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SubjectRe: [PATCHv8 07/12] mm: cma: Contiguous Memory Allocator added
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@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> ---
>

<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@in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India


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