Dave Hansen wrote:

On Tue, 2004-08-31 at 15:55, Hiroyuki KAMEZAWA wrote:

quoted

Dave Hansen wrote:

quoted

On Tue, 2004-08-31 at 03:41, Hiroyuki KAMEZAWA wrote:

quoted

+static void __init calculate_aligned_end(struct zone *zone,
+					 unsigned long start_pfn,
+					 int nr_pages)

...

quoted

+		end_address = (zone->zone_start_pfn + end_idx) << PAGE_SHIFT;
+#ifndef CONFIG_DISCONTIGMEM
+		reserve_bootmem(end_address,PAGE_SIZE);
+#else
+		reserve_bootmem_node(zone->zone_pgdat,end_address,PAGE_SIZE);
+#endif
+	}
+	return;
+}

What if someone has already reserved that address?  You might not be
able to grow the zone, right?

1) If someone has already reserved that address,  it (the page) will not join to
  buddy allocator and it's no problem.

2) No, I can grow the zone.
  A reserved page is the last page of "not aligned contiguous mem_map", not zone.

I answer your question ?

If the end of the zone isn't aligned, you simply waste memory until it becomes aligned, right?

No. I waste just one page, the end page of mem_map.
When the end of mem_map is not aligned, there are 2 cases.

case 1) length of mem_map is even number.
 -------------------------------
 |  |  |  |  |C |  |B |  |A | X|  no-page-area    order=0
 -------------------------------
 |     |     |C    |B    |                        order=1
 -------------------------
 |           |C          |                        order=2
 -------------------------
X is reserved and will not join to buddy system.
By doing this,
page "A" has no boddy in order=0, "X" is reserved.
page "B" has no buddy in order=1, "A" is order 0.
page "C" has no buddy in order=2, "A" is order 0.
..........

case 2) length of mem_map is odd number.
-----------------------------
 |  |  |  |  |C |  |B |  |X |    no-page-area    order=0
 ----------------------------
 |     |     |C    |B    |                       order=1
 -------------------------
 |           |C          |                       order=2
 -------------------------
page "B" has no buddy in order=1, X is reserved.
.........

Access to no-page-area in buddy system does not occur.

-- Kame

-- 
--the clue is these footmarks leading to the door.--
KAMEZAWA Hiroyuki [off-list ref]

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