linux-kernel - Re: [PATCH 2/2] mm: remove_memory: Fix end

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Message-Id: <20130308133106.ec4f9810b69b105b8f70d82a@linux-foundation.org>
Date:	Fri, 8 Mar 2013 13:31:06 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Toshi Kani <toshi.kani@...com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	isimatu.yasuaki@...fujitsu.com, wency@...fujitsu.com,
	tangchen@...fujitsu.com
Subject: Re: [PATCH 2/2] mm: remove_memory: Fix end_pfn setting

On Fri,  8 Mar 2013 08:41:41 -0700 Toshi Kani <toshi.kani@...com> wrote:

> remove_memory() calls walk_memory_range() with [start_pfn, end_pfn),
> where end_pfn is exclusive in this range.  Therefore, end_pfn needs
> to be set to the next page of the end address.
> 
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1801,7 +1801,7 @@ int __ref remove_memory(int nid, u64 start, u64 size)
>  	int retry = 1;
>  
>  	start_pfn = PFN_DOWN(start);
> -	end_pfn = start_pfn + PFN_DOWN(size);
> +	end_pfn = PFN_UP(start + size - 1);
>  
>  	/*
>  	 * When CONFIG_MEMCG is on, one memory block may be used by other

That looks right, although these rounding/boundary things are always
hard.  I wonder if `start' and `size' are ever not multiples of
PAGE_SIZE..

How did you discover this?  Code inspection, or some runtime
malfunction?  Please always include this info when fixing bugs.

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