Christoph Lameter writes:

The most expensive operation in the page fault handler is (apart of SMP
locking overhead) the zeroing of the page. This zeroing means that all
cachelines of the faulted page (on Altix that means all 128 cachelines of
128 byte each) must be loaded and later written back. This patch allows to
avoid having to load all cachelines if only a part of the cachelines of
that page is needed immediately after the fault.

On ppc64 we avoid having to zero newly-allocated page table pages by
using a slab cache for them, with a constructor function that zeroes
them.  Page table pages naturally end up being full of zeroes when
they are freed, since ptep_get_and_clear, pmd_clear or pgd_clear has
been used on every non-zero entry by that stage.  Thus there is no
extra work required either when allocating them or freeing them.

I don't see any point in your patches for systems which don't have
some magic hardware for zeroing pages.  Your patch seems like a lot of
extra code that only benefits a very small number of machines.

Paul.
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