RE: ia64 ORDERROUNDDOWN issue

From: Luck, Tony <tony.luck_at_intel.com>
Date: 2006-11-30 05:34:24
> After some investigations I stated that count_node_pages() was computing 
> mem_data[1].min_pfn = 0, and mem_data[1].max_pfn = 20000 for node 1, 
> thus conflicting with the 0-2GB DMA memory range on node 0.
> This is due to the line:
>    start = ORDERROUNDDOWN(start);

There is an assumption here that the memory space on a node doesn't
cross a MAX_ORDER boundary ... and I'm not really sure where to go
with that.  Your patch papers over the problem for your specific case,
but as you point out it will just re-appear for someone who picks
a bigger MAX_ORDER.

Having nodes that are smaller than MAX_ORDER will cause confusion in
the allocator (if all the memory belonging to two nodes is in a
single MAX_ORDER page, the buddy allocator will give all the memory
to one node, and none to the other (won't it?).

> This should at least be checked in the count_node_pages() function.

Yes, a check should be made ... but count_node_pages() doesn't have
all the information if needs to do this (it just gets the start/size
for the memory on the node ... and it needs to check whether the
rounddown of the start address (or the roundup of the end address)
would cause conflicts with memory belonging to other nodes.

Do we need a "max_order" variable that could be adjusted to some lower
value that MAX_ORDER if we find the memory topology doesn't fit inside
the lines?  

-Tony
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Received on Thu Nov 30 06:13:11 2006

This archive was generated by hypermail 2.1.8 : 2006-11-30 06:13:34 EST