CA-423816 avoid double counting VM overhead memory (#7005)

When we are using a known memory configuration it includes the overhead.
So we only have to add it when we create a new configuration.

Localhost migration in a loop before and after the patch, memory
reported by list_domains -memory -bytes:

  Before:
```
  id |         uuid |  state |  tot bytes |  max bytes | shadow bytes
  17 | 8fc1ada1-... |    B H | 4296003584 | 4336898048 |     36700160
  18 | 8fc1ada1-... |    B H | 4296003584 | 4376743936 |     36700160
  19 | 8fc1ada1-... |    B H | 4296003584 | 4416589824 |     36700160
  20 | 8fc1ada1-... |    B H | 4296003584 | 4456435712 |     36700160
  21 | 8fc1ada1-... |    B H | 4296003584 | 4496281600 |     36700160
  22 | 8fc1ada1-... |    B H | 4296003584 | 4536127488 |     36700160
  23 | 8fc1ada1-... |    B H | 4296003584 | 4575973376 |     36700160
  24 | 8fc1ada1-... |    B H | 4296003584 | 4615819264 |     36700160
  25 | 8fc1ada1-... |    B H | 4296003584 | 4655665152 |     36700160
  26 | 8fc1ada1-... |    B H | 4296003584 | 4695511040 |     36700160
```
  After:
```
  id |         uuid |  state |  tot bytes |  max bytes | shadow bytes
  27 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  28 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  29 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  30 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  31 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  32 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  33 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  34 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  35 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
  36 | 8fc1ada1-... |    B H | 4256157696 | 4297052160 |     36700160
```
Based on work by Edwin Torok.

Author: robhoes

ocaml/quicktest/quicktest_vm_memory.ml

@@ -12,7 +12,7 @@ let check_tasks tasks =
 let one t ~host ~vm ~workload_vm n =
   Trace.with_ __FUNCTION__ @@ fun scope ->
   workload t ~host ~workload_vm ;
-  let vms = fill_mem_n t ~workaround_migration:true ~host ~vm ~n in
+  let vms = fill_mem_n t ~workaround_migration:false ~host ~vm ~n in
 
   let migration_host, migration_vm = List.nth vms 0 in
 

ocaml/xenopsd/xc/xenops_server_xen.ml

@@ -1852,13 +1852,16 @@ module VM = struct
                         "VM = %s; using memory_dynamic_min = %Ld and \
                          memory_dynamic_max = %Ld"
                         vm.Vm.id vm.memory_dynamic_min vm.memory_dynamic_max ;
-                      (vm.memory_dynamic_min, vm.memory_dynamic_max, None)
+                      ( vm.memory_dynamic_min +++ overhead_bytes
+                      , vm.memory_dynamic_max +++ overhead_bytes
+                      , None
+                      )
                     )
               in
-              let min_kib = kib_of_bytes_used (min_bytes +++ overhead_bytes)
+              let min_kib = kib_of_bytes_used min_bytes
               and memory_total_source_kib =
                 Option.map kib_of_bytes_used memory_total_source_bytes
-              and max_kib = kib_of_bytes_used (max_bytes +++ overhead_bytes) in
+              and max_kib = kib_of_bytes_used max_bytes in
               (* XXX: we would like to be able to cancel an in-progress
                  with_reservation *)
               let dbg = Xenops_task.get_dbg task in