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
