Date: Wed, 25 May 2005 13:40:56 -0700
From: Mike Kravetz <kravetz@us.ibm.com>
To: Mel Gorman <mel@csn.ul.ie>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@osdl.org
Subject: Re: Avoiding external fragmentation with a placement policy Version 11
Message-ID: <20050525204056.GA9257@w-mikek2.ibm.com>
References: <20050522200507.6ED7AECFC@skynet.csn.ul.ie>
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On Sun, May 22, 2005 at 09:05:07PM +0100, Mel Gorman wrote:
>  /*
> + * Calculate the size of the zone->usemap
> + */
> +static unsigned long __init usemap_size(unsigned long zonesize) {
> +	unsigned long usemapsize;
> +
> +	/* - Number of MAX_ORDER blocks in the zone */
> +	usemapsize = (zonesize + (1 << (MAX_ORDER-1))) >> (MAX_ORDER-1);
> +
> +	/* - BITS_PER_ALLOC_TYPE bits to record what type of block it is */
> +	usemapsize = (usemapsize * BITS_PER_ALLOC_TYPE + (sizeof(unsigned long)*8)) / 8;
> +
> +	return L1_CACHE_ALIGN(usemapsize);
> +}

In the first calculation, I think you are trying to 'round up'.  If this
is the case, then I believe the calculation should be:

usemapsize = (zonesize + ((1 << (MAX_ORDER-1)) - 1) >> (MAX_ORDER-1);

I don't know if there is a similar issue in the second calculation.
Arithmetic is not one of my strengths.

-- 
Mike
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