replace locking in swap reservation with fetchadd

[kmacy]

Summary

This is a straightforward conversion of the locking around swap_reservation and ui_vmsize to use atomic_fetchadd. This gives a 40% speedup on brk1_processes in will-it-scale. Moving the bottleneck to the invl_gen_mtx. The atomics again become bottlenecks if D15231 is put in place and so ultimately a more sophisticated pcpu scheme is warranted.

I realized I may have to keep the locked version around for ppc32 and MIPS. Suggestions welcome, otherwise I'll abandon.

[kib]

sys/vm/swap_pager.c

208

I would not call this variable 'new'.

Also, I do not believe that the patch compiles on 32bit architectures.

295

This does not compole for kernels without RACCT.