Subject: Re: [PATCH] 8xx: map_page() skip pinned region and tlbie debugging aid

From: Pantelis Antoniou <[email-masked]>
Date: Fri, 01 Jul 2005 10:01:59 +0300

Benjamin Herrenschmidt wrote:
> On Thu, 2005-06-30 at 14:05 -0400, Dan Malek wrote:
> 
>>On Jun 29, 2005, at 7:31 PM, Benjamin Herrenschmidt wrote:
>>
>>
>>> - The debate between Dan and me here is about the semantics of
>>>io_block_mapping().
>>
>>My point of discussion is this function needs to be much smarter than
>>simply allocating a virtual address space.  We need to track the calls
>>so that we can "grow" previous spaces.  A single io_block_mapping()
>>should not always allocate a new BAT, CAM or otherwise wired entry.
>>It has to know the alignment, size and amount of resource available.
>>For example, if an io_block_mapping() requests a 4M space, and it
>>isn't possible to wire such a size, we still need to keep track of that
>>such that a subsequent 4M request is combined into a space that
>>can be wired with an 8M entry.  We need to make it smart enough
>>to coalesce the spaces to maximize the use of the available and
>>minimal mapping resources.  If io_block_mapping() is just a simple
>>functions that decrements a pointer and sets a value in a register,
>>then you have already required the caller to know everything about
>>the mapping details, so why bother performing "hidden" arithmetic
>>that is likely to be known by the caller?  If we are going to change 
>>this
> 
> 
> Everyting ... but the virtual address, which is quite a bit :) My
> problem is really with virtual addresses beeing hard coded, which makes
> things complicated every time we try to do something with the kenrel
> virtual space. But ....
> 
> 
>>let's make it tru
>>y useful, so it understands the capabilities of the
>>processor, optimizes the resources, and keeps generic mapping
>>information so ioremap() doesn't care if it is mapped by BATs, CAMs,
>>or large pages.
> 
> 
>  ... I do agree that making it even smarter so it can coalesce block
> mappings with the same attributes would be "interesting".
> 
> Ben.
> 
> 

Let me pop in here.

My remote heap allocator has these properties, i.e. it can
coalesce adjucent areas if they are of the same "key".

Back to the depths which I now reside...

Regards

Pantelis