Hi,
On Tue, 8 Feb 2000 13:01:44 +0100, Jamie Lokier
<lkd@tantalophile.demon.co.uk> said:
> Linus Torvalds wrote:
>> The zones have to be aligned, there's no question about that. The
>> preferred alignment is in the megabyte range, rather than in individual
>> pages. In fact, I would suggest always making sure that it is aligned to
>> the largest order that get_free_page() supports, and I think that's true
>> of all current architectures..
> I don't see why it's necessary though. The allocator should simply use
> absolute address values for pairing instead of zone-relative
> addresses.. is there anything more to it than that?
Yes --- you need 8k allocations to be 8k-aligned physically, and 64k
allocations to be 64k-aligned, etc. Just to think of one example, Intel
MTRR absolutely requires that the address of a memory range is a
multiple of the size of the range, and you need aligned zones to create
such regions.
This needn't be a problem --- you can easily create a zone aligned at a
large (eg. 16MB) granularity, without filling it with free pages. As an
example, the low-memory zone doesn't populate the free page list with
pages in the 640k-1M hole. Just because your physical page region isn't
aligned nicely doesn't mean you cannot align the zone itself.
--Stephen
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