Re: [PATCH v3 5/5] mm,memory_hotplug: Allow userspace to enable/disable vmemmap

From: David Hildenbrand <david@redhat.com>
To: Oscar Salvador <osalvador@suse.de>, akpm@linux-foundation.org
Cc: dan.j.williams@intel.com, pasha.tatashin@soleen.com,
	mhocko@suse.com, anshuman.khandual@arm.com,
	Jonathan.Cameron@huawei.com, vbabka@suse.cz, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 5/5] mm,memory_hotplug: Allow userspace to enable/disable vmemmap
Date: Thu, 1 Aug 2019 17:07:27 +0200	[thread overview]
Message-ID: <3bb12bac-77a5-c53a-247b-6241c8381d30@redhat.com> (raw)
In-Reply-To: <20190725160207.19579-6-osalvador@suse.de>

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