diff -r 000000000000 -r 6474c204b198 tools/trace-malloc/histogram-diff.sh
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tools/trace-malloc/histogram-diff.sh	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,76 @@
+#!/bin/sh
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#   histogram-diff.sh [-c <count>] <base> <incr>
+#
+# Compute incremental memory growth from histogram in file <base> to
+# histogram in file <incr>, displaying at most <count> rows.
+
+# How many rows are we gonna show?
+COUNT=20
+
+# Read arguments
+while [ $# -gt 0 ]; do
+    case "$1" in
+    -c) COUNT=$2
+        shift 2
+        ;;
+    *)  break
+        ;;
+    esac
+done
+
+BASE=$1
+INCR=$2
+
+# Sort the base and incremental files so that we can `join' them on
+# the type name
+sort $BASE > /tmp/$$.left
+sort $INCR > /tmp/$$.right
+
+# Do the join. The `awk' script computes the difference between
+# the base and the incremental files.
+join /tmp/$$.left /tmp/$$.right \
+    | awk '{ print $1, $2, $3, $4, $5, $4 - $2, $5 - $3; }' \
+    > /tmp/$$.joined
+
+rm -f /tmp/$$.left /tmp/$$.right
+
+# Now compute a `TOTAL' row.
+awk '{ tobj1 += $2; tbytes1 += $3; tobj2 += $4; tbytes2 += $5; tdobj += $6; tdbytes += $7; } END { print "TOTAL", tobj1, tbytes1, tobj2, tbytes2, tdobj, tdbytes; }' /tmp/$$.joined \
+    > /tmp/$$.sorted
+
+# Then, we sort by the largest delta in bytes.
+sort -nr +6 /tmp/$$.joined >> /tmp/$$.sorted
+
+rm -f /tmp/$$.joined
+
+# Pretty-print, including percentages
+cat <<EOF > /tmp/$$.awk
+BEGIN {
+  print "                        ---- Base ----   ---- Incr ----   ----- Difference ----";
+  print "Type                    Count    Bytes   Count    Bytes   Count    Bytes %Total";
+  }
+\$1 == "TOTAL" {
+  tbytes = \$7;
+  }
+NR <= $COUNT {
+  printf "%-22s %6d %8d  %6d %8d  %6d %8d %6.2lf\n", \$1, \$2, \$3, \$4, \$5, \$6, \$7, 100.0 * \$7 / tbytes;
+  }
+NR > $COUNT {
+  oobjs1 += \$2;  obytes1 += \$3;
+  oobjs2 += \$4;  obytes2 += \$5;
+  odobjs += \$6;  odbytes += \$7;
+  }
+END {
+  printf "%-22s %6d %8d  %6d %8d  %6d %8d %6.2lf\n", "OTHER", oobjs1, obytes1, oobjs2, obytes2, odobjs, odbytes, odbytes * 100.0 / tbytes;
+  }
+EOF
+
+# Now pretty print the file, and spit it out on stdout.
+awk -f /tmp/$$.awk /tmp/$$.sorted
+
+rm -f /tmp/$$.awk /tmp/$$.sorted