Re: [PATCHv8 07/12] mm: cma: Contiguous Memory Allocator added

[Ankita Garg]

Hi Michal,

On Wed, Dec 15, 2010 at 09:34:27PM +0100, Michal Nazarewicz wrote:
> The Contiguous Memory Allocator is a set of functions that lets
> one initialise a region of memory which then can be used to perform
> allocations of contiguous memory chunks from.
> 
> CMA allows for creation of private and non-private contexts.
> The former is reserved for CMA and no other kernel subsystem can
> use it.  The latter allows for movable pages to be allocated within
> CMA's managed memory so that it can be used for page cache when
> CMA devices do not use it.
> 
> Signed-off-by: Michal Nazarewicz <m.nazarewicz@xxxxxxxxxxx>
> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> ---
> 

<snip>

> +/************************* Initialise CMA *************************/
> +
> +unsigned long cma_reserve(unsigned long start, unsigned long size,
> +			  unsigned long alignment)
> +{
> +	pr_debug("%s(%p+%p/%p)\n", __func__, (void *)start, (void *)size,
> +		 (void *)alignment);
> +
> +	/* Sanity checks */
> +	if (!size || (alignment & (alignment - 1)))
> +		return (unsigned long)-EINVAL;
> +
> +	/* Sanitise input arguments */
> +	start = PAGE_ALIGN(start);
> +	size  = PAGE_ALIGN(size);
> +	if (alignment < PAGE_SIZE)
> +		alignment = PAGE_SIZE;
> +
> +	/* Reserve memory */
> +	if (start) {
> +		if (memblock_is_region_reserved(start, size) ||
> +		    memblock_reserve(start, size) < 0)
> +			return (unsigned long)-EBUSY;
> +	} else {
> +		/*
> +		 * Use __memblock_alloc_base() since
> +		 * memblock_alloc_base() panic()s.
> +		 */
> +		u64 addr = __memblock_alloc_base(size, alignment, 0);
> +		if (!addr) {
> +			return (unsigned long)-ENOMEM;
> +		} else if (addr + size > ~(unsigned long)0) {
> +			memblock_free(addr, size);
> +			return (unsigned long)-EOVERFLOW;
> +		} else {
> +			start = addr;
> +		}
> +	}
> +

Reserving the areas of memory belonging to CMA using memblock_reserve,
would preclude that range from the zones, due to which it would not be
available for buddy allocations right ?

> +	return start;
> +}
> +
> +

-- 
Regards,
Ankita Garg (ankita@xxxxxxxxxx)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India
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