: http://old.lwn.net/2002/0124/kernel.php3
: "What Rik van Riel is up to."
:
:FWIW: In the original Article:
:
: http://lwn.net/Articles/3327/
:
:they say they've gon to a 3 level page table scheme for the Hammer
:port.
:
:-- Terry
They are still using a 2 level page table scheme in the linux
kernel. That is, they didn't try to integrate the 3-level hardware
in the hammer with the 2 level kernel representation. What they did
was create a fixed third level (or a fixed first level depending on how
you look at it). As far as Linux is concerned it is still a two-level
page table. This did simplify other areas of the kernel, e.g. no need
for 'himem' because all of physical memory is linearly mapped into
KVM, but the actual mechanism is not all that complex.
I think that in general the linux folks have found the copy-on-write
page table sharing to be less effective then they hoped. The only
advantage seems to occur with fork(). The programs that really need
it, like databases, do not share data via fork() but instead use
mmap() or SysV shared memory. Both Linux and FreeBSD wind up being
in the same boat. Being able to proactively share page table pages
will solve the problem for both systems.
-Matt
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