--On Wednesday, February 04, 2004 14:07:52 -0500 "Richard B. Johnson"
[off-list ref] wrote:

If this is an Intel x86 machine, it is impossible for pages
to get fragmented in the first place. The hardware allows any
page, from anywhere in memory, to be concatenated into linear
virtual address space. Even the kernel address space is virtual.
The only time you need physically-adjacent pages is if you
are doing DMA that is more than a page-length at a time. The
kernel keeps a bunch of those pages around for just that
purpose.

So, if you are making a "memory defragmenter", it is a CPU time-sink.

Um, wrong answer.  When you ask for more than one page from the buddy
allocator  (order greater than 0) it always returns physically contiguous
pages.

Also, one of the near-term goals in VM is to be able to allocate and free
large pages from the main memory pools, which requires that something like
order 9 or 10 allocations (based on the architecture) succeed.

Dave McCracken

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