Message-Id: <20201217130758.11565-3-osalvador@suse.de>
Date:   Thu, 17 Dec 2020 14:07:55 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     akpm@...ux-foundation.org
Cc:     david@...hat.com, mhocko@...nel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, vbabka@...e.cz, pasha.tatashin@...een.com,
        Oscar Salvador <osalvador@...e.de>
Subject: [PATCH 2/5] mm,memory_hotplug: Allocate memmap from the added memory range

Physical memory hotadd has to allocate a memmap (struct page array) for
the newly added memory section. Currently, alloc_pages_node() is used
for those allocations.

This has some disadvantages:
 a) an existing memory is consumed for that purpose
    (eg: ~2MB per 128MB memory section on x86_64)
 b) if the whole node is movable then we have off-node struct pages
    which has performance drawbacks.
 c) It might be there are no PMD_ALIGNED chunks so memmap array gets
    populated with base pages.

This can be improved when CONFIG_SPARSEMEM_VMEMMAP is enabled.

Vmemap page tables can map arbitrary memory.
That means that we can simply use the beginning of each memory section and
map struct pages there.
struct pages which back the allocated space then just need to be treated
carefully.

Implementation wise we will reuse vmem_altmap infrastructure to override
the default allocator used by __populate_section_memmap.
Part of the implementation also relies on memory_block structure gaining
a new field which specifies the number of vmemmap_pages at the beginning.
This comes in handy as in {online,offline}_pages, all the isolation and
migration is being done on (buddy_start_pfn, end_pfn] range,
being buddy_start_pfn = start_pfn + nr_vmemmap_pages.

In this way, we have:

(start_pfn, buddy_start_pfn - 1] = Initialized and PageReserved
(buddy_start_pfn, end_pfn]       = Initialized and sent to buddy

Hot-remove:

 We need to be careful when removing memory, as adding and
 removing memory needs to be done with the same granularity.
 To check that this assumption is not violated, we check the
 memory range we want to remove and if a) any memory block has
 vmemmap pages and b) the range spans more than a single memory
 block, we scream out loud and refuse to proceed.

 If all is good and the range was using memmap on memory (aka vmemmap pages),
 we construct an altmap structure so free_hugepage_table does the right
 thing and calls vmem_altmap_free instead of free_pagetable.

Signed-off-by: Oscar Salvador <osalvador@...e.de>
---
 drivers/base/memory.c          |  20 +++--
 include/linux/memory.h         |   8 +-
 include/linux/memory_hotplug.h |  21 ++++-
 include/linux/memremap.h       |   2 +-
 include/linux/mmzone.h         |   5 ++
 mm/memory_hotplug.c            | 138 ++++++++++++++++++++++++++++-----
 mm/page_alloc.c                |   4 +-
 7 files changed, 163 insertions(+), 35 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index eef4ffb6122c..7219e805dcaa 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -175,7 +175,7 @@ int memory_notify(unsigned long val, void *v)
  */
 static int
 memory_block_action(unsigned long start_section_nr, unsigned long action,
-		    int online_type, int nid)
+		    int online_type, int nid, unsigned long nr_vmemmap_pages)
 {
 	unsigned long start_pfn;
 	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
@@ -185,10 +185,11 @@ memory_block_action(unsigned long start_section_nr, unsigned long action,
 
 	switch (action) {
 	case MEM_ONLINE:
-		ret = online_pages(start_pfn, nr_pages, online_type, nid);
+		ret = online_pages(start_pfn, nr_pages, nr_vmemmap_pages,
+				   online_type, nid);
 		break;
 	case MEM_OFFLINE:
-		ret = offline_pages(start_pfn, nr_pages);
+		ret = offline_pages(start_pfn, nr_pages, nr_vmemmap_pages);
 		break;
 	default:
 		WARN(1, KERN_WARNING "%s(%ld, %ld) unknown action: "
@@ -211,7 +212,7 @@ static int memory_block_change_state(struct memory_block *mem,
 		mem->state = MEM_GOING_OFFLINE;
 
 	ret = memory_block_action(mem->start_section_nr, to_state,
-				  mem->online_type, mem->nid);
+				  mem->online_type, mem->nid, mem->nr_vmemmap_pages);
 
 	mem->state = ret ? from_state_req : to_state;
 
@@ -571,7 +572,8 @@ int register_memory(struct memory_block *memory)
 	return ret;
 }
 
-static int init_memory_block(unsigned long block_id, unsigned long state)
+static int init_memory_block(unsigned long block_id, unsigned long state,
+			     unsigned long nr_vmemmap_pages)
 {
 	struct memory_block *mem;
 	unsigned long start_pfn;
@@ -591,6 +593,7 @@ static int init_memory_block(unsigned long block_id, unsigned long state)
 	start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	mem->phys_device = arch_get_memory_phys_device(start_pfn);
 	mem->nid = NUMA_NO_NODE;
+	mem->nr_vmemmap_pages = nr_vmemmap_pages;
 
 	ret = register_memory(mem);
 
@@ -610,7 +613,7 @@ static int add_memory_block(unsigned long base_section_nr)
 	if (section_count == 0)
 		return 0;
 	return init_memory_block(memory_block_id(base_section_nr),
-				 MEM_ONLINE);
+				 MEM_ONLINE, 0);
 }
 
 static void unregister_memory(struct memory_block *memory)
@@ -632,7 +635,8 @@ static void unregister_memory(struct memory_block *memory)
  *
  * Called under device_hotplug_lock.
  */
-int create_memory_block_devices(unsigned long start, unsigned long size)
+int create_memory_block_devices(unsigned long start, unsigned long size,
+				unsigned long vmemmap_pages)
 {
 	const unsigned long start_block_id = pfn_to_block_id(PFN_DOWN(start));
 	unsigned long end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
@@ -645,7 +649,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size)
 		return -EINVAL;
 
 	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
-		ret = init_memory_block(block_id, MEM_OFFLINE);
+		ret = init_memory_block(block_id, MEM_OFFLINE, vmemmap_pages);
 		if (ret)
 			break;
 	}
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 439a89e758d8..f09d60ef8ad9 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -30,6 +30,11 @@ struct memory_block {
 	int phys_device;		/* to which fru does this belong? */
 	struct device dev;
 	int nid;			/* NID for this memory block */
+	unsigned long nr_vmemmap_pages;	/*
+					 * Number of vmemmap pages. These pages
+					 * lay at the beginning of the memory
+					 * block.
+					 */
 };
 
 int arch_get_memory_phys_device(unsigned long start_pfn);
@@ -81,7 +86,8 @@ static inline int memory_notify(unsigned long val, void *v)
 #else
 extern int register_memory_notifier(struct notifier_block *nb);
 extern void unregister_memory_notifier(struct notifier_block *nb);
-int create_memory_block_devices(unsigned long start, unsigned long size);
+int create_memory_block_devices(unsigned long start, unsigned long size,
+				unsigned long vmemmap_pages);
 void remove_memory_block_devices(unsigned long start, unsigned long size);
 extern void memory_dev_init(void);
 extern int memory_notify(unsigned long val, void *v);
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 15acce5ab106..67ea4a0b25bd 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -70,6 +70,14 @@ typedef int __bitwise mhp_t;
  */
 #define MEMHP_MERGE_RESOURCE	((__force mhp_t)BIT(0))
 
+/*
+ * We want memmap (struct page array) to be self contained.
+ * To do so, we will use the beginning of the hot-added range to build
+ * the page tables for the memmap array that describes the entire range.
+ * Only selected architectures support it with SPARSE_VMEMMAP.
+ */
+#define MHP_MEMMAP_ON_MEMORY   ((__force mhp_t)BIT(1))
+
 /*
  * Extended parameters for memory hotplug:
  * altmap: alternative allocator for memmap array (optional)
@@ -113,11 +121,13 @@ extern int zone_grow_waitqueues(struct zone *zone, unsigned long nr_pages);
 extern int add_one_highpage(struct page *page, int pfn, int bad_ppro);
 /* VM interface that may be used by firmware interface */
 extern int online_pages(unsigned long pfn, unsigned long nr_pages,
-			int online_type, int nid);
+			unsigned long nr_vmemmap_pages, int online_type,
+			int nid);
 extern struct zone *test_pages_in_a_zone(unsigned long start_pfn,
 					 unsigned long end_pfn);
 extern void __offline_isolated_pages(unsigned long start_pfn,
-				     unsigned long end_pfn);
+				     unsigned long end_pfn,
+				     unsigned long buddy_start_pfn);
 
 typedef void (*online_page_callback_t)(struct page *page, unsigned int order);
 
@@ -312,7 +322,8 @@ static inline void pgdat_resize_init(struct pglist_data *pgdat) {}
 #ifdef CONFIG_MEMORY_HOTREMOVE
 
 extern void try_offline_node(int nid);
-extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
+extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
+			 unsigned long nr_vmemmap_pages);
 extern int remove_memory(int nid, u64 start, u64 size);
 extern void __remove_memory(int nid, u64 start, u64 size);
 extern int offline_and_remove_memory(int nid, u64 start, u64 size);
@@ -320,7 +331,8 @@ extern int offline_and_remove_memory(int nid, u64 start, u64 size);
 #else
 static inline void try_offline_node(int nid) {}
 
-static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
+static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
+				unsigned long nr_vmemmap_pages)
 {
 	return -EINVAL;
 }
@@ -364,6 +376,7 @@ extern struct zone *zone_for_pfn_range(int online_type, int nid, unsigned start_
 extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
 				      struct mhp_params *params);
 void arch_remove_linear_mapping(u64 start, u64 size);
+extern bool mhp_supports_memmap_on_memory(unsigned long size);
 #endif /* CONFIG_MEMORY_HOTPLUG */
 
 #endif /* __LINUX_MEMORY_HOTPLUG_H */
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 86c6c368ce9b..3de5d482ac1a 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -17,7 +17,7 @@ struct device;
  * @alloc: track pages consumed, private to vmemmap_populate()
  */
 struct vmem_altmap {
-	const unsigned long base_pfn;
+	unsigned long base_pfn;
 	const unsigned long end_pfn;
 	const unsigned long reserve;
 	unsigned long free;
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b593316bff3d..d16b4411e422 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -407,6 +407,11 @@ enum zone_type {
 	 *    techniques might use alloc_contig_range() to hide previously
 	 *    exposed pages from the buddy again (e.g., to implement some sort
 	 *    of memory unplug in virtio-mem).
+	 * 6. Memory-hotplug: when using memmap_on_memory and onlining the memory
+	 *    to the MOVABLE zone, the vmemmap pages are also placed in such
+	 *    zone. Such pages cannot be really moved around as they are
+	 *    self-stored in the range, but they are treated as movable when
+	 *    the range that they describe is about to be offlined.
 	 *
 	 * In general, no unmovable allocations that degrade memory offlining
 	 * should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range())
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index a8cef4955907..9371e7d3f583 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -42,6 +42,8 @@
 #include "internal.h"
 #include "shuffle.h"
 
+static bool memmap_on_memory_enabled;
+
 /*
  * online_page_callback contains pointer to current page onlining function.
  * Initially it is generic_online_page(). If it is required it could be
@@ -606,10 +608,23 @@ void generic_online_page(struct page *page, unsigned int order)
 }
 EXPORT_SYMBOL_GPL(generic_online_page);
 
-static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages)
+static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
+			       unsigned long buddy_start_pfn)
 {
 	const unsigned long end_pfn = start_pfn + nr_pages;
-	unsigned long pfn;
+	unsigned long pfn = buddy_start_pfn;
+	unsigned int order = MAX_ORDER - 1;
+
+	/*
+	 * When using memmap_on_memory, the range might be unaligned as the
+	 * first pfns are used for vmemmap pages. Align it in case we need to.
+	 */
+	if (pfn & ((1 << order) - 1)) {
+		while (pfn & ((1 << order) - 1))
+			order--;
+		(*online_page_callback)(pfn_to_page(pfn), order);
+		pfn += 1 << order;
+	}
 
 	/*
 	 * Online the pages in MAX_ORDER - 1 aligned chunks. The callback might
@@ -617,7 +632,7 @@ static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages)
 	 * later). We account all pages as being online and belonging to this
 	 * zone ("present").
 	 */
-	for (pfn = start_pfn; pfn < end_pfn; pfn += MAX_ORDER_NR_PAGES)
+	for (; pfn < end_pfn; pfn += MAX_ORDER_NR_PAGES)
 		(*online_page_callback)(pfn_to_page(pfn), MAX_ORDER - 1);
 
 	/* mark all involved sections as online */
@@ -777,9 +792,9 @@ struct zone * zone_for_pfn_range(int online_type, int nid, unsigned start_pfn,
 }
 
 int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
-		       int online_type, int nid)
+		       unsigned long nr_vmemmap_pages, int online_type, int nid)
 {
-	unsigned long flags;
+	unsigned long flags, buddy_start_pfn, buddy_nr_pages;
 	struct zone *zone;
 	int need_zonelists_rebuild = 0;
 	int ret;
@@ -790,11 +805,18 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 			 !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
+	buddy_start_pfn = pfn + nr_vmemmap_pages;
+	buddy_nr_pages = nr_pages - nr_vmemmap_pages;
+
 	mem_hotplug_begin();
 
 	/* associate pfn range with the zone */
 	zone = zone_for_pfn_range(online_type, nid, pfn, nr_pages);
-	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_ISOLATE);
+	if (nr_vmemmap_pages)
+		move_pfn_range_to_zone(zone, pfn, nr_vmemmap_pages, NULL,
+				       MIGRATE_UNMOVABLE);
+	move_pfn_range_to_zone(zone, buddy_start_pfn, buddy_nr_pages, NULL,
+			       MIGRATE_ISOLATE);
 
 	arg.start_pfn = pfn;
 	arg.nr_pages = nr_pages;
@@ -810,7 +832,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 	 * onlining, such that undo_isolate_page_range() works correctly.
 	 */
 	spin_lock_irqsave(&zone->lock, flags);
-	zone->nr_isolate_pageblock += nr_pages / pageblock_nr_pages;
+	zone->nr_isolate_pageblock += buddy_nr_pages / pageblock_nr_pages;
 	spin_unlock_irqrestore(&zone->lock, flags);
 
 	/*
@@ -823,7 +845,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 		setup_zone_pageset(zone);
 	}
 
-	online_pages_range(pfn, nr_pages);
+	online_pages_range(pfn, nr_pages, buddy_start_pfn);
 	zone->present_pages += nr_pages;
 
 	pgdat_resize_lock(zone->zone_pgdat, &flags);
@@ -836,7 +858,9 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 	zone_pcp_update(zone);
 
 	/* Basic onlining is complete, allow allocation of onlined pages. */
-	undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
+	undo_isolate_page_range(buddy_start_pfn,
+				buddy_start_pfn + buddy_nr_pages,
+				MIGRATE_MOVABLE);
 
 	/*
 	 * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
@@ -1011,6 +1035,12 @@ static int online_memory_block(struct memory_block *mem, void *arg)
 	return device_online(&mem->dev);
 }
 
+bool mhp_supports_memmap_on_memory(unsigned long size)
+{
+	return memmap_on_memory_enabled &&
+	       size == memory_block_size_bytes();
+}
+
 /*
  * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
  * and online/offline operations (triggered e.g. by sysfs).
@@ -1020,6 +1050,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
 int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
 {
 	struct mhp_params params = { .pgprot = PAGE_KERNEL };
+	struct vmem_altmap mhp_altmap = {};
 	u64 start, size;
 	bool new_node = false;
 	int ret;
@@ -1046,13 +1077,32 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
 		goto error;
 	new_node = ret;
 
+	/*
+	 * Return -EINVAL if the caller specified MHP_MEMMAP_ON_MEMORY and we do
+	 * not support it.
+	 */
+	if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
+	    !mhp_supports_memmap_on_memory(size)) {
+		ret = -EINVAL;
+		goto error;
+	}
+
+	/*
+	 * Self hosted memmap array
+	 */
+	if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
+		mhp_altmap.free = size >> PAGE_SHIFT;
+		mhp_altmap.base_pfn = start >> PAGE_SHIFT;
+		params.altmap = &mhp_altmap;
+	}
+
 	/* call arch's memory hotadd */
 	ret = arch_add_memory(nid, start, size, &params);
 	if (ret < 0)
 		goto error;
 
 	/* create memory block devices after memory was added */
-	ret = create_memory_block_devices(start, size);
+	ret = create_memory_block_devices(start, size, mhp_altmap.alloc);
 	if (ret) {
 		arch_remove_memory(nid, start, size, NULL);
 		goto error;
@@ -1448,10 +1498,11 @@ static int count_system_ram_pages_cb(unsigned long start_pfn,
 	return 0;
 }
 
-int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
+int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
+			unsigned long nr_vmemmap_pages)
 {
 	const unsigned long end_pfn = start_pfn + nr_pages;
-	unsigned long pfn, system_ram_pages = 0;
+	unsigned long pfn, buddy_start_pfn, buddy_nr_pages, system_ram_pages = 0;
 	unsigned long flags;
 	struct zone *zone;
 	struct memory_notify arg;
@@ -1463,6 +1514,9 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 			 !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
+	buddy_start_pfn = start_pfn + nr_vmemmap_pages;
+	buddy_nr_pages = nr_pages - nr_vmemmap_pages;
+
 	mem_hotplug_begin();
 
 	/*
@@ -1498,7 +1552,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	zone_pcp_disable(zone);
 
 	/* set above range as isolated */
-	ret = start_isolate_page_range(start_pfn, end_pfn,
+	ret = start_isolate_page_range(buddy_start_pfn, end_pfn,
 				       MIGRATE_MOVABLE,
 				       MEMORY_OFFLINE | REPORT_FAILURE);
 	if (ret) {
@@ -1518,7 +1572,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	}
 
 	do {
-		pfn = start_pfn;
+		pfn = buddy_start_pfn;
 		do {
 			if (signal_pending(current)) {
 				ret = -EINTR;
@@ -1549,18 +1603,18 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 		 * offlining actually in order to make hugetlbfs's object
 		 * counting consistent.
 		 */
-		ret = dissolve_free_huge_pages(start_pfn, end_pfn);
+		ret = dissolve_free_huge_pages(buddy_start_pfn, end_pfn);
 		if (ret) {
 			reason = "failure to dissolve huge pages";
 			goto failed_removal_isolated;
 		}
 
-		ret = test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE);
+		ret = test_pages_isolated(buddy_start_pfn, end_pfn, MEMORY_OFFLINE);
 
 	} while (ret);
 
 	/* Mark all sections offline and remove free pages from the buddy. */
-	__offline_isolated_pages(start_pfn, end_pfn);
+	__offline_isolated_pages(start_pfn, end_pfn, buddy_start_pfn);
 	pr_info("Offlined Pages %ld\n", nr_pages);
 
 	/*
@@ -1569,13 +1623,13 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	 * of isolated pageblocks, memory onlining will properly revert this.
 	 */
 	spin_lock_irqsave(&zone->lock, flags);
-	zone->nr_isolate_pageblock -= nr_pages / pageblock_nr_pages;
+	zone->nr_isolate_pageblock -= buddy_nr_pages / pageblock_nr_pages;
 	spin_unlock_irqrestore(&zone->lock, flags);
 
 	zone_pcp_enable(zone);
 
 	/* removal success */
-	adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages);
+	adjust_managed_page_count(pfn_to_page(start_pfn), -buddy_nr_pages);
 	zone->present_pages -= nr_pages;
 
 	pgdat_resize_lock(zone->zone_pgdat, &flags);
@@ -1635,6 +1689,16 @@ static int check_memblock_offlined_cb(struct memory_block *mem, void *arg)
 	return 0;
 }
 
+static int get_memblock_vmemmap_pages_cb(struct memory_block *mem, void *arg)
+{
+	unsigned long *nr_vmemmap_pages = (unsigned long *)arg;
+	int ret = !mem->nr_vmemmap_pages;
+
+	if (!ret)
+		*nr_vmemmap_pages += mem->nr_vmemmap_pages;
+	return ret;
+}
+
 static int check_cpu_on_node(pg_data_t *pgdat)
 {
 	int cpu;
@@ -1709,6 +1773,9 @@ EXPORT_SYMBOL(try_offline_node);
 static int __ref try_remove_memory(int nid, u64 start, u64 size)
 {
 	int rc = 0;
+	struct vmem_altmap mhp_altmap = {};
+	struct vmem_altmap *altmap = NULL;
+	unsigned long nr_vmemmap_pages = 0;
 
 	BUG_ON(check_hotplug_memory_range(start, size));
 
@@ -1721,6 +1788,37 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
 	if (rc)
 		return rc;
 
+	/*
+	 * When using MHP_MEMMAP_ON_MEMORY, add_memory and remove_memory needs
+	 * to work with the same granularity.
+	 * Check that we are not violating that assumption.
+	 * The only way we have right now is to walk all the memory
+	 * blocks we are trying to remove and see if any has vmemmap pages.
+	 * We should not have any as memmap_on_memory only works with ranges
+	 * that spans a single memory block, so if we found any and size spans
+	 * more than a memory block, we know we have to scream.
+	 * We only need to check this if memmap_on_memory_enabled=true.
+	 */
+	if (memmap_on_memory_enabled) {
+		(void)walk_memory_blocks(start, size, &nr_vmemmap_pages,
+					 get_memblock_vmemmap_pages_cb);
+		if (nr_vmemmap_pages) {
+			if (size != memory_block_size_bytes()) {
+				pr_warn("Refuse to remove %#llx - %#llx, wrong granularity\n"
+					 start, start + size);
+				return -EINVAL;
+			}
+
+			/*
+			 * Let remove_pmd_table->free_hugepage_table
+			 * do the right thing if we used vmem_altmap
+			 * when hot-adding the range.
+			 */
+			mhp_altmap.alloc = nr_vmemmap_pages;
+			altmap = &mhp_altmap;
+		}
+	}
+
 	/* remove memmap entry */
 	firmware_map_remove(start, start + size, "System RAM");
 
@@ -1732,7 +1830,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
 
 	mem_hotplug_begin();
 
-	arch_remove_memory(nid, start, size, NULL);
+	arch_remove_memory(nid, start, size, altmap);
 
 	if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
 		memblock_free(start, size);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 774542e1483e..02bca3b880a4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8825,7 +8825,8 @@ void zone_pcp_reset(struct zone *zone)
  * All pages in the range must be in a single zone, must not contain holes,
  * must span full sections, and must be isolated before calling this function.
  */
-void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
+void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn,
+			      unsigned long buddy_start_pfn)
 {
 	unsigned long pfn = start_pfn;
 	struct page *page;
@@ -8836,6 +8837,7 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 	offline_mem_sections(pfn, end_pfn);
 	zone = page_zone(pfn_to_page(pfn));
 	spin_lock_irqsave(&zone->lock, flags);
+	pfn = buddy_start_pfn;
 	while (pfn < end_pfn) {
 		page = pfn_to_page(pfn);
 		/*
-- 
2.26.2

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