_pfn(pnum);
 
 		if (pnum >= pnum_end)
 			break;
 
-		map = __populate_section_memmap(pfn, PAGES_PER_SECTION,
-				nid, NULL, NULL);
-		if (!map) {
-			pr_err("%s: node[%d] memory map backing failed. Some memory will not be available.",
-			       __func__, nid);
-			pnum_begin = pnum;
-			sparse_buffer_fini();
-			goto failed;
+		ms = __nr_to_section(pnum);
+		if (!preinited_vmemmap_section(ms)) {
+			map = __populate_section_memmap(pfn, PAGES_PER_SECTION,
+					nid, NULL, NULL);
+			if (!map) {
+				pr_err("%s: node[%d] memory map backing failed. Some memory will not be available.",
+				       __func__, nid);
+				pnum_begin = pnum;
+				sparse_usage_fini();
+				sparse_buffer_fini();
+				goto failed;
+			}
+			sparse_init_early_section(nid, map, pnum, 0);
 		}
-		check_usemap_section_nr(nid, usage);
-		sparse_init_one_section(__nr_to_section(pnum), pnum, map, usage,
-				SECTION_IS_EARLY);
-		usage = (void *) usage + mem_section_usage_size();
 	}
+	sparse_usage_fini();
 	sparse_buffer_fini();
 	return;
 failed:
-	/* We failed to allocate, mark all the following pnums as not present */
+	/*
+	 * We failed to allocate, mark all the following pnums as not present,
+	 * except the ones already initialized earlier.
+	 */
 	for_each_present_section_nr(pnum_begin, pnum) {
-		struct mem_section *ms;
-
 		if (pnum >= pnum_end)
 			break;
 		ms = __nr_to_section(pnum);
+		if (!preinited_vmemmap_section(ms))
+			ms->section_mem_map = 0;
 		ms->section_mem_map = 0;
 	}
 }
--- a/mm/sparse-vmemmap.c~mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot
+++ a/mm/sparse-vmemmap.c
@@ -470,3 +470,26 @@ struct page * __meminit __populate_secti
 
 	return pfn_to_page(pfn);
 }
+
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_PREINIT
+/*
+ * This is called just before initializing sections for a NUMA node.
+ * Any special initialization that needs to be done before the
+ * generic initialization can be done from here. Sections that
+ * are initialized in hooks called from here will be skipped by
+ * the generic initialization.
+ */
+void __init sparse_vmemmap_init_nid_early(int nid)
+{
+}
+
+/*
+ * This is called just before the initialization of page structures
+ * through memmap_init. Zones are now initialized, so any work that
+ * needs to be done that needs zone information can be done from
+ * here.
+ */
+void __init sparse_vmemmap_init_nid_late(int nid)
+{
+}
+#endif
_