--- a/src/hotspot/share/logging/logLevel.cpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/src/hotspot/share/logging/logLevel.cpp	Mon Feb 26 09:34:20 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -24,6 +24,7 @@
 #include "precompiled.hpp"
 #include "logging/logLevel.hpp"
 #include "utilities/globalDefinitions.hpp"
+#include "utilities/stringUtils.hpp"
 
 const char* LogLevel::_name[] = {
   "off",
@@ -40,3 +41,19 @@
   }
   return Invalid;
 }
+
+LogLevelType LogLevel::fuzzy_match(const char *level) {
+  size_t len = strlen(level);
+  LogLevelType match = LogLevel::Invalid;
+  double best = 0.4; // required similarity to be considered a match
+  for (uint i = 1; i < Count; i++) {
+    LogLevelType cur = static_cast<LogLevelType>(i);
+    const char* levelname = LogLevel::name(cur);
+    double score = StringUtils::similarity(level, len, levelname, strlen(levelname));
+    if (score >= best) {
+      match = cur;
+      best= score;
+    }
+  }
+  return match;
+}

--- a/src/hotspot/share/logging/logLevel.hpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/src/hotspot/share/logging/logLevel.hpp	Mon Feb 26 09:34:20 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -71,6 +71,7 @@
   }
 
   static LogLevel::type from_string(const char* str);
+  static LogLevel::type fuzzy_match(const char *level);
 
  private:
   static const char* _name[];

--- a/src/hotspot/share/logging/logSelection.cpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/src/hotspot/share/logging/logSelection.cpp	Mon Feb 26 09:34:20 2018 +0100
@@ -72,10 +72,16 @@
   LogLevelType level = LogLevel::Unspecified;
   char* equals = strchr(str, '=');
   if (equals != NULL) {
-    level = LogLevel::from_string(equals + 1);
+    const char* levelstr = equals + 1;
+    level = LogLevel::from_string(levelstr);
     if (level == LogLevel::Invalid) {
       if (errstream != NULL) {
-        errstream->print_cr("Invalid level '%s' in log selection.", equals + 1);
+        errstream->print("Invalid level '%s' in log selection.", levelstr);
+        LogLevelType match = LogLevel::fuzzy_match(levelstr);
+        if (match != LogLevel::Invalid) {
+          errstream->print(" Did you mean '%s'?", LogLevel::name(match));
+        }
+        errstream->cr();
       }
       return LogSelection::Invalid;
     }
@@ -109,7 +115,12 @@
     LogTagType tag = LogTag::from_string(cur_tag);
     if (tag == LogTag::__NO_TAG) {
       if (errstream != NULL) {
-        errstream->print_cr("Invalid tag '%s' in log selection.", cur_tag);
+        errstream->print("Invalid tag '%s' in log selection.", cur_tag);
+        LogTagType match =  LogTag::fuzzy_match(cur_tag);
+        if (match != LogTag::__NO_TAG) {
+          errstream->print(" Did you mean '%s'?", LogTag::name(match));
+        }
+        errstream->cr();
       }
       return LogSelection::Invalid;
     }

--- a/src/hotspot/share/logging/logTag.cpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/src/hotspot/share/logging/logTag.cpp	Mon Feb 26 09:34:20 2018 +0100
@@ -23,6 +23,7 @@
  */
 #include "precompiled.hpp"
 #include "logging/logTag.hpp"
+#include "utilities/stringUtils.hpp"
 #include "utilities/globalDefinitions.hpp"
 #include "utilities/ostream.hpp"
 #include "utilities/quickSort.hpp"
@@ -43,6 +44,22 @@
   return __NO_TAG;
 }
 
+LogTagType LogTag::fuzzy_match(const char *str) {
+  size_t len = strlen(str);
+  LogTagType match = LogTag::__NO_TAG;
+  double best = 0.5; // required similarity to be considered a match
+  for (size_t i = 1; i < LogTag::Count; i++) {
+    LogTagType tag = static_cast<LogTagType>(i);
+    const char* tagname = LogTag::name(tag);
+    double score = StringUtils::similarity(tagname, strlen(tagname), str, len);
+    if (score >= best) {
+      match = tag;
+      best = score;
+    }
+  }
+  return match;
+}
+
 static int cmp_logtag(LogTagType a, LogTagType b) {
   return strcmp(LogTag::name(a), LogTag::name(b));
 }

--- a/src/hotspot/share/logging/logTag.hpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/src/hotspot/share/logging/logTag.hpp	Mon Feb 26 09:34:20 2018 +0100
@@ -192,6 +192,7 @@
   }
 
   static LogTag::type from_string(const char *str);
+  static LogTag::type fuzzy_match(const char *tag);
   static void list_tags(outputStream* out);
 
  private:

--- a/src/hotspot/share/runtime/globals.cpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/src/hotspot/share/runtime/globals.cpp	Mon Feb 26 09:34:20 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -38,6 +38,7 @@
 #include "utilities/defaultStream.hpp"
 #include "utilities/macros.hpp"
 #include "utilities/ostream.hpp"
+#include "utilities/stringUtils.hpp"
 #if INCLUDE_ALL_GCS
 #include "gc/g1/g1_globals.hpp"
 #endif // INCLUDE_ALL_GCS
@@ -880,25 +881,6 @@
   return _name_len;
 }
 
-// Compute string similarity based on Dice's coefficient
-static float str_similar(const char* str1, const char* str2, size_t len2) {
-  int len1 = (int) strlen(str1);
-  int total = len1 + (int) len2;
-
-  int hit = 0;
-
-  for (int i = 0; i < len1 -1; ++i) {
-    for (int j = 0; j < (int) len2 -1; ++j) {
-      if ((str1[i] == str2[j]) && (str1[i+1] == str2[j+1])) {
-        ++hit;
-        break;
-      }
-    }
-  }
-
-  return 2.0f * (float) hit / (float) total;
-}
-
 Flag* Flag::fuzzy_match(const char* name, size_t length, bool allow_locked) {
   float VMOptionsFuzzyMatchSimilarity = 0.7f;
   Flag* match = NULL;
@@ -906,7 +888,7 @@
   float max_score = -1;
 
   for (Flag* current = &flagTable[0]; current->_name != NULL; current++) {
-    score = str_similar(current->_name, name, length);
+    score = StringUtils::similarity(current->_name, strlen(current->_name), name, length);
     if (score > max_score) {
       max_score = score;
       match = current;

--- a/src/hotspot/share/utilities/stringUtils.cpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/src/hotspot/share/utilities/stringUtils.cpp	Mon Feb 26 09:34:20 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -41,3 +41,19 @@
 
   return replace_count;
 }
+
+double StringUtils::similarity(const char* str1, size_t len1, const char* str2, size_t len2) {
+  size_t total = len1 + len2;
+
+  size_t hit = 0;
+  for (size_t i = 0; i < len1 - 1; i++) {
+    for (size_t j = 0; j < len2 - 1; j++) {
+      if ((str1[i] == str2[j]) && (str1[i+1] == str2[j+1])) {
+        ++hit;
+        break;
+      }
+    }
+  }
+
+  return 2.0 * (double) hit / (double) total;
+}

--- a/src/hotspot/share/utilities/stringUtils.hpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/src/hotspot/share/utilities/stringUtils.hpp	Mon Feb 26 09:34:20 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -37,6 +37,9 @@
   //
   // Returns the count of substrings that have been replaced.
   static int replace_no_expand(char* string, const char* from, const char* to);
+
+  // Compute string similarity based on Dice's coefficient
+  static double similarity(const char* str1, size_t len1, const char* str2, size_t len2);
 };
 
 #endif // SHARE_VM_UTILITIES_STRINGUTILS_HPP

--- a/test/hotspot/gtest/logging/test_logLevel.cpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/test/hotspot/gtest/logging/test_logLevel.cpp	Mon Feb 26 09:34:20 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -45,6 +45,18 @@
   EXPECT_EQ(LogLevel::Invalid, LogLevel::from_string("infodebugwarning"));
 }
 
+TEST(LogLevel, fuzzy_match) {
+  for (size_t i = 1; i < LogLevel::Count; i++) {
+    LogLevelType level = static_cast<LogLevelType>(i);
+    ASSERT_EQ(level, LogLevel::fuzzy_match(LogLevel::name(level)));
+  }
+
+  ASSERT_EQ(LogLevel::Warning, LogLevel::fuzzy_match("warn"));
+  ASSERT_EQ(LogLevel::Error, LogLevel::fuzzy_match("err"));
+
+  ASSERT_EQ(LogLevel::Invalid, LogLevel::fuzzy_match("unknown"));
+}
+
 TEST(LogLevel, name) {
   // Use names from macro as reference
 #define LOG_LEVEL(lname, lstring) \

--- a/test/hotspot/gtest/logging/test_logTag.cpp	Sat Feb 24 22:42:37 2018 -0800
+++ b/test/hotspot/gtest/logging/test_logTag.cpp	Mon Feb 26 09:34:20 2018 +0100
@@ -45,6 +45,18 @@
   }
 }
 
+TEST(LogTag, fuzzy_match) {
+  for (size_t i = 1; i < LogTag::Count; i++) {
+    LogTagType tag = static_cast<LogTagType>(i);
+    EXPECT_EQ(tag, LogTag::fuzzy_match(LogTag::name(tag)));
+  }
+
+  EXPECT_EQ(LogTag::_logging, LogTag::fuzzy_match("loggin"));
+  EXPECT_EQ(LogTag::_logging, LogTag::fuzzy_match("loging"));
+
+  EXPECT_EQ(LogTag::__NO_TAG, LogTag::fuzzy_match("unrecognizabletag"));
+}
+
 TEST(LogTag, name) {
   // Verify for each tag from the macro
 #define LOG_TAG(tag) \

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/gtest/utilities/test_stringUtils.cpp	Mon Feb 26 09:34:20 2018 +0100
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "utilities/stringUtils.hpp"
+#include "unittest.hpp"
+
+TEST(StringUtils, similarity) {
+  const char* str1 = "the quick brown fox jumps over the lazy dog";
+  const char* str2 = "the quick brown fox jumps over the lazy doh";
+  EXPECT_NEAR(0.95349, StringUtils::similarity(str1, strlen(str1), str2, strlen(str2)), 1e-5);
+}