CA-422187: create an emergency reserve of pages

Do not let domains fully use up all available memory on the host,
we have too many unexplained bugs in this area.

As a workaround try to reserve some amount (e.g. 256MiB) that domains cannot
normally use from XAPI's point of view.
Then during parallel domain construction this emergency reserve can be used by
Xen.

Signed-off-by: Edwin Török <[email protected]>

Author: edwintorok

doc/content/design/numa.md

@@ -112,7 +112,7 @@ This function receives as arguments a domain ID and the number of nodes
 this domain is using (acquired using `domain_get_numa_info_node_pages`)
 
 The number of NUMA nodes of the host (not domain) is reported by
-`Xenctrl.physinfo` which returns a value of type `physinfo`.
+`Xenctrlext.physinfo` which returns a value of type `physinfo`.
 
 ```diff
     index b4579862ff..491bd3fc73 100644

doc/content/xenopsd/walkthroughs/VM.build/Domain.build.md

@@ -64,7 +64,7 @@ to call:
     [wait_xen_free_mem](https://github.com/xapi-project/xen-api/blob/master/ocaml/xenopsd/xc/domain.ml#L236-L272)
     to wait (if necessary), for the Xen memory scrubber to catch up reclaiming memory.
     It
-    1. calls `Xenctrl.physinfo` which returns:
+    1. calls `Xenctrlext.physinfo` which returns:
        - `hostinfo.free_pages` - the free and already scrubbed pages (available)
        - `host.scrub_pages` - the not yet scrubbed pages (not yet available)
     2. repeats this until a timeout as long as `free_pages` is *lower*

ocaml/libs/xenctrl-ext/xenctrlext.ml

@@ -131,3 +131,8 @@ let domain_claim_pages handle domid ?(numa_node = NumaNode.none) nr_pages =
 let get_nr_nodes handle =
   let info = numainfo handle in
   Array.length info.memory
+
+let physinfo xc =
+  let info = Xenctrl.physinfo xc in
+  let emergency_reserve_pages = Nativeint.shift_left 1n 16 in
+  {info with free_pages= Nativeint.sub info.free_pages emergency_reserve_pages}

ocaml/libs/xenctrl-ext/xenctrlext.mli

@@ -107,3 +107,5 @@ val domain_claim_pages : handle -> domid -> ?numa_node:NumaNode.t -> int -> unit
 
 val get_nr_nodes : handle -> int
 (** Returns the count of NUMA nodes available in the system. *)
+
+val physinfo : Xenctrl.handle -> Xenctrl.physinfo

ocaml/squeezed/src/squeeze_xen.ml

@@ -579,7 +579,7 @@ let make_host ~verbose ~xc =
      pages -- this might cause something else to fail (eg domain builder?) *)
   while
     Int64.div
-      ((Xenctrl.physinfo xc).Xenctrl.scrub_pages |> Int64.of_nativeint)
+      ((Xenctrlext.physinfo xc).Xenctrl.scrub_pages |> Int64.of_nativeint)
       1024L
     <> 0L
   do
@@ -762,7 +762,7 @@ let make_host ~verbose ~xc =
   (* For the host free memory we sum the free pages and the pages needing
      scrubbing: we don't want to adjust targets simply because the scrubber is
      slow. *)
-  let physinfo = Xenctrl.physinfo xc in
+  let physinfo = Xenctrlext.physinfo xc in
   let free_pages_kib =
     Xenctrl.pages_to_kib (Int64.of_nativeint physinfo.Xenctrl.free_pages)
   and scrub_pages_kib =

ocaml/xcp-rrdd/bin/rrdp-cpu/rrdp_cpu.ml

@@ -184,7 +184,7 @@ let dss_pcpus xc =
   let len = Array.length !physcpus in
   let newinfos =
     if len = 0 then (
-      let physinfo = Xenctrl.physinfo xc in
+      let physinfo = Xenctrlext.physinfo xc in
       let pcpus = physinfo.Xenctrl.nr_cpus in
       physcpus := if pcpus > 0 then Array.make pcpus 0L else [||] ;
       Xenctrl.pcpu_info xc pcpus
@@ -237,7 +237,7 @@ let count_power_state_running_domains domains =
     0 domains
 
 let dss_hostload xc domains =
-  let physinfo = Xenctrl.physinfo xc in
+  let physinfo = Xenctrlext.physinfo xc in
   let pcpus = physinfo.Xenctrl.nr_cpus in
   let rec sum acc n f =
     match n with n when n >= 0 -> sum (acc + f n) (n - 1) f | _ -> acc
@@ -298,7 +298,7 @@ let _ =
       let _, domains, _ = Xenctrl_lib.domain_snapshot xc in
       Process.initialise () ;
       (* Share one page per PCPU and dom each *)
-      let physinfo = Xenctrl.physinfo xc in
+      let physinfo = Xenctrlext.physinfo xc in
       let shared_page_count =
         physinfo.Xenctrl.nr_cpus
         + Int.max Rrd_interface.max_supported_vms (List.length domains)

ocaml/xcp-rrdd/bin/rrdp-squeezed/rrdp_squeezed.ml

@@ -169,7 +169,7 @@ let generate_host_sources xc counters =
   in
   let memory_reclaimed = bytes_of_kib memory_reclaimed in
   let memory_possibly_reclaimed = bytes_of_kib memory_possibly_reclaimed in
-  let physinfo = Xenctrl.physinfo xc in
+  let physinfo = Xenctrlext.physinfo xc in
   let total_kib =
     Xenctrl.pages_to_kib (Int64.of_nativeint physinfo.Xenctrl.total_pages)
   in

ocaml/xenopsd/xc/domain.ml

@@ -235,7 +235,7 @@ let wait_xen_free_mem ~xc ?(maximum_wait_time_seconds = 64) required_memory_kib
     : bool =
   let open Memory in
   let rec wait accumulated_wait_time_seconds =
-    let host_info = Xenctrl.physinfo xc in
+    let host_info = Xenctrlext.physinfo xc in
     let free_memory_kib =
       kib_of_pages (Int64.of_nativeint host_info.Xenctrl.free_pages)
     in
@@ -275,7 +275,7 @@ let wait_xen_free_mem ~xc ?(maximum_wait_time_seconds = 64) required_memory_kib
 let make ~xc ~xs vm_info vcpus domain_config uuid final_uuid no_sharept
     num_of_vbds num_of_vifs =
   let open Xenctrl in
-  let host_info = Xenctrl.physinfo xc in
+  let host_info = Xenctrlext.physinfo xc in
 
   (* Confirm that the running hypervisor supports a specific capability. *)
   let assert_capability cap ~on_error =

ocaml/xenopsd/xc/emu_manager.ml

@@ -205,7 +205,7 @@ let non_debug_receive ?debug_callback cnx =
         let open Memory in
         let open Int64 in
         let open Xenctrl in
-        let p = Xenctrl.physinfo xc in
+        let p = Xenctrlext.physinfo xc in
         error "Memory F %Ld KiB S %Ld KiB T %Ld MiB"
           (p.free_pages |> of_nativeint |> kib_of_pages)
           (p.scrub_pages |> of_nativeint |> kib_of_pages)

ocaml/xenopsd/xc/memory_breakdown.ml

@@ -217,7 +217,7 @@ let print_memory_field_names () =
 
 (** Prints memory field values to the console. *)
 let print_memory_field_values xc xs =
-  let host = Xenctrl.physinfo xc in
+  let host = Xenctrlext.physinfo xc in
   let control_domain_info = Xenctrl.domain_getinfo xc 0 in
   let control_domain_id = control_domain_info.Xenctrl.handle in
   let guests =