linux-kernel - Re: [patch 02/41] cpu alloc: The allocator

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Date:	Wed, 04 Jun 2008 07:48:34 -0700
From:	Mike Travis <travis@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Christoph Lameter <clameter@....com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [patch 02/41] cpu alloc: The allocator


Andrew Morton wrote:
...
>> +/*
>> + * Mark an object as used in the cpu_alloc_map
>> + *
>> + * Must hold cpu_alloc_map_lock
>> + */
>> +static void set_map(int start, int length)
>> +{
>> +	while (length-- > 0)
>> +		__set_bit(start++, cpu_alloc_map);
>> +}
> 
> bitmap_fill()?
> 
>> +/*
>> + * Mark an area as freed.
>> + *
>> + * Must hold cpu_alloc_map_lock
>> + */
>> +static void clear_map(int start, int length)
>> +{
>> +	while (length-- > 0)
>> +		__clear_bit(start++, cpu_alloc_map);
>> +}
> 
> bitmap_zero()?
...
>> +void *cpu_alloc(unsigned long size, gfp_t gfpflags, unsigned long align)
>> +{
>> +	unsigned long start;
>> +	int units = size_to_units(size);
>> +	void *ptr;
>> +	int first;
>> +	unsigned long flags;
>> +
>> +	if (!size)
>> +		return ZERO_SIZE_PTR;
> 
> OK, so we reuse ZERO_SIZE_PTR from kmalloc.
> 
>> +	spin_lock_irqsave(&cpu_alloc_map_lock, flags);
>> +
>> +	first = 1;
>> +	start = first_free;
>> +
>> +	for ( ; ; ) {
>> +
>> +		start = find_next_zero_bit(cpu_alloc_map, UNITS, start);
>> +		if (start >= UNITS)
>> +			goto out_of_memory;
>> +
>> +		if (first)
>> +			first_free = start;
>> +
>> +		/*
>> +		 * Check alignment and that there is enough space after
>> +		 * the starting unit.
>> +		 */
>> +		if (start % (align / UNIT_SIZE) == 0 &&
>> +			find_next_bit(cpu_alloc_map, UNITS, start + 1)
>> +							>= start + units)
>> +				break;
>> +		start++;
>> +		first = 0;
>> +	}
> 
> This is kinda bitmap_find_free_region(), only bitmap_find_free_region()
> isn't quite strong enough.
> 
> Generally I think it would have been better if you had added new
> primitives to the bitmap library (or enhanced existing ones) and used
> them here, rather than implementing private functionality.

Hi Andrew,

I've sort of inherited this now...

So are you suggesting that we add new bitmap primitives to:

	bitmap_fill_offset(bitmap, start, nbits)   /* start at bitmap[start] */
	bitmap_zero_offset(bitmap, start, nbits)
	bitmap_find_free_area(bitmap, nbits, size, align)  /* size not order */

Thanks,
Mike 
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