Re: [Xen-devel] [PATCHv3 01/10] mm: memory hotplug with an existing resource

[Tang Chen]

On 08/14/2015 04:40 AM, Andrew Morton wrote:
> On Thu, 13 Aug 2015 11:21:43 +0100 David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>
> > On 30/07/15 18:03, David Vrabel wrote:
> > > Add add_memory_resource() to add memory using an existing "System RAM"
> > > resource.  This is useful if the memory region is being located by
> > > finding a free resource slot with allocate_resource().
> > >
> > > Xen guests will make use of this in their balloon driver to hotplug
> > > arbitrary amounts of memory in response to toolstack requests.
> > Ping?  This enables a useful feature for Xen guests.
> Looks OK to me.  I've cc'ed some memory_hotplug.c developers.  If
> they're OK with it, please add the patch to the (Xen?) tree which uses
> it.
>
>
>
>
> Add add_memory_resource() to add memory using an existing "System RAM"
> resource.  This is useful if the memory region is being located by
> finding a free resource slot with allocate_resource().
>
> Xen guests will make use of this in their balloon driver to hotplug
> arbitrary amounts of memory in response to toolstack requests.
>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>   include/linux/memory_hotplug.h |  2 ++
>   mm/memory_hotplug.c            | 28 +++++++++++++++++++++-------
>   2 files changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 6ffa0ac..c76d371 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -11,6 +11,7 @@ struct zone;
>   struct pglist_data;
>   struct mem_section;
>   struct memory_block;
> +struct resource;
>   
>   #ifdef CONFIG_MEMORY_HOTPLUG
>   
> @@ -266,6 +267,7 @@ static inline void remove_memory(int nid, u64 start, u64 size) {}
>   extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
>   		void *arg, int (*func)(struct memory_block *, void *));
>   extern int add_memory(int nid, u64 start, u64 size);
> +extern int add_memory_resource(int nid, struct resource *resource);
>   extern int zone_for_memory(int nid, u64 start, u64 size, int zone_default);
>   extern int arch_add_memory(int nid, u64 start, u64 size);
>   extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 003dbe4..169770a 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1224,23 +1224,21 @@ int zone_for_memory(int nid, u64 start, u64 size, int zone_default)
>   }
>   
>   /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
> -int __ref add_memory(int nid, u64 start, u64 size)
> +int __ref add_memory_resource(int nid, struct resource *res)
>   {
> +	u64 start, size;
>   	pg_data_t *pgdat = NULL;
>   	bool new_pgdat;
>   	bool new_node;
> -	struct resource *res;
>   	int ret;
>   
> +	start = res->start;
> +	size = resource_size(res);
> +
>   	ret = check_hotplug_memory_range(start, size);
>   	if (ret)
>   		return ret;
>   
> -	res = register_memory_resource(start, size);
> -	ret = -EEXIST;
> -	if (!res)
> -		return ret;
> -
>   	{	/* Stupid hack to suppress address-never-null warning */
>   		void *p = NODE_DATA(nid);
>   		new_pgdat = !p;
> @@ -1290,6 +1288,22 @@ out:
>   	mem_hotplug_done();
>   	return ret;
>   }
> +EXPORT_SYMBOL_GPL(add_memory_resource);
> +
> +int __ref add_memory(int nid, u64 start, u64 size)
> +{
> +	struct resource *res;
> +	int ret;
> +
> +	res = register_memory_resource(start, size);
> +	if (!res)
> +		return -EEXIST;
> +
> +	ret = add_memory_resource(nid, res);
> +	if (ret < 0)

Not a big deal, but I think  "if (ret)"  is enough.

The code looks good.

Reviewed-by: Tang Chen <tangchen@xxxxxxxxxxxxxx>

Thanks.

> +		release_memory_resource(res);
> +	return ret;
> +}
>   EXPORT_SYMBOL_GPL(add_memory);
>   
>   #ifdef CONFIG_MEMORY_HOTREMOVE

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