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src/hotspot/os/linux/os_linux.cpp

@@ -2139,7 +2139,7 @@ void os::Linux::print_system_memory_info(outputStream* st) {
 
 bool os::Linux::query_process_memory_info(os::Linux::meminfo_t* info) {
   FILE* f = ::fopen("/proc/self/status", "r");
-  const int num_values = 8;
+  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 =
@@ -2151,9 +2151,9 @@ bool os::Linux::query_process_memory_info(os::Linux::meminfo_t* info) {
            (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) ||
-           (info->rssfile == -1   && sscanf(buf, "RssFile: " SSIZE_FORMAT " kB", &info->rssfile) == 1) ||
-           (info->rssshmem == -1  && sscanf(buf, "RssShmem: " SSIZE_FORMAT " kB", &info->rssshmem) == 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 ++;

src/hotspot/os/linux/trimCHeapDCmd.cpp

@@ -36,9 +36,9 @@ void TrimCLibcHeapDCmd::execute(DCmdSource source, TRAPS) {
 #ifdef __GLIBC__
   stringStream ss_report(1024); // Note: before calling trim
 
-  // Query memory before...
   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...");
@@ -49,25 +49,30 @@ void TrimCLibcHeapDCmd::execute(DCmdSource source, TRAPS) {
   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;
     }
-  } else {
+  }
+  if (!wrote_something) {
     ss_report.print_raw("No details available.");
   }
+
   _output->print_raw(ss_report.base());
-  log_info(os)("malloc_trim: ");
-  log_info(os)("%s", 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

@@ -34,10 +34,10 @@ class TrimCLibcHeapDCmd : public DCmd {
 public:
   TrimCLibcHeapDCmd(outputStream* output, bool heap) : DCmd(output, heap) {}
   static const char* name() {
-    return "VM.trim_libc_heap";
+    return "System.glibc_trim_heap";
   }
   static const char* description() {
-    return "Attempts to free up memory by trimming the glibc heap.";
+    return "Attempts to free up memory by trimming the glibc C-heap.";
   }
   static const char* impact() {
     return "Low";

src/hotspot/share/services/diagnosticCommand.cpp

@@ -96,7 +96,6 @@ void DCmdRegistrant::register_dcmds(){
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<RunFinalizationDCmd>(full_export, true, false));
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<HeapInfoDCmd>(full_export, true, false));
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<FinalizerInfoDCmd>(full_export, true, false));
-  LINUX_ONLY(DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<TrimCLibcHeapDCmd>(full_export, true, false));)
 #if INCLUDE_SERVICES
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<HeapDumpDCmd>(DCmd_Source_Internal | DCmd_Source_AttachAPI, true, false));
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<ClassHistogramDCmd>(full_export, true, false));
@@ -121,6 +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

@@ -40,9 +40,12 @@
  */
 public class TrimLibcHeapTest {
     public void run(CommandExecutor executor) {
-        OutputAnalyzer output = executor.execute("VM.trim_libc_heap");
+        OutputAnalyzer output = executor.execute("System.glibc_trim_heap");
         output.reportDiagnosticSummary();
-        output.shouldMatch("(Done|Not available)");
+        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