From: Oscar Salvador <osalvador@xxxxxxx> 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/20210421102701.25051-7-osalvador@xxxxxxx Signed-off-by: Oscar Salvador <osalvador@xxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- 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 @@ -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> --- 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. _
