Subject: Re: [RFC v9 PATCH 05/21] memory-hotplug: check whether memory is present or not

From: Wen Congyang <[email-masked]>
Date: Tue, 11 Sep 2012 10:15:26 +0800

Hi, ishimatsu

At 09/05/2012 05:25 PM, [email-masked] Wrote:
> From: Yasuaki Ishimatsu <[email-masked]>
> 
> If system supports memory hot-remove, online_pages() may online removed pages.
> So online_pages() need to check whether onlining pages are present or not.

Because we use memory_block_change_state() to hotremoving memory, I think
this patch can be removed. What do you think?

Thanks
Wen Congyang

> 
> CC: David Rientjes <[email-masked]>
> CC: Jiang Liu <[email-masked]>
> CC: Len Brown <[email-masked]>
> CC: Benjamin Herrenschmidt <[email-masked]>
> CC: Paul Mackerras <[email-masked]>
> CC: Christoph Lameter <[email-masked]>
> Cc: Minchan Kim <[email-masked]>
> CC: Andrew Morton <[email-masked]>
> CC: KOSAKI Motohiro <[email-masked]>
> CC: Wen Congyang <[email-masked]>
> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
> ---
>  include/linux/mmzone.h |   19 +++++++++++++++++++
>  mm/memory_hotplug.c    |   13 +++++++++++++
>  2 files changed, 32 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 2daa54f..ac3ae30 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1180,6 +1180,25 @@ void sparse_init(void);
>  #define sparse_index_init(_sec, _nid)  do {} while (0)
>  #endif /* CONFIG_SPARSEMEM */
>  
> +#ifdef CONFIG_SPARSEMEM
> +static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
> +{
> +	int i;
> +	for (i = 0; i < nr_pages; i++) {
> +		if (pfn_present(pfn + i))
> +			continue;
> +		else
> +			return -EINVAL;
> +	}
> +	return 0;
> +}
> +#else
> +static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_SPARSEMEM*/
> +
>  #ifdef CONFIG_NODES_SPAN_OTHER_NODES
>  bool early_pfn_in_nid(unsigned long pfn, int nid);
>  #else
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 49f7747..299747d 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -467,6 +467,19 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
>  	struct memory_notify arg;
>  
>  	lock_memory_hotplug();
> +	/*
> +	 * If system supports memory hot-remove, the memory may have been
> +	 * removed. So we check whether the memory has been removed or not.
> +	 *
> +	 * Note: When CONFIG_SPARSEMEM is defined, pfns_present() become
> +	 *       effective. If CONFIG_SPARSEMEM is not defined, pfns_present()
> +	 *       always returns 0.
> +	 */
> +	ret = pfns_present(pfn, nr_pages);
> +	if (ret) {
> +		unlock_memory_hotplug();
> +		return ret;
> +	}
>  	arg.start_pfn = pfn;
>  	arg.nr_pages = nr_pages;
>  	arg.status_change_nid = -1;