Revert "OS-8005 bhyve memory pressure needs to target ARC better (#354)"
This reverts commit a6033573eedd94118d2b9e65f45deca0bf4b42f7.

*** 18,28 ****
   *
   * CDDL HEADER END
   */
  /*
   * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
!  * Copyright 2020 Joyent, Inc.
   * Copyright (c) 2011, 2018 by Delphix. All rights reserved.
   * Copyright (c) 2014 by Saso Kiselkov. All rights reserved.
   * Copyright 2017 Nexenta Systems, Inc.  All rights reserved.
   * Copyright (c) 2011, 2019, Delphix. All rights reserved.
   * Copyright (c) 2020, George Amanakis. All rights reserved.
--- 18,28 ----
   *
   * CDDL HEADER END
   */
  /*
   * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
!  * Copyright (c) 2019, Joyent, Inc.
   * Copyright (c) 2011, 2018 by Delphix. All rights reserved.
   * Copyright (c) 2014 by Saso Kiselkov. All rights reserved.
   * Copyright 2017 Nexenta Systems, Inc.  All rights reserved.
   * Copyright (c) 2011, 2019, Delphix. All rights reserved.
   * Copyright (c) 2020, George Amanakis. All rights reserved.
*** 4542,4552 ****
          FMR_LOTSFREE,
          FMR_SWAPFS_MINFREE,
          FMR_PAGES_PP_MAXIMUM,
          FMR_HEAP_ARENA,
          FMR_ZIO_ARENA,
-         FMR_VIRT_MACHINE,       /* 'VM' seems ambiguous in this context */
  } free_memory_reason_t;
  
  int64_t last_free_memory;
  free_memory_reason_t last_free_reason;
  
--- 4542,4551 ----
*** 4558,4610 ****
  /*
   * Additional reserve of pages for swapfs.
   */
  int64_t arc_swapfs_reserve = 64;
  
- static volatile uint64_t arc_virt_machine_reserved;
- 
  /*
-  * XXX: A possible concern is that we allow arc_virt_machine_reserved to
-  * get so large that we cause the arc to perform a lot of additional
-  * work to keep the arc extremely small. We may want to set limits to
-  * the size of arc_virt_machine_reserved and disallow reservations
-  * beyond that limit.
-  */
- int
- arc_virt_machine_reserve(size_t pages)
- {
-         uint64_t newv;
- 
-         newv = atomic_add_64_nv(&arc_virt_machine_reserved, pages);
- 
-         /*
-          * Since arc_virt_machine_reserved effectively lowers arc_c_max
-          * as needed for vmm memory, if this request would put the arc
-          * under arc_c_min, we reject it.  arc_c_min should be a value that
-          * ensures reasonable performance for non-VMM stuff, as well as keep
-          * us from dipping below lotsfree, which could trigger the pager
-          * (and send the system toa grinding halt while it pages).
-          *
-          * XXX: This is a bit hacky and might be better done w/ a mutex
-          * instead of atomic ops.
-          */
-         if (newv + arc_c_min > arc_c_max) {
-                 atomic_add_64(&arc_virt_machine_reserved, -(int64_t)pages);
-                 return (ENOMEM);
-         }
- 
-         zthr_wakeup(arc_reap_zthr);
-         return (0);
- }
- 
- void
- arc_virt_machine_release(size_t pages)
- {
-         atomic_add_64(&arc_virt_machine_reserved, -(int64_t)pages);
- }
- 
- /*
   * Return the amount of memory that can be consumed before reclaim will be
   * needed.  Positive if there is sufficient free memory, negative indicates
   * the amount of memory that needs to be freed up.
   */
  static int64_t
--- 4557,4567 ----
*** 4663,4683 ****
          if (n < lowest) {
                  lowest = n;
                  r = FMR_PAGES_PP_MAXIMUM;
          }
  
-         /*
-          * Check that we have enough memory for any virtual machines that
-          * are running or starting. We add desfree to keep us out of
-          * particularly dire circumstances.
-          */
-         n = PAGESIZE * (availrmem - arc_virt_machine_reserved - desfree);
-         if (n < lowest) {
-                 lowest = n;
-                 r = FMR_VIRT_MACHINE;
-         }
- 
  #if defined(__i386)
          /*
           * If we're on an i386 platform, it's possible that we'll exhaust the
           * kernel heap space before we ever run out of available physical
           * memory.  Most checks of the size of the heap_area compare against
--- 4620,4629 ----