linux-kernel - Re: [ RESEND PATCH v3] Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel

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Date:	Tue, 12 Jan 2010 17:04:33 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Zheng, Shaohui" <shaohui.zheng@...el.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"y-goto@...fujitsu.com" <y-goto@...fujitsu.com>,
	Dave Hansen <haveblue@...ibm.com>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [ RESEND PATCH v3] Memory-Hotplug: Fix the bug on interface
 /dev/mem for 64-bit kernel

On Tue, 12 Jan 2010 15:45:54 +0800
"Zheng, Shaohui" <shaohui.zheng@...el.com> wrote:

> Resend the v3 patch after reviewed by KAMEZAWA Hiroyuki. We still keep the 
> Old e820map, update variable max_pfn, max_low_pfn and high_memory only. 
> It is dependent on Fenguang's page_is_ram patch.
> 
> Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel
> 
> The new added memory can not be access by interface /dev/mem, because we do not
>  update the variable high_memory, max_pfn and max_low_pfn.
> 
> Memory hotplug still has critical issues for 32-bit kernel, and it is more 
> important for 64-bit kernel, we fix it on 64-bit first. We add a function 
> update_end_of_memory_vars in file arch/x86/mm/init.c to update these variables.
> 
> CC: Andi Kleen <ak@...ux.intel.com>
> CC: Li Haicheng <haicheng.li@...el.com>
> Reviewed-by: Wu Fengguang <fengguang.wu@...el.com>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Signed-off-by: Shaohui Zheng <shaohui.zheng@...el.com>

3 points...
1. I think this patch cannot be compiled in archs other than x86. Right ?
   IOW, please add static inline dummy...

2. pgdat->[start,end], totalram_pages etc...are updated at memory hotplug.
   Please place the hook nearby them.

3. I recommend you yo use memory hotplug notifier.
   If it's allowed, it will be cleaner.
   It seems there are no strict ordering to update parameters this patch touches.

Thanks,
-Kame





> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index d406c52..b6a85cc 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -1,6 +1,7 @@
>  #include <linux/initrd.h>
>  #include <linux/ioport.h>
>  #include <linux/swap.h>
> +#include <linux/bootmem.h>
>  
>  #include <asm/cacheflush.h>
>  #include <asm/e820.h>
> @@ -386,3 +387,24 @@ void free_initrd_mem(unsigned long start, unsigned long end)
>  	free_init_pages("initrd memory", start, end);
>  }
>  #endif
> +
> +/**
> + * After memory hotplug, the variable max_pfn, max_low_pfn and high_memory will
> + * be affected, it will be updated in this function. Memory hotplug still has
> + * critical issues on 32-bit kennel, it was more important on 64-bit kernel,
> + * so we update the variables for 64-bit kernel first, fix me in future for
> + * 32-bit kenrel.
> + */
> +void __meminit __attribute__((weak)) update_end_of_memory_vars(u64 start,
> +		u64 size)
> +{
> +#ifdef CONFIG_X86_64
> +	unsigned long start_pfn = start >> PAGE_SHIFT;
> +	unsigned long end_pfn = PFN_UP(start + size);
> +
> +	if (end_pfn > max_pfn) {
> +		max_low_pfn = max_pfn = end_pfn;
> +		high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
> +	}
> +#endif /* CONFIG_X86_64 */
> +}
> diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
> index b10ec49..84533a5 100644
> --- a/include/linux/bootmem.h
> +++ b/include/linux/bootmem.h
> @@ -13,6 +13,7 @@
>  
>  extern unsigned long max_low_pfn;
>  extern unsigned long min_low_pfn;
> +extern void update_end_of_memory_vars(u64 start, u64 size);
>  
>  /*
>   * highest page
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 030ce8a..3e94b23 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -523,6 +523,9 @@ int __ref add_memory(int nid, u64 start, u64 size)
>  		BUG_ON(ret);
>  	}
>  
> +	/* update max_pfn, max_low_pfn and high_memory */
> +	update_end_of_memory_vars(start, size);
> +
>  	goto out;
>  
>  error:
> 
> Thanks & Regards,
> Shaohui
> 
> 
> 

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