[PATCH 0/6] [RFC] Sizing zones and holes in an architecture independent manner

[Mel Gorman]

On Wed, 12 Apr 2006, Luck, Tony wrote:

> On Wed, Apr 12, 2006 at 05:00:32PM +0100, Mel Gorman wrote:
>> Patch is attached as 105-ia64_use_init_nodes.patch until I beat sense into
>> my mail setup. I've added Bob Picco to the cc list as he will hit the same
>> issue with whitespace corruption.
>
> Next I tried building a "generic" kernel (using arch/ia64/defconfig). This
> has NUMA=y and DISCONTIG=y).  This crashes with the following console log.
>
>
> <snipped>
> add_active_range(0, 0, 4096): New
> add_active_range(0, 0, 131072): New
> add_active_range(0, 0, 131072): New
> add_active_range(0, 393216, 523264): New
> add_active_range(0, 393216, 523264): New
> add_active_range(0, 393216, 524288): New
> add_active_range(0, 393216, 524288): New

This is where it started going wrong. I did not expect add_active_range() 
to be called with overlapping PFNs so they were not getting merged. If 
they were getting merged correctly, I'd expect the output to be

add_active_range(0, 0, 4096): New
add_active_range(0, 0, 131072): Merging forward
add_active_range(0, 0, 131072): Merging forward
add_active_range(0, 393216, 523264): New
add_active_range(0, 393216, 523264): Merging forward
add_active_range(0, 393216, 524288): Merging forward
add_active_range(0, 393216, 524288): Merging forward

> Virtual mem_map starts at 0xa0007ffffe400000
> Dumping sorted node map
> entry 0: 0  0 -> 131072
> entry 1: 0  0 -> 4096
> entry 2: 0  0 -> 131072
> entry 3: 0  393216 -> 523264
> entry 4: 0  393216 -> 524288
> entry 5: 0  393216 -> 524288
> entry 6: 0  393216 -> 523264
> Hole found index 0: 0 -> 0
> prev_end > start_pfn : 131072 > 0

And here is where it goes BLAM. Without the debugging patch, the check is 
just;

BUG_ON(prev_end_pfn > start_pfn);

The error I was *expecting* to catch was an unsorted node map. It's just 
nice it caught this situation as well. It'll take a while to fix this up 
properly.

Thanks

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab