# HG changeset patch
# User stuefe
# Date 1589451433 -7200
#      Thu May 14 12:17:13 2020 +0200
# Node ID 48755534c27f227d095ae3ebcc6f3911232950d2
# Parent  a44396903fd82fbed8eb97006669a397dfe32da6
[mq]: nmt-os-split-reserved-memory

diff -r a44396903fd8 -r 48755534c27f src/hotspot/share/services/memTracker.hpp
--- a/src/hotspot/share/services/memTracker.hpp	Thu May 14 08:48:36 2020 +0200
+++ b/src/hotspot/share/services/memTracker.hpp	Thu May 14 12:17:13 2020 +0200
@@ -240,6 +240,20 @@
     }
   }
 
+  // Given an existing memory mapping registered with NMT, split the mapping in two.
+  // This is called in the context of os::split_reserved_memory(..., realloc=true), so we do not have to care
+  //  about committed memory in the unsplit region (we can treat this as a release, followed by two independent reserve operations).
+  // The newly created two mappings will be registered under the call stack and the memory flags of the original section.
+  static inline void record_virtual_memory_split_reserved(void* addr, size_t size, size_t split) {
+    if (tracking_level() < NMT_summary) return;
+    if (addr != NULL) {
+      ThreadCritical tc;
+      // Recheck to avoid potential racing during NMT shutdown
+      if (tracking_level() < NMT_summary) return;
+      VirtualMemoryTracker::split_reserved_region((address)addr, size, split);
+    }
+  }
+
   static inline void record_virtual_memory_type(void* addr, MEMFLAGS flag) {
     if (tracking_level() < NMT_summary) return;
     if (addr != NULL) {
diff -r a44396903fd8 -r 48755534c27f src/hotspot/share/services/virtualMemoryTracker.cpp
--- a/src/hotspot/share/services/virtualMemoryTracker.cpp	Thu May 14 08:48:36 2020 +0200
+++ b/src/hotspot/share/services/virtualMemoryTracker.cpp	Thu May 14 12:17:13 2020 +0200
@@ -490,6 +490,32 @@
   }
 }
 
+// Given an existing memory mapping registered with NMT, split the mapping in two.
+// The newly created two mappings will be registered under the call stack and the memory flags of the original section.
+bool VirtualMemoryTracker::split_reserved_region(address addr, size_t size, size_t split) {
+
+  ReservedMemoryRegion  rgn(addr, size);
+  ReservedMemoryRegion* reserved_rgn = _reserved_regions->find(rgn);
+  assert(reserved_rgn != NULL, "No reserved region");
+
+  // Squirrel away the old region flags and stack for later.
+  MEMFLAGS flags = reserved_rgn->flag();
+  NativeCallStack stack = *reserved_rgn->call_stack();
+
+  // The original region must be completely uncommitted.
+  assert(reserved_rgn->committed_size() == 0, "Splitting committed region?");
+
+  // Remove the region.
+  _reserved_regions->remove(rgn);
+
+  // Now, create two new regions.
+  add_reserved_region(addr, split, stack, flags);
+  add_reserved_region(addr + split, size - split, stack, flags);
+
+  return true;
+}
+
+
 // Iterate the range, find committed region within its bound.
 class RegionIterator : public StackObj {
 private:
diff -r a44396903fd8 -r 48755534c27f src/hotspot/share/services/virtualMemoryTracker.hpp
--- a/src/hotspot/share/services/virtualMemoryTracker.hpp	Thu May 14 08:48:36 2020 +0200
+++ b/src/hotspot/share/services/virtualMemoryTracker.hpp	Thu May 14 12:17:13 2020 +0200
@@ -405,6 +405,10 @@
   static bool remove_released_region    (address base_addr, size_t size);
   static void set_reserved_region_type  (address addr, MEMFLAGS flag);
 
+  // Given an existing memory mapping registered with NMT, split the mapping in two.
+  // The newly created two mappings will be registered under the call stack and the memory flags of the original section.
+  static bool split_reserved_region(address addr, size_t size, size_t split);
+
   // Walk virtual memory data structure for creating baseline, etc.
   static bool walk_virtual_memory(VirtualMemoryWalker* walker);