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SubjectRe: [PATCH v3 5/5] mm,memory_hotplug: Allow userspace to enable/disable vmemmap
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On 25.07.19 18:02, Oscar Salvador wrote:
> 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
>

-ENODOCUMENTATION :)

> +#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,

Don't like the name of that property, sorry.

> +#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;
>

Hmmm, I wonder if that should that rather be a per-memory device driver
thingy? E.g., a toggle for ACPI which will then not pass in
MHP_MEMMAP_ON_MEMORY.

--

Thanks,

David / dhildenb

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