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Subject[PATCH v3 5/5] mm,memory_hotplug: Allow userspace to enable/disable vmemmap
Date
It seems that we have some users out there that want to expose all
hotpluggable memory to userspace, so this implements a toggling mechanism
for those users who want to disable it.

By default, vmemmap pages mechanism is enabled.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
drivers/base/memory.c | 33 +++++++++++++++++++++++++++++++++
include/linux/memory_hotplug.h | 3 +++
mm/memory_hotplug.c | 7 +++++++
3 files changed, 43 insertions(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index d30d0f6c8ad0..5ec6b80de9dd 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -578,6 +578,35 @@ static DEVICE_ATTR_WO(soft_offline_page);
static DEVICE_ATTR_WO(hard_offline_page);
#endif

+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+static ssize_t vmemmap_hotplug_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ if (vmemmap_enabled)
+ return sprintf(buf, "enabled\n");
+ else
+ return sprintf(buf, "disabled\n");
+}
+
+static ssize_t vmemmap_hotplug_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ if (sysfs_streq(buf, "enable"))
+ vmemmap_enabled = true;
+ else if (sysfs_streq(buf, "disable"))
+ vmemmap_enabled = false;
+ else
+ return -EINVAL;
+
+ return count;
+}
+static DEVICE_ATTR_RW(vmemmap_hotplug);
+#endif
+
/*
* Note that phys_device is optional. It is here to allow for
* differentiation between which *physical* devices each
@@ -794,6 +823,10 @@ static struct attribute *memory_root_attrs[] = {
&dev_attr_hard_offline_page.attr,
#endif

+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+ &dev_attr_vmemmap_hotplug.attr,
+#endif
+
&dev_attr_block_size_bytes.attr,
&dev_attr_auto_online_blocks.attr,
NULL
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index e1e8abf22a80..03d227d13301 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -134,6 +134,9 @@ extern int arch_add_memory(int nid, u64 start, u64 size,
struct mhp_restrictions *restrictions);
extern u64 max_mem_size;

+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+extern bool vmemmap_enabled;
+#endif
extern bool memhp_auto_online;
/* If movable_node boot option specified */
extern bool movable_node_enabled;
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 09d41339cd11..5ffe5375b87c 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -68,6 +68,10 @@ void put_online_mems(void)

bool movable_node_enabled = false;

+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+bool vmemmap_enabled __read_mostly = true;
+#endif
+
#ifndef CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE
bool memhp_auto_online;
#else
@@ -1108,6 +1112,9 @@ static unsigned long mhp_check_flags(unsigned long flags)
if (!flags)
return 0;

+ if (!vmemmap_enabled)
+ return 0;
+
if (flags != MHP_MEMMAP_ON_MEMORY) {
WARN(1, "Wrong flags value (%lx). Ignoring flags.\n", flags);
return 0;
--
2.12.3
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