From e3a9d9fcc3315993de2e9fcd7ea82fab84433815 Mon Sep 17 00:00:00 2001 From: Oscar Salvador Date: Tue, 4 May 2021 18:39:48 -0700 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@suse.de Signed-off-by: Oscar Salvador Reviewed-by: David Hildenbrand Acked-by: Michal Hocko Cc: Anshuman Khandual Cc: Pavel Tatashin Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/admin-guide/kernel-parameters.txt | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'Documentation') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 1c0a3cf6fcc9..d93fbc1c1917 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/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: default : 0 -- cgit v1.2.3