Fix machdep.pmap_mmu_optimize (currently off by default in commit 1ac5304a10366be7ed3129ceee7ca94beb0f3183 ). Affects apache and rtorrent for sure.
"might be fixed here: a44410dd8663abb121417692995d3b365f32fd6e
update: it's not fixed"
kernel - Correct second edge-case for machdep.pmap_mmu_optimize
* The pmap_release*() code was previously optimized to not invalidate
on pml4, pdp, pd, or pt pte's, only on terminal ptes. This invalidation
interferes with the PT replacement that the pmap_mmu_optimize feature
* The bug generally would only occur when memory is mmap()'d and munmap()'d
multiple times, which something like postgres will not do, but which
rtorrent and other programs will do.
* Correctly invalidate page tables (use invltlb) when PT pte's are replaced.
* Requires further testing. Default for this feature is still off.