Allow users to change the default vector growth stategy (#3389)

This allows users to set at runtime an alternate to the default vector
growth factor of 1.5. This could help save memory in simulations that
use a lot of particles and are close to the capacity of the GPU device.

The proposed changes:
- [ ] fix a bug or incorrect behavior in AMReX
- [x] add new capabilities to AMReX
- [ ] changes answers in the test suite to more than roundoff level
- [ ] are likely to significantly affect the results of downstream AMReX
users
- [ ] include documentation in the code and/or rst files, if appropriate

---------

Co-authored-by: Weiqun Zhang <WeiqunZhang@lbl.gov>

Src/Base/AMReX.cpp

@@ -604,6 +604,7 @@ amrex::Initialize (int& argc, char**& argv, bool build_parm_parse,
     iMultiFab::Initialize();
     VisMF::Initialize();
     AsyncOut::Initialize();
+    VectorGrowthStrategy::Initialize();
 
 #ifdef AMREX_USE_EB
     EB2::Initialize();

Src/Base/AMReX_PODVector.H

@@ -218,6 +218,14 @@ namespace amrex
         }
     }
 
+    namespace VectorGrowthStrategy
+    {
+        extern AMREX_EXPORT Real growth_factor;
+        inline Real GetGrowthFactor () { return growth_factor; }
+
+        void Initialize ();
+    }
+
     template <class T, class Allocator = std::allocator<T> >
     class PODVector : public Allocator
     {
@@ -612,7 +620,8 @@ namespace amrex
 
             while (new_capacity < (capacity() + a_num_to_be_added))
             {
-                new_capacity = (3 * new_capacity + 1)/2;
+                new_capacity = static_cast<size_type>(
+                    VectorGrowthStrategy::GetGrowthFactor() * static_cast<Real>(new_capacity + 1));
             }
 
             return new_capacity;

Src/Base/AMReX_PODVector.cpp

@@ -0,0 +1,33 @@
+#include <AMReX_PODVector.H>
+#include <AMReX_ParmParse.H>
+#include <AMReX_REAL.H>
+
+namespace amrex::VectorGrowthStrategy
+{
+    Real growth_factor = 1.5_rt;
+
+    void Initialize () {
+        ParmParse pp("amrex");
+        pp.queryAdd("vector_growth_factor", growth_factor);
+
+        // clamp user input to reasonable values
+        constexpr Real min_factor = 1.05_rt;
+        constexpr Real max_factor = 4._rt;
+
+        if (growth_factor < min_factor) {
+            if (Verbose()) {
+                amrex::Print() << "Warning: user-provided vector growth factor is too small."
+                               << " Clamping to " << min_factor << ". \n";
+            }
+            growth_factor = min_factor;
+        }
+
+        if (growth_factor > max_factor) {
+            if (Verbose()) {
+                amrex::Print() << "Warning: user-provided vector growth factor is too large."
+                               << " Clamping to " << max_factor << ". \n";
+            }
+            growth_factor = max_factor;
+        }
+    }
+}

Src/Base/CMakeLists.txt

@@ -25,6 +25,7 @@ foreach(D IN LISTS AMReX_SPACEDIM)
        AMReX_Exception.H
        AMReX_Extension.H
        AMReX_PODVector.H
+       AMReX_PODVector.cpp
        AMReX_ParmParse.cpp
        AMReX_parmparse_fi.cpp
        AMReX_ParmParse.H

Src/Base/Make.package

@@ -17,6 +17,7 @@ C$(AMREX_BASE)_headers += AMReX_Demangle.H AMReX_Extension.H
 C$(AMREX_BASE)_headers += AMReX_GpuComplex.H
 
 C$(AMREX_BASE)_headers += AMReX_PODVector.H
+C$(AMREX_BASE)_sources += AMReX_PODVector.cpp
 
 C$(AMREX_BASE)_headers += AMReX_BlockMutex.H
 C$(AMREX_BASE)_sources += AMReX_BlockMutex.cpp