diff --git a/Dockerfile b/Dockerfile
index 43d1adb..c09868d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -2,14 +2,14 @@
 # It will probably still work on newer images, though, unless Debian
 # changes some compiler optimisations (unlikely).
 #FROM ocurrent/opam:alpine-3.10-ocaml-4.10
-FROM ocurrent/opam@sha256:d30098ff92b5ee10cf7c11c17f2351705e5226a6b05aa8b9b7280b3d87af9cde
+FROM ocurrent/opam@sha256:4546b41a99b54f163af435327c86f88d06346f2a059f0f42bea431b37329ea8d
 
 # Pin last known-good version for reproducible builds.
 # Remove this line (and the base image pin above) if you want to test with the
 # latest versions.
-RUN cd ~/opam-repository && git fetch origin master && git reset --hard e81ab2996896b21cba74c43a903b305a5a6341ef && opam update
+RUN cd ~/opam-repository && git fetch origin master && git reset --hard 6ef290f5681b7ece5d9c085bcf0c55268c118292 && opam update
 
-RUN opam depext -i -y mirage.3.8.0 lwt.5.3.0
+RUN opam depext -i -y mirage
 RUN mkdir /home/opam/qubes-mirage-firewall
 ADD config.ml /home/opam/qubes-mirage-firewall/config.ml
 WORKDIR /home/opam/qubes-mirage-firewall
diff --git a/build-with-docker.sh b/build-with-docker.sh
index 9820d15..ed8e5e6 100755
--- a/build-with-docker.sh
+++ b/build-with-docker.sh
@@ -5,5 +5,5 @@ docker build -t qubes-mirage-firewall .
 echo Building Firewall...
 docker run --rm -i -v `pwd`:/home/opam/qubes-mirage-firewall qubes-mirage-firewall
 echo "SHA2 of build:   $(sha256sum qubes_firewall.xen)"
-echo "SHA2 last known: 0f6b41fa3995afccff1809cb893c45c0863477d4dfacc441c11e3382bec31d39"
+echo "SHA2 last known: a635ead410ffb72abb8b44e8c5f8f2cfc8752c4787e737ed6cdc0089143ace00"
 echo "(hashes should match for released versions)"
diff --git a/config.ml b/config.ml
index 3075006..fb2cd2e 100644
--- a/config.ml
+++ b/config.ml
@@ -33,7 +33,7 @@ let main =
       package "mirage-qubes" ~min:"0.8.2";
       package "mirage-nat" ~min:"2.2.1";
       package "mirage-logs";
-      package "mirage-xen" ~min:"5.0.0";
+      package "mirage-xen" ~min:"6.0.0";
       package ~min:"4.5.0" "dns-client";
       package "pf-qubes";
     ]
diff --git a/memory_pressure.ml b/memory_pressure.ml
index ed5b7e5..cecf4a9 100644
--- a/memory_pressure.ml
+++ b/memory_pressure.ml
@@ -6,44 +6,48 @@ open Lwt
 let src = Logs.Src.create "memory_pressure" ~doc:"Memory pressure monitor"
 module Log = (val Logs.src_log src : Logs.LOG)
 
-let total_pages = OS.MM.Heap_pages.total ()
-let pagesize_kb = Io_page.page_size / 1024
+let wordsize_in_bytes = Sys.word_size / 8
 
-let meminfo ~used =
-  let mem_total = total_pages * pagesize_kb in
-  let mem_free = (total_pages - used) * pagesize_kb in
-  Log.info (fun f -> f "Writing meminfo: free %d / %d kB (%.2f %%)"
-    mem_free mem_total (float_of_int mem_free /. float_of_int mem_total *. 100.0));
+let fraction_free stats =
+  let { OS.Memory.free_words; heap_words; _ } = stats in
+  float free_words /. float heap_words
+
+let meminfo stats =
+  let { OS.Memory.free_words; heap_words; _ } = stats in
+  let mem_total = heap_words * wordsize_in_bytes in
+  let mem_free = free_words * wordsize_in_bytes in
+  Log.info (fun f -> f "Writing meminfo: free %a / %a (%.2f %%)"
+    Fmt.bi_byte_size mem_free
+    Fmt.bi_byte_size mem_total
+    (fraction_free stats *. 100.0));
   Printf.sprintf "MemTotal: %d kB\n\
                   MemFree: %d kB\n\
                   Buffers: 0 kB\n\
                   Cached: 0 kB\n\
                   SwapTotal: 0 kB\n\
-                  SwapFree: 0 kB\n" mem_total mem_free
+                  SwapFree: 0 kB\n" (mem_total / 1024) (mem_free / 1024)
 
-let report_mem_usage used =
+let report_mem_usage stats =
   Lwt.async (fun () ->
     let open OS in
     Xs.make () >>= fun xs ->
     Xs.immediate xs (fun h ->
-      Xs.write h "memory/meminfo" (meminfo ~used)
+      Xs.write h "memory/meminfo" (meminfo stats)
     )
   )
 
 let init () =
   Gc.full_major ();
-  let used = OS.MM.Heap_pages.used () in
-  report_mem_usage used
+  let stats = OS.Memory.quick_stat () in
+  report_mem_usage stats
 
 let status () =
-  let used = OS.MM.Heap_pages.used () |> float_of_int in
-  let frac = used /. float_of_int total_pages in
-  if frac < 0.9 then `Ok
+  let stats = OS.Memory.quick_stat () in
+  if fraction_free stats > 0.1 then `Ok
   else (
     Gc.full_major ();
-    let used = OS.MM.Heap_pages.used () in
-    report_mem_usage used;
-    let frac = float_of_int used /. float_of_int total_pages in
-    if frac > 0.9 then `Memory_critical
+    let stats = OS.Memory.quick_stat () in
+    report_mem_usage stats;
+    if fraction_free stats < 0.1 then `Memory_critical
     else `Ok
   )