Commit e3a9d9fc authored by Oscar Salvador's avatar Oscar Salvador Committed by Linus Torvalds
Browse files

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/20210421102701.25051-7-osalvador@suse.de


Signed-off-by: default avatarOscar Salvador <osalvador@suse.de>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4a3e5de9

Documentation/admin-guide/kernel-parameters.txt

+17 −0
Original line number Diff line number Diff line
@@ -2801,6 +2801,23 @@ 
			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>

mm/Makefile

+4 −1
Original line number Diff line number Diff line
@@ -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

mm/memory_hotplug.c

+9 −1
Original line number Diff line number Diff line
@@ -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.