[PATCH] drivers/base: export gpl (un)register_memory_notifier

[Jan-Bernd Themann]

Dave Hansen <haveblue at us.ibm.com> wrote on 15.02.2008 17:55:38:

> I've been thinking about that, and I don't think you really *need* to
> keep a comprehensive map like that. 
> 
> When the memory is in a particular configuration (range of memory
> present along with unique set of holes) you get a unique ehea_bmap
> configuration.  That layout is completely predictable.
> 
> So, if at any time you want to figure out what the ehea_bmap address for
> a particular *Linux* virtual address is, you just need to pretend that
> you're creating the entire ehea_bmap, use the same algorithm and figure
> out host you would have placed things, and use that result.
> 
> Now, that's going to be a slow, crappy linear search (but maybe not as
> slow as recreating the silly thing).  So, you might eventually run into
> some scalability problems with a lot of packets going around.  But, I'd
> be curious if you do in practice.

Up to 14 addresses translation per packet (sg_list) might be required on 
the
transmit side. On receive side it is only 1. Most packets require only 
very few
translations (1 or sometimes more)  translations. However, with more then 
700.000 
packets per second this approach does not seem reasonable from performance
perspective when memory is fragmented as you described.

> 
> The other idea is that you create a mapping that is precisely 1:1 with
> kernel memory.  Let's say you have two sections present, 0 and 100.  You
> have a high_section_index of 100, and you vmalloc() a 100 entry array.
> 
> You need to create a *CONTIGUOUS* ehea map?  Create one like this:
> 
> EHEA_VADDR->Linux Section
> 0->0
> 1->0
> 2->0
> 3->0
> ...
> 100->100
> 
> It's contiguous.  Each area points to a valid Linux memory address.
> It's also discernable in O(1) to what EHEA address a given Linux address
> is mapped.  You just have a couple of duplicate entries. 

This has a serious issues with constraint I mentions in the previous mail: 

"- MRs can have a maximum size of the memory available under linux"

The requirement is not met that the memory region must not be 
larger then the available memory for that partition. The "create MR" 
H_CALL
will fails (we tried this and discussed with FW development)


Regards,
Jan-Bernd & Christoph
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