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Subject[RFC PATCH v3 4/4] mm,memory_hotplug: Add mhp_memmap_on_memory boot option
Date
Self stored memmap leads to a sparse memory situation which is unsuitable
for workloads that requires large contiguous memory chunks.

Make this an opt-in which needs to be explicitly enabled.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
mm/memory_hotplug.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 4b4708512f82..858d6161e915 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -42,6 +42,8 @@
#include "internal.h"
#include "shuffle.h"

+static bool memmap_on_memory_enabled __read_mostly = false;
+
/*
* online_page_callback contains pointer to current page onlining function.
* Initially it is generic_online_page(). If it is required it could be
@@ -1034,7 +1036,7 @@ bool __weak arch_support_memmap_on_memory(void)

bool mhp_supports_memmap_on_memory(unsigned long size)
{
- if (!arch_support_memmap_on_memory() ||
+ if (!memmap_on_memory_enabled || !arch_support_memmap_on_memory() ||
!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) ||
size > memory_block_size_bytes())
return false;
@@ -1422,6 +1424,13 @@ static int __init cmdline_parse_movable_node(char *p)
}
early_param("movable_node", cmdline_parse_movable_node);

+static int __init cmdline_parse_memmap_on_memory(char *p)
+{
+ memmap_on_memory_enabled = true;
+ return 0;
+}
+early_param("mhp_memmap_on_memory", cmdline_parse_memmap_on_memory);
+
/* check which state of node_states will be changed when offline memory */
static void node_states_check_changes_offline(unsigned long nr_pages,
struct zone *zone, struct memory_notify *arg)
--
2.26.2
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