Re: [Lhms-devel] Re: [RFC] free_area[] bitmap elimination [0/3]

[Hiroyuki KAMEZAWA <kamezawa.hiroyu@jp.fujitsu.com>]

Hi,

William Lee Irwin III wrote:

> William Lee Irwin III wrote:
> 
>>>In __free_pages_bulk() changing BUG_ON(bad_range(zone, buddy1)) to
>>>if (bad_range(zone, buddy1)) break; should fix this. The start of
>>>the zone must be aligned to MAX_ORDER so buddy2 doesn't need checks.
>>>It may be worthwhile to make a distinction the bounds checks and the
>>>zone check and to BUG_ON() the zone check in isolation and not repeat
>>>the bounds check for the validity check.
> 
> 
> On Sat, Aug 21, 2004 at 02:37:56PM +0900, Hiroyuki KAMEZAWA wrote:
> 
>>Okay, I understand several BUG_ON() are needless.
>>I'll be more carefull to recognize what is checked.
> 
> 
> It's not that it's needless, it's that beforehand the bitmap rounding
> up to an even number ensured the __test_and_change_bit() check would
> prevent the bounds check from ever failing, but after the bitmap is
> eliminated, the bounds check is needed to see if we're even examining
> a valid page structure for whether the page can be merged.
> 
> 
Oh, I said these 2 lines are needless ;) ,sorry for my vagueness.
     buddy2 = base + page_idx;
(*) BUG_ON(bad_range(zone, buddy1));
(*) BUG_ON(bad_range(zone, buddy2));

I understand a test before accessing "buddy1" is necessary.

But as I mentioned in other mail, I'm afraid of memory hole in zone.
This cannot be detected by simple range check.
Is this special case of IA64 ? (I don't know other archs than i386 and IA64)

I think
+ if (!pfn_valid(buddy1))
+     break;
will work enough if pfn_valid() works correctly fot zone with hole.

If ZONE is not MAX_ORDER aligned,
if (bad_range(zone,buddy1))
     break;
will be needed too.


-- KAME

-- 
--the clue is these footmarks leading to the door.--
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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