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Subject[PATCH v2 3/7] mm,memory_hotplug: Add kernel boot option to enable memmap_on_memory
Date
Self stored memmap leads to a sparse memory situation which is unsuitable
for workloads that requires large contiguous memory chunks, so make this
an opt-in which needs to be explicitly enabled.

To control this, let memory_hotplug have its own memory space, as suggested
by David, so we can add memory_hotplug.memmap_on_memory parameter.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
Documentation/admin-guide/kernel-parameters.txt | 14 +++++++++++++
mm/Makefile | 5 ++++-
mm/memory_hotplug.c | 26 ++++++++++++++++++++++++-
3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5adf1e57e932..696beb5f6c92 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2811,6 +2811,20 @@
seconds. Use this parameter to check at some
other rate. 0 disables periodic checking.

+ memory_hotplug.memmap_on_memory
+ [KNL,X86,ARM] Boolean flag to enable this feature.
+ Format: {on | off (default)}
+ When enabled, memory to build the pages tables for the
+ memmap array describing the hot-added range will be taken
+ from the range itself, so the memmap page tables will be
+ self-hosted.
+ Since only single memory device ranges are supported at
+ the moment, this option is disabled by default because
+ it might have an impact on workloads that needs large
+ contiguous memory chunks.
+ The state of the flag can be read in
+ /sys/module/memory_hotplug/parameters/memmap_on_memory.
+
memtest= [KNL,X86,ARM,PPC] Enable memtest
Format: <integer>
default : 0 <disable>
diff --git a/mm/Makefile b/mm/Makefile
index b2a564eec27f..9e284dba50ef 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -58,9 +58,13 @@ obj-y := filemap.o mempool.o oom_kill.o fadvise.o \
page-alloc-y := page_alloc.o
page-alloc-$(CONFIG_SHUFFLE_PAGE_ALLOCATOR) += shuffle.o

+# Give 'memory_hotplug' its own module-parameter namespace
+memory-hotplug-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
+
obj-y += page-alloc.o
obj-y += init-mm.o
obj-y += memblock.o
+obj-y += $(memory-hotplug-y)

ifdef CONFIG_MMU
obj-$(CONFIG_ADVISE_SYSCALLS) += madvise.o
@@ -83,7 +87,6 @@ obj-$(CONFIG_SLUB) += slub.o
obj-$(CONFIG_KASAN) += kasan/
obj-$(CONFIG_KFENCE) += kfence/
obj-$(CONFIG_FAILSLAB) += failslab.o
-obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
obj-$(CONFIG_MEMTEST) += memtest.o
obj-$(CONFIG_MIGRATION) += migrate.o
obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 9bcc460e8bfe..95695483a622 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -42,7 +42,31 @@
#include "internal.h"
#include "shuffle.h"

-static bool memmap_on_memory_enabled;
+/*
+ * memory_hotplug.memmap_on_memory parameter
+ */
+static bool memmap_on_memory_enabled __ro_after_init;
+
+static int memmap_on_memory_show(char *buffer, const struct kernel_param *kp)
+{
+ return sprintf(buffer, "%s\n",
+ memmap_on_memory_enabled ? "on" : "off");
+}
+
+static __meminit int memmap_on_memory_store(const char *val,
+ const struct kernel_param *kp)
+{
+ /*
+ * Fail silently in case we cannot enable it due to platform constraints.
+ * User can always check whether it is enabled or not via /sys/module.
+ */
+ if (!IS_ENABLED(CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE))
+ return 0;
+
+ return param_set_bool(val, kp);
+}
+module_param_call(memmap_on_memory, memmap_on_memory_store,
+ memmap_on_memory_show, &memmap_on_memory_enabled, 0400);

/*
* online_page_callback contains pointer to current page onlining function.
--
2.16.3
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