mmu: Anonymous memory demand paging

Switch to demand paging for anonymous virtual memory.

I used SPECjvm2008 to verify performance impact. The numbers are mostly
the same with few exceptions, most visible in the 'serial' benchmark.
However, there's quite a lot of variance between SPECjvm2008 runs so I
wouldn't read too much into them.

As we need the demand paging mechanism and the performance numbers
suggest that the implementation is reasonable, I'd merge the patch as-is
and see optimize it later.

  Before:

    Running specJVM2008 benchmarks on an OSV guest.
    Score on compiler.compiler: 331.23 ops/m
    Score on compiler.sunflow: 131.87 ops/m
    Score on compress: 118.33 ops/m
    Score on crypto.aes: 41.34 ops/m
    Score on crypto.rsa: 204.12 ops/m
    Score on crypto.signverify: 196.49 ops/m
    Score on derby: 170.12 ops/m
    Score on mpegaudio: 70.37 ops/m
    Score on scimark.fft.large: 36.68 ops/m
    Score on scimark.lu.large: 13.43 ops/m
    Score on scimark.sor.large: 22.29 ops/m
    Score on scimark.sparse.large: 29.35 ops/m
    Score on scimark.fft.small: 195.19 ops/m
    Score on scimark.lu.small: 233.95 ops/m
    Score on scimark.sor.small: 90.86 ops/m
    Score on scimark.sparse.small: 64.11 ops/m
    Score on scimark.monte_carlo: 145.44 ops/m
    Score on serial: 94.95 ops/m
    Score on sunflow: 73.24 ops/m
    Score on xml.transform: 207.82 ops/m
    Score on xml.validation: 343.59 ops/m

  After:

    Score on compiler.compiler: 346.78 ops/m
    Score on compiler.sunflow: 132.58 ops/m
    Score on compress: 116.05 ops/m
    Score on crypto.aes: 40.26 ops/m
    Score on crypto.rsa: 206.67 ops/m
    Score on crypto.signverify: 194.47 ops/m
    Score on derby: 175.22 ops/m
    Score on mpegaudio: 76.18 ops/m
    Score on scimark.fft.large: 34.34 ops/m
    Score on scimark.lu.large: 15.00 ops/m
    Score on scimark.sor.large: 24.80 ops/m
    Score on scimark.sparse.large: 33.10 ops/m
    Score on scimark.fft.small: 168.67 ops/m
    Score on scimark.lu.small: 236.14 ops/m
    Score on scimark.sor.small: 110.77 ops/m
    Score on scimark.sparse.small: 121.29 ops/m
    Score on scimark.monte_carlo: 146.03 ops/m
    Score on serial: 87.03 ops/m
    Score on sunflow: 77.33 ops/m
    Score on xml.transform: 205.73 ops/m
    Score on xml.validation: 351.97 ops/m

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
mmu: MAP_POPULATE support for anon mmap()

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
tests: Anonymous demand paging microbenchmark

This adds a simple mmap microbenchmark that can be run on both OSv and
Linux.  The benchmark mmaps memory for various sizes and touches the
mmap'd memory in 4K increments to fault in memory.  The benchmark also
repeats the same tests using MAP_POPULATE for reference.

OSv page faults are slightly slower than Linux on first iteration but
faster on subsequent iterations after host operating system has faulted
in memory for the guest.

I've included full numbers on 2-core Sandy Bridge i7 for a OSv guest,
Linux guest, and Linux host below:

  OSv guest
  ---------

  Iteration 1

       time (seconds)
   MiB demand populate
     1 0.004  0.000
     2 0.000  0.000
     4 0.000  0.000
     8 0.001  0.000
    16 0.003  0.000
    32 0.007  0.000
    64 0.013  0.000
   128 0.024  0.000
   256 0.052  0.001
   512 0.229  0.002
  1024 0.587  0.005

  Iteration 2

       time (seconds)
   MiB demand populate
     1 0.001  0.000
     2 0.000  0.000
     4 0.000  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.004  0.000
    64 0.010  0.000
   128 0.019  0.001
   256 0.036  0.001
   512 0.069  0.002
  1024 0.137  0.005

  Iteration 3

       time (seconds)
   MiB demand populate
     1 0.001  0.000
     2 0.000  0.000
     4 0.000  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.005  0.000
    64 0.010  0.000
   128 0.020  0.000
   256 0.039  0.001
   512 0.087  0.002
  1024 0.138  0.005

  Iteration 4

       time (seconds)
   MiB demand populate
     1 0.001  0.000
     2 0.000  0.000
     4 0.000  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.004  0.000
    64 0.012  0.000
   128 0.025  0.001
   256 0.040  0.001
   512 0.082  0.002
  1024 0.138  0.005

  Iteration 5

       time (seconds)
   MiB demand populate
     1 0.001  0.000
     2 0.000  0.000
     4 0.000  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.004  0.000
    64 0.012  0.000
   128 0.028  0.001
   256 0.040  0.001
   512 0.082  0.002
  1024 0.166  0.005

  Linux guest
  -----------

  Iteration 1

       time (seconds)
   MiB demand populate
     1 0.001  0.000
     2 0.001  0.000
     4 0.002  0.000
     8 0.003  0.000
    16 0.005  0.000
    32 0.008  0.000
    64 0.015  0.000
   128 0.151  0.001
   256 0.090  0.001
   512 0.266  0.003
  1024 0.401  0.006

  Iteration 2

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.000  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.005  0.000
    64 0.009  0.000
   128 0.019  0.001
   256 0.037  0.001
   512 0.072  0.003
  1024 0.144  0.006

  Iteration 3

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.001  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.005  0.000
    64 0.010  0.000
   128 0.019  0.001
   256 0.037  0.001
   512 0.072  0.003
  1024 0.143  0.006

  Iteration 4

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.001  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.003  0.000
    32 0.005  0.000
    64 0.010  0.000
   128 0.020  0.001
   256 0.038  0.001
   512 0.073  0.003
  1024 0.143  0.006

  Iteration 5

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.001  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.003  0.000
    32 0.005  0.000
    64 0.010  0.000
   128 0.020  0.001
   256 0.037  0.001
   512 0.072  0.003
  1024 0.144  0.006

  Linux host
  ----------

  Iteration 1

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.001  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.005  0.000
    64 0.009  0.000
   128 0.019  0.001
   256 0.035  0.001
   512 0.152  0.003
  1024 0.286  0.011

  Iteration 2

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.000  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.004  0.000
    64 0.010  0.000
   128 0.018  0.001
   256 0.035  0.001
   512 0.192  0.003
  1024 0.334  0.011

  Iteration 3

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.000  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.004  0.000
    64 0.010  0.000
   128 0.018  0.001
   256 0.035  0.001
   512 0.194  0.003
  1024 0.329  0.011

  Iteration 4

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.000  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.004  0.000
    64 0.010  0.000
   128 0.018  0.001
   256 0.036  0.001
   512 0.138  0.003
  1024 0.341  0.011

  Iteration 5

       time (seconds)
   MiB demand populate
     1 0.000  0.000
     2 0.000  0.000
     4 0.001  0.000
     8 0.001  0.000
    16 0.002  0.000
    32 0.004  0.000
    64 0.010  0.000
   128 0.018  0.001
   256 0.035  0.001
   512 0.135  0.002
  1024 0.324  0.011

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
tests: mincore() tests for demand paging

As suggested by Nadav, add tests for mincore() interraction with demand
paging.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>