[PATCH v2 1/3] mm: vmalloc: Let user to control huge vmalloc default behavior

[Kefeng Wang]

Introduce HUGE_VMALLOC_DEFAULT_ENABLED and make it default y, this
let user to choose whether or not enable huge vmalloc mappings by
default.

Meanwhile, add new hugevmalloc=on/off parameter to enable or disable
this feature at boot time, nohugevmalloc is still supported and
equivalent to hugevmalloc=off.

Signed-off-by: Kefeng Wang <wangkefeng.wang at huawei.com>
---
 .../admin-guide/kernel-parameters.txt          | 12 ++++++++++++
 mm/Kconfig                                     |  8 ++++++++
 mm/vmalloc.c                                   | 18 +++++++++++++++++-
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a069d8fe2fee..7b2f900fd243 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1638,6 +1638,18 @@
 			If both parameters are enabled, hugetlb_free_vmemmap takes
 			precedence over memory_hotplug.memmap_on_memory.
 
+
+	hugevmalloc=	[PPC] Reguires CONFIG_HAVE_ARCH_HUGE_VMALLOC
+			Format: { on | off }
+			Default set by CONFIG_HUGE_VMALLOC_DEFAULT_ENABLED.
+
+			This parameter enables/disables kernel huge vmalloc
+			mappings at boot time.
+
+			on:  Enable the feature
+			off: Disable the feature
+			     Equivalent to: nohugevmalloc
+
 	hung_task_panic=
 			[KNL] Should the hung task detector generate panics.
 			Format: 0 | 1
diff --git a/mm/Kconfig b/mm/Kconfig
index a99bd499ef51..8d8a92f22905 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -262,6 +262,14 @@ config HUGETLB_PAGE_SIZE_VARIABLE
 	  HUGETLB_PAGE_ORDER when there are multiple HugeTLB page sizes available
 	  on a platform.
 
+config HUGE_VMALLOC_DEFAULT_ENABLED
+	bool "Enable huge vmalloc mappings by default"
+	default y
+	depends on HAVE_ARCH_HUGE_VMALLOC
+	help
+	  Enable huge vmalloc mappings by default, this value could be overridden
+	  by hugevmalloc=off|on.
+
 config CONTIG_ALLOC
 	def_bool (MEMORY_ISOLATION && COMPACTION) || CMA
 
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 9bf838817a47..0d0f8deb5639 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -60,7 +60,7 @@ static const unsigned int ioremap_max_page_shift = PAGE_SHIFT;
 #endif	/* CONFIG_HAVE_ARCH_HUGE_VMAP */
 
 #ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC
-static bool __ro_after_init vmap_allow_huge = true;
+static bool __ro_after_init vmap_allow_huge = IS_ENABLED(CONFIG_HUGE_VMALLOC_DEFAULT_ENABLED);
 
 static int __init set_nohugevmalloc(char *str)
 {
@@ -68,6 +68,22 @@ static int __init set_nohugevmalloc(char *str)
 	return 0;
 }
 early_param("nohugevmalloc", set_nohugevmalloc);
+
+static int __init set_hugevmalloc(char *str)
+{
+	if (!str)
+		return -EINVAL;
+
+	if (!strcmp(str, "on"))
+		vmap_allow_huge = true;
+	else if (!strcmp(str, "off"))
+		vmap_allow_huge = false;
+	else
+		return -EINVAL;
+
+	return 0;
+}
+early_param("hugevmalloc", set_hugevmalloc);
 #else /* CONFIG_HAVE_ARCH_HUGE_VMALLOC */
 static const bool vmap_allow_huge = false;
 #endif	/* CONFIG_HAVE_ARCH_HUGE_VMALLOC */
-- 
2.26.2