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* + mm-memory_hotplug-export-mhp_supports_memmap_on_memory.patch added to mm-unstable branch
@ 2024-01-26  2:16 Andrew Morton
  0 siblings, 0 replies; only message in thread
From: Andrew Morton @ 2024-01-26  2:16 UTC (permalink / raw)
  To: mm-commits, ying.huang, willy, osalvador, nvdimm, mhocko,
	lizhijian, Jonathan.Cameron, gregkh, david, dave.jiang,
	dave.hansen, dan.j.williams, akpm, vishal.l.verma, akpm

The patch titled
     Subject: mm/memory_hotplug: export mhp_supports_memmap_on_memory()
has been added to the -mm mm-unstable branch.  Its filename is

This patch will shortly appear at

This patch will later appear in the mm-unstable branch at

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From: Vishal Verma <>
Subject: mm/memory_hotplug: export mhp_supports_memmap_on_memory()
Date: Wed, 24 Jan 2024 12:03:49 -0800

In preparation for adding sysfs ABI to toggle memmap_on_memory semantics
for drivers adding memory, export the mhp_supports_memmap_on_memory()
helper. This allows drivers to check if memmap_on_memory support is
available before trying to request it, and display an appropriate
message if it isn't available. As part of this, remove the size argument
to this - with recent updates to allow memmap_on_memory for larger
ranges, and the internal splitting of altmaps into respective memory
blocks, the size argument is meaningless.

Cc: Andrew Morton <>
Cc: David Hildenbrand <>
Cc: Michal Hocko <>
Cc: Oscar Salvador <>
Cc: Dan Williams <>
Cc: Dave Jiang <>
Cc: Dave Hansen <>
Cc: Huang Ying <>
Suggested-by: David Hildenbrand <>
Acked-by: David Hildenbrand <>
Signed-off-by: Vishal Verma <>
Cc: Greg Kroah-Hartman <>
Cc: Jonathan Cameron <>
Cc: Li Zhijian <>
Cc: Matthew Wilcox (Oracle) <>
Cc: <>
Signed-off-by: Andrew Morton <>

 include/linux/memory_hotplug.h |    6 ++++++
 mm/memory_hotplug.c            |   17 ++++++-----------
 2 files changed, 12 insertions(+), 11 deletions(-)

--- a/include/linux/memory_hotplug.h~mm-memory_hotplug-export-mhp_supports_memmap_on_memory
+++ a/include/linux/memory_hotplug.h
@@ -137,6 +137,7 @@ struct mhp_params {
 bool mhp_range_allowed(u64 start, u64 size, bool need_mapping);
 struct range mhp_get_pluggable_range(bool need_mapping);
+bool mhp_supports_memmap_on_memory(void);
  * Zone resizing functions
@@ -277,6 +278,11 @@ static inline bool movable_node_is_enabl
 	return false;
+static bool mhp_supports_memmap_on_memory(void)
+	return false;
 static inline void pgdat_kswapd_lock(pg_data_t *pgdat) {}
 static inline void pgdat_kswapd_unlock(pg_data_t *pgdat) {}
--- a/mm/memory_hotplug.c~mm-memory_hotplug-export-mhp_supports_memmap_on_memory
+++ a/mm/memory_hotplug.c
@@ -1337,7 +1337,7 @@ static inline bool arch_supports_memmap_
-static bool mhp_supports_memmap_on_memory(unsigned long size)
+bool mhp_supports_memmap_on_memory(void)
 	unsigned long vmemmap_size = memory_block_memmap_size();
 	unsigned long memmap_pages = memory_block_memmap_on_memory_pages();
@@ -1346,17 +1346,11 @@ static bool mhp_supports_memmap_on_memor
 	 * Besides having arch support and the feature enabled at runtime, we
 	 * need a few more assumptions to hold true:
-	 * a) We span a single memory block: memory onlining/offlinin;g happens
-	 *    in memory block granularity. We don't want the vmemmap of online
-	 *    memory blocks to reside on offline memory blocks. In the future,
-	 *    we might want to support variable-sized memory blocks to make the
-	 *    feature more versatile.
-	 *
-	 * b) The vmemmap pages span complete PMDs: We don't want vmemmap code
+	 * a) The vmemmap pages span complete PMDs: We don't want vmemmap code
 	 *    to populate memory from the altmap for unrelated parts (i.e.,
 	 *    other memory blocks)
-	 * c) The vmemmap pages (and thereby the pages that will be exposed to
+	 * b) The vmemmap pages (and thereby the pages that will be exposed to
 	 *    the buddy) have to cover full pageblocks: memory onlining/offlining
 	 *    code requires applicable ranges to be page-aligned, for example, to
 	 *    set the migratetypes properly.
@@ -1368,7 +1362,7 @@ static bool mhp_supports_memmap_on_memor
 	 *       altmap as an alternative source of memory, and we do not exactly
 	 *       populate a single PMD.
-	if (!mhp_memmap_on_memory() || size != memory_block_size_bytes())
+	if (!mhp_memmap_on_memory())
 		return false;
@@ -1391,6 +1385,7 @@ static bool mhp_supports_memmap_on_memor
 	return arch_supports_memmap_on_memory(vmemmap_size);
 static void __ref remove_memory_blocks_and_altmaps(u64 start, u64 size)
@@ -1526,7 +1521,7 @@ int __ref add_memory_resource(int nid, s
 	 * Self hosted memmap array
 	if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
-	    mhp_supports_memmap_on_memory(memory_block_size_bytes())) {
+	    mhp_supports_memmap_on_memory()) {
 		ret = create_altmaps_and_memory_blocks(nid, group, start, size, mhp_flags);
 		if (ret)
 			goto error;

Patches currently in -mm which might be from are


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2024-01-26  2:16 + mm-memory_hotplug-export-mhp_supports_memmap_on_memory.patch added to mm-unstable branch Andrew Morton

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