Subject: Re: [PATCH v4 3/13] memory-hotplug : check whether memory is present or not

From: Wen Congyang <[email-masked]>
Date: Wed, 18 Jul 2012 18:25:14 +0800

At 07/18/2012 06:07 PM, Yasuaki Ishimatsu Wrote:
> 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.
> 
> 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 |   21 +++++++++++++++++++++
>  mm/memory_hotplug.c    |   13 +++++++++++++
>  2 files changed, 34 insertions(+)
> 
> Index: linux-3.5-rc6/include/linux/mmzone.h
> ===================================================================
> --- linux-3.5-rc6.orig/include/linux/mmzone.h	2012-07-08 09:23:56.000000000 +0900
> +++ linux-3.5-rc6/include/linux/mmzone.h	2012-07-17 16:10:21.588186145 +0900
> @@ -1168,6 +1168,27 @@ 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 + 1))
> +			continue;
> +		else {
> +			unlock_memory_hotplug();

Why do you unlock memory hotplug here? The caller will do it.

Thanks
Wen Congyang

> +			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
> Index: linux-3.5-rc6/mm/memory_hotplug.c
> ===================================================================
> --- linux-3.5-rc6.orig/mm/memory_hotplug.c	2012-07-17 14:26:40.000000000 +0900
> +++ linux-3.5-rc6/mm/memory_hotplug.c	2012-07-17 16:09:50.070580170 +0900
> @@ -467,6 +467,19 @@ int __ref online_pages(unsigned long pfn
>  	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;
> 
>