JDK-8268893: jcmd to trim the glibc heap

src/hotspot/os/linux/os_linux.cpp

@@ -2137,44 +2137,51 @@ void os::Linux::print_system_memory_info(outputStream* st) {
                       "/sys/kernel/mm/transparent_hugepage/defrag", st);
 }
 
-void os::Linux::print_process_memory_info(outputStream* st) {
-
-  st->print_cr("Process Memory:");
-
-  // Print virtual and resident set size; peak values; swap; and for
-  //  rss its components if the kernel is recent enough.
-  ssize_t vmsize = -1, vmpeak = -1, vmswap = -1,
-      vmrss = -1, vmhwm = -1, rssanon = -1, rssfile = -1, rssshmem = -1;
-  const int num_values = 8;
-  int num_found = 0;
+bool os::Linux::query_process_memory_info(os::Linux::meminfo_t* info) {
   FILE* f = ::fopen("/proc/self/status", "r");
+  const int num_values = sizeof(os::Linux::meminfo_t) / sizeof(size_t);
+  int num_found = 0;
   char buf[256];
+  info->vmsize = info->vmpeak = info->vmrss = info->vmhwm = info->vmswap =
+      info->rssanon = info->rssfile = info->rssshmem = -1;
   if (f != NULL) {
     while (::fgets(buf, sizeof(buf), f) != NULL && num_found < num_values) {
-      if ( (vmsize == -1    && sscanf(buf, "VmSize: " SSIZE_FORMAT " kB", &vmsize) == 1) ||
-           (vmpeak == -1    && sscanf(buf, "VmPeak: " SSIZE_FORMAT " kB", &vmpeak) == 1) ||
-           (vmswap == -1    && sscanf(buf, "VmSwap: " SSIZE_FORMAT " kB", &vmswap) == 1) ||
-           (vmhwm == -1     && sscanf(buf, "VmHWM: " SSIZE_FORMAT " kB", &vmhwm) == 1) ||
-           (vmrss == -1     && sscanf(buf, "VmRSS: " SSIZE_FORMAT " kB", &vmrss) == 1) ||
-           (rssanon == -1   && sscanf(buf, "RssAnon: " SSIZE_FORMAT " kB", &rssanon) == 1) ||
-           (rssfile == -1   && sscanf(buf, "RssFile: " SSIZE_FORMAT " kB", &rssfile) == 1) ||
-           (rssshmem == -1  && sscanf(buf, "RssShmem: " SSIZE_FORMAT " kB", &rssshmem) == 1)
+      if ( (info->vmsize == -1    && sscanf(buf, "VmSize: " SSIZE_FORMAT " kB", &info->vmsize) == 1) ||
+           (info->vmpeak == -1    && sscanf(buf, "VmPeak: " SSIZE_FORMAT " kB", &info->vmpeak) == 1) ||
+           (info->vmswap == -1    && sscanf(buf, "VmSwap: " SSIZE_FORMAT " kB", &info->vmswap) == 1) ||
+           (info->vmhwm == -1     && sscanf(buf, "VmHWM: " SSIZE_FORMAT " kB", &info->vmhwm) == 1) ||
+           (info->vmrss == -1     && sscanf(buf, "VmRSS: " SSIZE_FORMAT " kB", &info->vmrss) == 1) ||
+           (info->rssanon == -1   && sscanf(buf, "RssAnon: " SSIZE_FORMAT " kB", &info->rssanon) == 1) || // Needs Linux 4.5
+           (info->rssfile == -1   && sscanf(buf, "RssFile: " SSIZE_FORMAT " kB", &info->rssfile) == 1) || // Needs Linux 4.5
+           (info->rssshmem == -1  && sscanf(buf, "RssShmem: " SSIZE_FORMAT " kB", &info->rssshmem) == 1)  // Needs Linux 4.5
            )
       {
         num_found ++;
       }
     }
     fclose(f);
+    return true;
+  }
+  return false;
+}
+
+void os::Linux::print_process_memory_info(outputStream* st) {
 
-    st->print_cr("Virtual Size: " SSIZE_FORMAT "K (peak: " SSIZE_FORMAT "K)", vmsize, vmpeak);
-    st->print("Resident Set Size: " SSIZE_FORMAT "K (peak: " SSIZE_FORMAT "K)", vmrss, vmhwm);
-    if (rssanon != -1) { // requires kernel >= 4.5
+  st->print_cr("Process Memory:");
+
+  // Print virtual and resident set size; peak values; swap; and for
+  //  rss its components if the kernel is recent enough.
+  meminfo_t info;
+  if (query_process_memory_info(&info)) {
+    st->print_cr("Virtual Size: " SSIZE_FORMAT "K (peak: " SSIZE_FORMAT "K)", info.vmsize, info.vmpeak);
+    st->print("Resident Set Size: " SSIZE_FORMAT "K (peak: " SSIZE_FORMAT "K)", info.vmrss, info.vmhwm);
+    if (info.rssanon != -1) { // requires kernel >= 4.5
       st->print(" (anon: " SSIZE_FORMAT "K, file: " SSIZE_FORMAT "K, shmem: " SSIZE_FORMAT "K)",
-                  rssanon, rssfile, rssshmem);
+                info.rssanon, info.rssfile, info.rssshmem);
     }
     st->cr();
-    if (vmswap != -1) { // requires kernel >= 2.6.34
-      st->print_cr("Swapped out: " SSIZE_FORMAT "K", vmswap);
+    if (info.vmswap != -1) { // requires kernel >= 2.6.34
+      st->print_cr("Swapped out: " SSIZE_FORMAT "K", info.vmswap);
     }
   } else {
     st->print_cr("Could not open /proc/self/status to get process memory related information");
@@ -2195,7 +2202,7 @@ void os::Linux::print_process_memory_info(outputStream* st) {
     struct glibc_mallinfo mi = _mallinfo();
     total_allocated = (size_t)(unsigned)mi.uordblks;
     // Since mallinfo members are int, glibc values may have wrapped. Warn about this.
-    might_have_wrapped = (vmrss * K) > UINT_MAX && (vmrss * K) > (total_allocated + UINT_MAX);
+    might_have_wrapped = (info.vmrss * K) > UINT_MAX && (info.vmrss * K) > (total_allocated + UINT_MAX);
   }
   if (_mallinfo2 != NULL || _mallinfo != NULL) {
     st->print_cr("C-Heap outstanding allocations: " SIZE_FORMAT "K%s",

src/hotspot/os/linux/os_linux.hpp

@@ -174,6 +174,23 @@ class Linux {
   // Return the namespace pid if so, otherwise -1.
   static int get_namespace_pid(int vmid);
 
+  // Output structure for query_process_memory_info()
+  struct meminfo_t {
+    ssize_t vmsize;     // current virtual size
+    ssize_t vmpeak;     // peak virtual size
+    ssize_t vmrss;      // current resident set size
+    ssize_t vmhwm;      // peak resident set size
+    ssize_t vmswap;     // swapped out
+    ssize_t rssanon;    // resident set size (anonymous mappings, needs 4.5)
+    ssize_t rssfile;    // resident set size (file mappings, needs 4.5)
+    ssize_t rssshmem;   // resident set size (shared mappings, needs 4.5)
+  };
+
+  // Attempts to query memory information about the current process and return it in the output structure.
+  // May fail (returns false) or succeed (returns true) but not all output fields are available; unavailable
+  // fields will contain -1.
+  static bool query_process_memory_info(meminfo_t* info);
+
   // Stack repair handling
 
   // none present

src/hotspot/os/linux/trimCHeapDCmd.cpp

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2021 SAP SE. All rights reserved.
+ * Copyright (c) 2021, 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 "logging/log.hpp"
+#include "runtime/os.hpp"
+#include "utilities/debug.hpp"
+#include "utilities/ostream.hpp"
+#include "trimCHeapDCmd.hpp"
+
+#include <malloc.h>
+
+void TrimCLibcHeapDCmd::execute(DCmdSource source, TRAPS) {
+#ifdef __GLIBC__
+  stringStream ss_report(1024); // Note: before calling trim
+
+  os::Linux::meminfo_t info1;
+  os::Linux::meminfo_t info2;
+  // Query memory before...
+  bool have_info1 = os::Linux::query_process_memory_info(&info1);
+
+  _output->print_cr("Attempting trim...");
+  ::malloc_trim(0);
+  _output->print_cr("Done.");
+
+  // ...and after trim.
+  bool have_info2 = os::Linux::query_process_memory_info(&info2);
+
+  // Print report both to output stream as well to UL
+  bool wrote_something = false;
+  if (have_info1 && have_info2) {
+    if (info1.vmsize != -1 && info2.vmsize != -1) {
+      ss_report.print_cr("Virtual size before: " SSIZE_FORMAT "k, after: " SSIZE_FORMAT "k, (" SSIZE_FORMAT "k)",
+                         info1.vmsize, info2.vmsize, (info2.vmsize - info1.vmsize));
+      wrote_something = true;
+    }
+    if (info1.vmrss != -1 && info2.vmrss != -1) {
+      ss_report.print_cr("RSS before: " SSIZE_FORMAT "k, after: " SSIZE_FORMAT "k, (" SSIZE_FORMAT "k)",
+                         info1.vmrss, info2.vmrss, (info2.vmrss - info1.vmrss));
+      wrote_something = true;
+    }
+    if (info1.vmswap != -1 && info2.vmswap != -1) {
+      ss_report.print_cr("Swap before: " SSIZE_FORMAT "k, after: " SSIZE_FORMAT "k, (" SSIZE_FORMAT "k)",
+                         info1.vmswap, info2.vmswap, (info2.vmswap - info1.vmswap));
+      wrote_something = true;
+    }
+  }
+  if (!wrote_something) {
+    ss_report.print_raw("No details available.");
+  }
+
+  _output->print_raw(ss_report.base());
+  log_info(os)("malloc_trim:\n%s", ss_report.base());
+#else
+  _output->print_cr("Not available.");
+#endif
+}

src/hotspot/os/linux/trimCHeapDCmd.hpp

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2021 SAP SE. All rights reserved.
+ * Copyright (c) 2021, 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.
+ *
+ */
+
+#ifndef OS_LINUX_TRIMCHEAPDCMD_HPP
+#define OS_LINUX_TRIMCHEAPDCMD_HPP
+
+#include "services/diagnosticCommand.hpp"
+
+class outputStream;
+
+class TrimCLibcHeapDCmd : public DCmd {
+public:
+  TrimCLibcHeapDCmd(outputStream* output, bool heap) : DCmd(output, heap) {}
+  static const char* name() {
+    return "System.trim_native_heap";
+  }
+  static const char* description() {
+    return "Attempts to free up memory by trimming the C-heap.";
+  }
+  static const char* impact() {
+    return "Low";
+  }
+  static const JavaPermission permission() {
+    JavaPermission p = { "java.lang.management.ManagementPermission", "control", NULL };
+    return p;
+  }
+  virtual void execute(DCmdSource source, TRAPS);
+};
+
+#endif // OS_LINUX_TRIMCHEAPDCMD_HPP

src/hotspot/share/services/diagnosticCommand.cpp

@@ -58,7 +58,9 @@
 #include "utilities/events.hpp"
 #include "utilities/formatBuffer.hpp"
 #include "utilities/macros.hpp"
-
+#ifdef LINUX
+#include "trimCHeapDCmd.hpp"
+#endif
 
 static void loadAgentModule(TRAPS) {
   ResourceMark rm(THREAD);
@@ -118,6 +120,7 @@ void DCmdRegistrant::register_dcmds(){
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<CodeCacheDCmd>(full_export, true, false));
 #ifdef LINUX
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<PerfMapDCmd>(full_export, true, false));
+  DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<TrimCLibcHeapDCmd>(full_export, true, false));
 #endif // LINUX
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<TouchedMethodsDCmd>(full_export, true, false));
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<CodeHeapAnalyticsDCmd>(full_export, true, false));

test/hotspot/jtreg/serviceability/dcmd/vm/TrimLibcHeapTest.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2021 SAP SE. All rights reserved.
+ * Copyright (c) 2021, 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.
+ */
+
+import org.testng.annotations.Test;
+import jdk.test.lib.dcmd.CommandExecutor;
+import jdk.test.lib.dcmd.JMXExecutor;
+import jdk.test.lib.process.OutputAnalyzer;
+
+/*
+ * @test
+ * @summary Test of diagnostic command VM.trim_libc_heap
+ * @library /test/lib
+ * @requires os.family == "linux"
+ * @modules java.base/jdk.internal.misc
+ *          java.compiler
+ *          java.management
+ *          jdk.internal.jvmstat/sun.jvmstat.monitor
+ * @run testng TrimLibcHeapTest
+ */
+public class TrimLibcHeapTest {
+    public void run(CommandExecutor executor) {
+        OutputAnalyzer output = executor.execute("System.trim_native_heap");
+        output.reportDiagnosticSummary();
+        output.shouldMatch("(Done|Not available)"); // Not available could happen on Linux + non-glibc (eg. muslc)
+        if (output.firstMatch("Done") != null) {
+            output.shouldMatch("(Virtual size before|RSS before|Swap before|No details available)");
+        }
+    }
+
+    @Test
+    public void jmx() {
+        run(new JMXExecutor());
+    }
+}