Re: [Lhms-devel] Re: [RFC] buddy allocator without bitmap(2) [1/3]

Hiroyuki KAMEZAWA
2004-08-31T23:31:12Z

Dave Hansen wrote:

> On Tue, 2004-08-31 at 15:55, Hiroyuki KAMEZAWA wrote:
>
>>Dave Hansen wrote:
>>
>>
>>>On Tue, 2004-08-31 at 03:41, Hiroyuki KAMEZAWA wrote:
>>>
>>>
>>>>+static void __init calculate_aligned_end(struct zone *zone,
>>>>+ unsigned long start_pfn,
>>>>+ int nr_pages)
>>>
>>>...
>>>
>>>
>>>>+ 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 <kamezawa.hiroyu@jp.fujitsu.com>