+ mmmemory_hotplug-add-kernel-boot-option-to-enable-memmap_on_memory.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: mm,memory_hotplug: add kernel boot option to enable memmap_on_memory
has been added to the -mm tree.  Its filename is
     mmmemory_hotplug-add-kernel-boot-option-to-enable-memmap_on_memory.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mmmemory_hotplug-add-kernel-boot-option-to-enable-memmap_on_memory.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mmmemory_hotplug-add-kernel-boot-option-to-enable-memmap_on_memory.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Oscar Salvador <osalvador@suse.de>
Subject: mm,memory_hotplug: add kernel boot option to enable memmap_on_memory

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.

Link: https://lkml.kernel.org/r/20210416112411.9826-7-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/admin-guide/kernel-parameters.txt |   17 ++++++++++++++
 mm/Makefile                                     |    5 +++-
 mm/memory_hotplug.c                             |   10 +++++++-
 3 files changed, 30 insertions(+), 2 deletions(-)

--- a/Documentation/admin-guide/kernel-parameters.txt~mmmemory_hotplug-add-kernel-boot-option-to-enable-memmap_on_memory
+++ a/Documentation/admin-guide/kernel-parameters.txt
@@ -2794,6 +2794,23 @@
 			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, 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.
+			This feature is disabled by default because it
+			has some implication on large (e.g. GB)
+			allocations in some configurations (e.g. small
+			memory blocks).
+			The state of the flag can be read in
+			/sys/module/memory_hotplug/parameters/memmap_on_memory.
+			Note that even when enabled, there are a few cases where
+			the feature is not effective.
+
 	memtest=	[KNL,X86,ARM,PPC] Enable memtest
 			Format: <integer>
 			default : 0 <disable>
--- a/mm/Makefile~mmmemory_hotplug-add-kernel-boot-option-to-enable-memmap_on_memory
+++ a/mm/Makefile
@@ -58,9 +58,13 @@ obj-y			:= filemap.o mempool.o oom_kill.
 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
--- a/mm/memory_hotplug.c~mmmemory_hotplug-add-kernel-boot-option-to-enable-memmap_on_memory
+++ a/mm/memory_hotplug.c
@@ -42,7 +42,15 @@
 #include "internal.h"
 #include "shuffle.h"
 
-static bool memmap_on_memory;
+
+/*
+ * memory_hotplug.memmap_on_memory parameter
+ */
+static bool memmap_on_memory __ro_after_init;
+#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
+module_param(memmap_on_memory, bool, 0444);
+MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
+#endif
 
 /*
  * online_page_callback contains pointer to current page onlining function.
_

Patches currently in -mm which might be from osalvador@suse.de are

x86-vmemmap-drop-handling-of-4k-unaligned-vmemmap-range.patch
x86-vmemmap-drop-handling-of-1gb-vmemmap-ranges.patch
x86-vmemmap-handle-unpopulated-sub-pmd-ranges.patch
x86-vmemmap-handle-unpopulated-sub-pmd-ranges-fix.patch
x86-vmemmap-optimize-for-consecutive-sections-in-partial-populated-pmds.patch
drivers-base-memory-introduce-memory_block_onlineoffline.patch
mmmemory_hotplug-relax-fully-spanned-sections-check.patch
mmmemory_hotplug-allocate-memmap-from-the-added-memory-range.patch
acpimemhotplug-enable-mhp_memmap_on_memory-when-supported.patch
mmmemory_hotplug-add-kernel-boot-option-to-enable-memmap_on_memory.patch
x86-kconfig-introduce-arch_mhp_memmap_on_memory_enable.patch
arm64-kconfig-introduce-arch_mhp_memmap_on_memory_enable.patch