[PATCH 2/2] mm: memory_hotplug: introduce SECTION_CANNOT_OPTIMIZE_VMEMMAP

[Muchun Song <songmuchun@bytedance.com>]

For now, the feature of hugetlb_free_vmemmap is not compatible with the
feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap
takes precedence over memory_hotplug.memmap_on_memory. However, someone
wants to make memory_hotplug.memmap_on_memory takes precedence over
hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
succeed memory hotplug in close-to-OOM situations.  So the decision
of making hugetlb_free_vmemmap take precedence is not wise and elegant.
The proper approach is to have hugetlb_vmemmap.c do the check whether
the section which the HugeTLB pages belong to can be optimized.  If
the section's vmemmap pages are allocated from the added memory block
itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap,
otherwise, do the optimization.  Then both kernel parameters are
compatible.  So this patch introduces SECTION_CANNOT_OPTIMIZE_VMEMMAP
to indicate whether the section could be optimized.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 22 +++++++++----------
 Documentation/admin-guide/sysctl/vm.rst         |  5 ++---
 include/linux/memory_hotplug.h                  |  9 --------
 include/linux/mmzone.h                          | 17 +++++++++++++++
 mm/hugetlb_vmemmap.c                            | 28 ++++++++++++++++++-------
 mm/memory_hotplug.c                             | 22 +++++++------------
 mm/sparse.c                                     |  8 +++++++
 7 files changed, 66 insertions(+), 45 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index c087f578d9d8..5359ffb04a84 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1730,9 +1730,11 @@
 			Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
 			the default is on.
 
-			This is not compatible with memory_hotplug.memmap_on_memory.
-			If both parameters are enabled, hugetlb_free_vmemmap takes
-			precedence over memory_hotplug.memmap_on_memory.
+			Note that the vmemmap pages may be allocated from the added
+			memory block itself when memory_hotplug.memmap_on_memory is
+			enabled, those vmemmap pages cannot be optimized even if this
+			feature is enabled.  Other vmemmap pages not allocated from
+			the added memory block itself do not be affected.
 
 	hung_task_panic=
 			[KNL] Should the hung task detector generate panics.
@@ -3077,10 +3079,12 @@
 			[KNL,X86,ARM] Boolean flag to enable this feature.
 			Format: {on | off (default)}
 			When enabled, runtime hotplugged memory will
-			allocate its internal metadata (struct pages)
-			from the hotadded memory which will allow to
-			hotadd a lot of memory without requiring
-			additional memory to do so.
+			allocate its internal metadata (struct pages,
+			those vmemmap pages cannot be optimized even
+			if hugetlb_free_vmemmap is enabled) from the
+			hotadded memory which will allow to hotadd a
+			lot of memory without requiring additional
+			memory to do so.
 			This feature is disabled by default because it
 			has some implication on large (e.g. GB)
 			allocations in some configurations (e.g. small
@@ -3090,10 +3094,6 @@
 			Note that even when enabled, there are a few cases where
 			the feature is not effective.
 
-			This is not compatible with hugetlb_free_vmemmap. If
-			both parameters are enabled, hugetlb_free_vmemmap takes
-			precedence over memory_hotplug.memmap_on_memory.
-
 	memtest=	[KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
 			Format: <integer>
 			default : 0 <disable>
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 5c9aa171a0d3..d7374a1e8ac9 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -565,9 +565,8 @@ See Documentation/admin-guide/mm/hugetlbpage.rst
 hugetlb_optimize_vmemmap
 ========================
 
-This knob is not available when memory_hotplug.memmap_on_memory (kernel parameter)
-is configured or the size of 'struct page' (a structure defined in
-include/linux/mm_types.h) is not power of two (an unusual system config could
+This knob is not available when the size of 'struct page' (a structure defined
+in include/linux/mm_types.h) is not power of two (an unusual system config could
 result in this).
 
 Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 20d7edf62a6a..e0b2209ab71c 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -351,13 +351,4 @@ void arch_remove_linear_mapping(u64 start, u64 size);
 extern bool mhp_supports_memmap_on_memory(unsigned long size);
 #endif /* CONFIG_MEMORY_HOTPLUG */
 
-#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
-bool mhp_memmap_on_memory(void);
-#else
-static inline bool mhp_memmap_on_memory(void)
-{
-	return false;
-}
-#endif
-
 #endif /* __LINUX_MEMORY_HOTPLUG_H */
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index e0b7618d7212..3f73f24f394c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1434,6 +1434,7 @@ extern size_t mem_section_usage_size(void);
 	MAPPER(IS_ONLINE)							\
 	MAPPER(IS_EARLY)							\
 	MAPPER(TAINT_ZONE_DEVICE, CONFIG_ZONE_DEVICE)				\
+	MAPPER(CANNOT_OPTIMIZE_VMEMMAP, CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP)	\
 	MAPPER(MAP_LAST_BIT)
 
 #define __SECTION_SHIFT_FLAG_MAPPER_0(x)
@@ -1471,6 +1472,22 @@ static inline struct page *__section_mem_map_addr(struct mem_section *section)
 	return (struct page *)map;
 }
 
+#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+static inline void section_mark_cannot_optimize_vmemmap(struct mem_section *ms)
+{
+	ms->section_mem_map |= SECTION_CANNOT_OPTIMIZE_VMEMMAP;
+}
+
+static inline int section_cannot_optimize_vmemmap(struct mem_section *ms)
+{
+	return (ms && (ms->section_mem_map & SECTION_CANNOT_OPTIMIZE_VMEMMAP));
+}
+#else
+static inline void section_mark_cannot_optimize_vmemmap(struct mem_section *ms)
+{
+}
+#endif
+
 static inline int present_section(struct mem_section *section)
 {
 	return (section && (section->section_mem_map & SECTION_MARKED_PRESENT));
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index fcd9f7872064..f12170520337 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -97,18 +97,32 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
 	return ret;
 }
 
+static unsigned int optimizable_vmemmap_pages(struct hstate *h,
+					      struct page *head)
+{
+	unsigned long pfn = page_to_pfn(head);
+	unsigned long end = pfn + pages_per_huge_page(h);
+
+	if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
+		return 0;
+
+	for (; pfn < end; pfn += PAGES_PER_SECTION) {
+		if (section_cannot_optimize_vmemmap(__pfn_to_section(pfn)))
+			return 0;
+	}
+
+	return hugetlb_optimize_vmemmap_pages(h);
+}
+
 void hugetlb_vmemmap_free(struct hstate *h, struct page *head)
 {
 	unsigned long vmemmap_addr = (unsigned long)head;
 	unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
 
-	vmemmap_pages = hugetlb_optimize_vmemmap_pages(h);
+	vmemmap_pages = optimizable_vmemmap_pages(h, head);
 	if (!vmemmap_pages)
 		return;
 
-	if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
-		return;
-
 	static_branch_inc(&hugetlb_optimize_vmemmap_key);
 
 	vmemmap_addr	+= RESERVE_VMEMMAP_SIZE;
@@ -199,10 +213,10 @@ static struct ctl_table hugetlb_vmemmap_sysctls[] = {
 static __init int hugetlb_vmemmap_sysctls_init(void)
 {
 	/*
-	 * If "memory_hotplug.memmap_on_memory" is enabled or "struct page"
-	 * crosses page boundaries, the vmemmap pages cannot be optimized.
+	 * If "struct page" crosses page boundaries, the vmemmap pages cannot
+	 * be optimized.
 	 */
-	if (!mhp_memmap_on_memory() && is_power_of_2(sizeof(struct page)))
+	if (is_power_of_2(sizeof(struct page)))
 		register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
 
 	return 0;
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 3b360eda933f..7309694c4dee 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -43,30 +43,22 @@
 #include "shuffle.h"
 
 #ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
-static int memmap_on_memory_set(const char *val, const struct kernel_param *kp)
-{
-	if (hugetlb_optimize_vmemmap_enabled())
-		return 0;
-	return param_set_bool(val, kp);
-}
-
-static const struct kernel_param_ops memmap_on_memory_ops = {
-	.flags	= KERNEL_PARAM_OPS_FL_NOARG,
-	.set	= memmap_on_memory_set,
-	.get	= param_get_bool,
-};
-
 /*
  * memory_hotplug.memmap_on_memory parameter
  */
 static bool memmap_on_memory __ro_after_init;
-module_param_cb(memmap_on_memory, &memmap_on_memory_ops, &memmap_on_memory, 0444);
+module_param(memmap_on_memory, bool, 0444);
 MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
 
-bool mhp_memmap_on_memory(void)
+static inline bool mhp_memmap_on_memory(void)
 {
 	return memmap_on_memory;
 }
+#else
+static inline bool mhp_memmap_on_memory(void)
+{
+	return false;
+}
 #endif
 
 enum {
diff --git a/mm/sparse.c b/mm/sparse.c
index cb3bfae64036..1f353bf9ea6b 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -913,6 +913,14 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
 	ms = __nr_to_section(section_nr);
 	set_section_nid(section_nr, nid);
 	__section_mark_present(ms, section_nr);
+	/*
+	 * Mark whole section as non-optimizable once there is a subsection
+	 * whose vmemmap pages are allocated from alternative allocator. The
+	 * early section is always optimizable since the early section's
+	 * vmemmap pages do not consider partially being populated.
+	 */
+	if (!early_section(ms) && altmap)
+		section_mark_cannot_optimize_vmemmap(ms);
 
 	/* Align memmap to section boundary in the subsection case */
 	if (section_nr_to_pfn(section_nr) != start_pfn)
-- 
2.11.0