Re: [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 <redacted>
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