diff --git a/include/xo/alloc/ArenaAlloc.hpp b/include/xo/alloc/ArenaAlloc.hpp
index 64546cf3..66dd6a70 100644
--- a/include/xo/alloc/ArenaAlloc.hpp
+++ b/include/xo/alloc/ArenaAlloc.hpp
@@ -36,9 +36,24 @@ namespace xo {
                                        std::size_t z,
                                        bool debug_flag);
 
+            /** size of virtual address range reserved for this allocator **/
+            std::size_t reserved() const { return this->size(); }
+
+            std::size_t page_size() const { return page_z_; }
             std::byte * free_ptr() const { return free_ptr_; }
             void       set_free_ptr(std::byte * x);
 
+            /** if address @p x is allocated from this arena,
+             *  return true along with offset relative to base address @ref lo_
+             *  otherwise return false with 0
+             **/
+            std::pair<bool, std::size_t> location_of(const void * x) const;
+
+            /** allocated span **/
+            std::pair<const std::byte *, const std::byte *> allocated_span() const {
+                return std::make_pair(lo_, free_ptr_);
+            }
+
             /** Reset to empty state **/
             void reset(std::size_t /*z_ignored*/) { this->clear(); }
 
diff --git a/include/xo/alloc/GC.hpp b/include/xo/alloc/GC.hpp
index a653b54b..ab58b902 100644
--- a/include/xo/alloc/GC.hpp
+++ b/include/xo/alloc/GC.hpp
@@ -50,6 +50,8 @@ namespace xo {
             bool allow_incremental_gc_ = true;
             /** true to report statistics **/
             bool stats_flag_ = false;
+            /** remember basic gc statistics for this many GC's; separately for incremental + full GCs **/
+            std::size_t stats_history_z_ = 256;
             /** true to enable debug logging **/
             bool debug_flag_ = false;
         };
@@ -147,17 +149,24 @@ namespace xo {
             const GCRunstate & runstate() const { return runstate_; }
             const GcStatistics & native_gc_statistics() const { return gc_statistics_; }
             GcStatisticsExt get_gc_statistics() const;
+            const GcStatisticsHistory & gc_history() const { return gc_history_; }
 
             /** true iff GC permitted in current state **/
             bool is_gc_enabled() const { return gc_enabled_ == 0; }
             /** true during (and only during) a GC cycle **/
             bool gc_in_progress() const { return runstate_.in_progress(); }
+            /** @return reserved size of Nursery to-space **/
+            std::size_t nursery_to_reserved() const;
             /** @return committed size of Nursery to-space **/
             std::size_t nursery_to_committed() const;
             /** @return nursery bytes used before checkpoint **/
             std::size_t nursery_before_checkpoint() const;
             /** @return nursery bytes used after checkpoint **/
             std::size_t nursery_after_checkpoint() const;
+            /** @return allocated memory range for nursery **/
+            std::pair<const std::byte *, const std::byte *> nursery_span(role role) const;
+            /** @return reserved size of Tenured to-space **/
+            std::size_t tenured_to_reserved() const;
             /** @return committed size of Tenured to-space **/
             std::size_t tenured_to_committed() const;
             /** @return tenured bytes used before checkpoint **/
@@ -167,8 +176,24 @@ namespace xo {
 
             /** @return generation to which object at @p x belongs **/
             generation_result tospace_generation_of(const void * x) const;
+            /** @return generation to which object at @p x belongs,
+             *          location relative to base address for that generation,
+             *          and allocated size of that generation
+             *          @p role chooses between to-space and from-space
+             **/
+            std::tuple<generation_result, std::size_t, std::size_t> location_of(role role, const void * x) const;
+            /** @return generation to which object at @p x belongs,
+             *          location relative to base address for @p x,
+             *          and allocated size of generation
+             **/
+            std::tuple<generation_result,std::size_t,std::size_t> tospace_location_of(const void * x) const;
             /** @return generation that contains @p x, given it's in from-space **/
             generation_result fromspace_generation_of(const void * x) const;
+            /** @return generation to which object at @p x belongs,
+             *          location relative to base address for @p x,
+             *          and allocated size of generation
+             **/
+            std::tuple<generation_result,std::size_t,std::size_t> fromspace_location_of(const void * x) const;
             /** true iff from-space contains @p x **/
             bool fromspace_contains(const void * x) const;
             /** @return free pointer for generation @p gen, i.e. nursery or tenured space **/
@@ -361,6 +386,9 @@ namespace xo {
             /** enabled when 0.  disabled when <0 **/
             int gc_enabled_ = 0;
 
+            /** rotating per-gc statistics history **/
+            GcStatisticsHistory gc_history_;
+
             /** for (optional) viz: invoke when copying individual objects **/
             GcCopyCallbackSet gc_copy_cbset_;
         };
diff --git a/include/xo/alloc/GcStatistics.hpp b/include/xo/alloc/GcStatistics.hpp
index 24cac461..d73f8947 100644
--- a/include/xo/alloc/GcStatistics.hpp
+++ b/include/xo/alloc/GcStatistics.hpp
@@ -6,6 +6,7 @@
 #pragma once
 
 #include "generation.hpp"
+#include "CircularBuffer.hpp"
 #include "xo/reflect/TypeDescr.hpp"
 #include "xo/indentlog/print/pretty.hpp"
 #include <ostream>
@@ -57,6 +58,8 @@ namespace xo {
          **/
         class GcStatistics {
         public:
+            GcStatistics() = default;
+
             /** update statistics after a GC cycle
              *  @param upto.      nursery -> incremental collection; tenured -> full collection
              *  @param alloc_z.   new allocations (since preceding GC)
@@ -108,6 +111,7 @@ namespace xo {
          **/
         class GcStatisticsExt : public GcStatistics {
         public:
+            GcStatisticsExt() = default;
             explicit GcStatisticsExt(const GcStatistics & x) : GcStatistics{x} {}
 
             /** @param os. write stats on this output stream **/
@@ -128,6 +132,63 @@ namespace xo {
             return os;
         }
 
+        /** @class GcStatisticsHistoryItem
+         *  @brief info we want to record over time (won't have cumulative things in it)
+         **/
+        class GcStatisticsHistoryItem {
+        public:
+            GcStatisticsHistoryItem() = default;
+            GcStatisticsHistoryItem(generation upto,
+                                    std::size_t new_alloc_z,
+                                    std::size_t survive_z,
+                                    std::size_t promote_z,
+                                    std::size_t persist_z,
+                                    std::size_t effort_z,
+                                    std::size_t garbage0_z,
+                                    std::size_t garbage1_z,
+                                    std::size_t garbageN_z)
+                : upto_{upto},
+                  new_alloc_z_{new_alloc_z},
+                  survive_z_{survive_z},
+                  promote_z_{promote_z},
+                  persist_z_{persist_z},
+                  effort_z_{effort_z},
+                  garbage0_z_{garbage0_z},
+                  garbage1_z_{garbage1_z},
+                  garbageN_z_{garbageN_z}
+                {}
+
+            /** @param os. write stats on this output stream **/
+            void display(std::ostream & os) const;
+
+            /** type of GC that generated this record **/
+            generation upto_;
+            /** #of bytes new allocation **/
+            std::size_t new_alloc_z_ = 0;
+            /** #of bytes surviving their first collection (i.e. N0->N1) **/
+            std::size_t survive_z_ = 0;
+            /** #of bytes promoted to tenured.
+             *  Comprises all objects surviving their 2nd collection (i.e. N1->T)
+             **/
+            std::size_t promote_z_ = 0;
+            /** #of bytes surviving 3rd of later collection **/
+            std::size_t persist_z_ = 0;
+            /** #of bytes copied **/
+            std::size_t effort_z_ = 0;
+            /** #of bytes garbage from N0 (i.e. survived 0 GCs) **/
+            std::size_t garbage0_z_ = 0;
+            /** #of bytes garbage from N1 (i.e. survived 1 GCs) **/
+            std::size_t garbage1_z_ = 0;
+            /** #of bytes garbage from T (i.e. survived 2+ GCs) **/
+            std::size_t garbageN_z_ = 0;
+        };
+
+        inline std::ostream & operator<< (std::ostream & os, const GcStatisticsHistoryItem & x) {
+            x.display(os);
+            return os;
+        }
+
+        using GcStatisticsHistory = CircularBuffer<GcStatisticsHistoryItem>;
     } /*namespace gc*/
 
     namespace print {
@@ -145,6 +206,11 @@ namespace xo {
         struct ppdetail<xo::gc::GcStatisticsExt> {
             static bool print_pretty(const ppindentinfo &, const xo::gc::GcStatisticsExt &);
         };
+
+        template<>
+        struct ppdetail<xo::gc::GcStatisticsHistoryItem> {
+            static bool print_pretty(const ppindentinfo &, const xo::gc::GcStatisticsHistoryItem &);
+        };
     } /*namespace print*/
 } /*namespace xo*/
 
diff --git a/include/xo/alloc/ListAlloc.hpp b/include/xo/alloc/ListAlloc.hpp
index 7b592b4e..75b148ac 100644
--- a/include/xo/alloc/ListAlloc.hpp
+++ b/include/xo/alloc/ListAlloc.hpp
@@ -34,6 +34,9 @@ namespace xo {
 
             static up<ListAlloc> make(const std::string & name, std::size_t cz, std::size_t nz, bool debug_flag);
 
+            /** page size used by underlying ArenaAlloc **/
+            std::size_t page_size() const;
+
             /** reset to have at least @p z bytes of storage **/
             bool reset(std::size_t z);
 
diff --git a/include/xo/alloc/generation.hpp b/include/xo/alloc/generation.hpp
index 82c48808..2ed89276 100644
--- a/include/xo/alloc/generation.hpp
+++ b/include/xo/alloc/generation.hpp
@@ -30,6 +30,7 @@ namespace xo {
             tenured,
             not_found
         };
+
     } /*namespace gc*/
 } /*namespace xo*/
 
diff --git a/src/alloc/ArenaAlloc.cpp b/src/alloc/ArenaAlloc.cpp
index 49a2d16d..f3145bb2 100644
--- a/src/alloc/ArenaAlloc.cpp
+++ b/src/alloc/ArenaAlloc.cpp
@@ -113,6 +113,7 @@ namespace xo {
             }
 
             this->committed_z_ = align_offset_z;
+            this->limit_ = this->lo_ + committed_z_;
 
             return true;
         }
@@ -133,6 +134,16 @@ namespace xo {
             }
         }
 
+        std::pair<bool, std::size_t>
+        ArenaAlloc::location_of(const void * x) const
+        {
+            if ((lo_ <= x) && (x < hi_)) {
+                return std::make_pair(true, reinterpret_cast<const std::byte *>(x) - lo_);
+            } else {
+                return std::make_pair(false, 0);
+            }
+        }
+
         void
         ArenaAlloc::capture_object_statistics(capture_phase phase,
                                               ObjectStatistics * p_dest) const
@@ -276,6 +287,7 @@ namespace xo {
                        xtag("z0", z0),
                        xtag("+pad", dz),
                        xtag("z1", z1),
+                       xtag("size", this->size()),
                        xtag("avail", this->available()));
 
             this->free_ptr_ += z1;
diff --git a/src/alloc/GC.cpp b/src/alloc/GC.cpp
index 6ccc4d15..a552ae1e 100644
--- a/src/alloc/GC.cpp
+++ b/src/alloc/GC.cpp
@@ -79,6 +79,8 @@ namespace xo {
             mutation_log_[role2int(role::to_space)] = std::make_unique<MutationLog>();
             defer_mutation_log_ = std::make_unique<MutationLog>();
 
+            this->gc_history_ = CircularBuffer<GcStatisticsHistoryItem>(config.stats_history_z_);
+
             this->checkpoint();
         }
 
@@ -191,6 +193,12 @@ namespace xo {
             return retval;
         }
 
+        std::size_t
+        GC::nursery_to_reserved() const
+        {
+            return nursery_to()->reserved();
+        }
+
         std::size_t
         GC::nursery_to_committed() const
         {
@@ -209,6 +217,17 @@ namespace xo {
             return nursery_to()->after_checkpoint();
         }
 
+        std::pair<const std::byte *, const std::byte *>
+        GC::nursery_span(role role) const {
+            return nursery(role)->allocated_span();
+        }
+
+        std::size_t
+        GC::tenured_to_reserved() const
+        {
+            return tenured_to()->reserved();
+        }
+
         std::size_t
         GC::tenured_to_committed() const
         {
@@ -239,6 +258,40 @@ namespace xo {
             return generation_result::not_found;
         }
 
+        std::tuple<generation_result, std::size_t, std::size_t>
+        GC::location_of(role role, const void *x) const
+        {
+            {
+                auto space = this->tenured(role);
+                auto [is_tenured, offset] = space->location_of(x);
+
+                if (is_tenured)
+                    return std::make_tuple(generation_result::tenured, offset, space->allocated());
+            }
+
+            {
+                auto space = this->nursery(role);
+                auto [is_nursery, offset] = nursery(role)->location_of(x);
+
+                if (is_nursery)
+                    return std::make_tuple(generation_result::nursery, offset, space->allocated());
+            }
+
+            return std::make_tuple(generation_result::not_found, 0, 0);
+        }
+
+        std::tuple<generation_result, std::size_t, std::size_t>
+        GC::tospace_location_of(const void * x) const
+        {
+            return location_of(role::to_space, x);
+        }
+
+        std::tuple<generation_result, std::size_t, std::size_t>
+        GC::fromspace_location_of(const void * x) const
+        {
+            return location_of(role::from_space, x);
+        }
+
         generation_result
         GC::fromspace_generation_of(const void * x) const
         {
@@ -988,8 +1041,11 @@ namespace xo {
         {
             scope log(XO_DEBUG(config_.debug_flag_));
 
-            std::size_t N_allocated = nursery_from()->after_checkpoint();
-            std::size_t T_allocated = tenured_from()->after_checkpoint();
+            std::size_t N0_before_gc = nursery_from()->after_checkpoint();
+            std::size_t N1_before_gc = nursery_from()->before_checkpoint();
+
+            std::size_t T0_before_gc = tenured_from()->after_checkpoint();
+            std::size_t T1_before_gc = tenured_from()->before_checkpoint();
 
             std::size_t N_before_gc = nursery_from()->allocated();
             std::size_t T_before_gc = tenured_from()->allocated();
@@ -998,9 +1054,37 @@ namespace xo {
             std::size_t T_after_gc = tenured_to()->allocated();
             //std::byte * N_free_ptr = nursery_[role2int(role::to_space)]->free_ptr();
 
+            std::size_t new_alloc_z = N0_before_gc;
+            /* survive_z: bytes surviving first collection */
+            std::size_t survive_z = N_after_gc;
+            /* promote_z: bytes surviving 2nd collection */
             std::size_t promote_z = (gc_statistics_.total_promoted_
                                      - gc_statistics_.total_promoted_sab_);
 
+            /* #of bytes copied by this collection cycle */
+            std::size_t effort_z = 0;
+            if (upto == generation::nursery) {
+                effort_z = N_after_gc + promote_z;
+            } else {
+                effort_z += N_after_gc + T_after_gc;
+            }
+
+            /* persist_z: bytes surviving 3rd or later collection */
+            std::size_t persist_z = 0;
+            if (upto == generation::tenured)
+                persist_z = T_after_gc - promote_z;
+            /* #of bytes found to be garbage on first collection
+             * (reminder: N_after_gc consists *entirely* of survives from N0_before_gc;
+             *            + all such survivors are in N_after_gc)
+             */
+            std::size_t garbage0_z = (N0_before_gc - N_after_gc);
+            /* #of bytes found to be garbage on 2nd collection */
+            std::size_t garbage1_z = (N1_before_gc - promote_z);
+            /* #of bytes found to be garbage on 3rd or later collection */
+            std::size_t garbageN_z = 0;
+            if (upto == generation::tenured)
+                garbageN_z = (T_before_gc - T_after_gc + promote_z);
+
             /* Don't reset from-space here, it's unnecessary.
              * Would be permissible, but interferes with GC object modelling in
              * xo-object/utest/GC.test.cpp
@@ -1014,25 +1098,38 @@ namespace xo {
                 this->tenured_to()->checkpoint();
 
             if (log) {
-                log(xtag("N_allocated", N_allocated));
-                log(xtag("N_before_gc", N_before_gc));
+                log(xtag("N0_before_gc", N0_before_gc));
+                log(xtag("N1_before_gc", N1_before_gc));
                 log(xtag("N_after_gc", N_after_gc));
-                log(xtag("T_allocated", T_allocated));
-                log(xtag("T_before_gc", T_before_gc));
+
+                log(xtag("T0_before_gc", T0_before_gc));
+                log(xtag("T1_before_gc", T1_before_gc));
                 log(xtag("T_after_gc", T_after_gc));
             }
 
+            GcStatisticsHistoryItem item(upto,
+                                         new_alloc_z,
+                                         survive_z,
+                                         promote_z,
+                                         persist_z,
+                                         effort_z,
+                                         garbage0_z,
+                                         garbage1_z,
+                                         garbageN_z);
+
+            this->gc_history_.push_back(item);
+
             this->incr_gc_pending_ = false;
-            this->gc_statistics_.include_gc(generation::nursery, N_allocated, N_before_gc, N_after_gc, promote_z);
+            this->gc_statistics_.include_gc(generation::nursery, N0_before_gc, N_before_gc, N_after_gc, promote_z);
 
             if (upto == generation::tenured) {
                 this->full_gc_pending_ = false;
-                this->gc_statistics_.include_gc(generation::tenured, T_allocated, T_before_gc, T_after_gc, 0);
+                this->gc_statistics_.include_gc(generation::tenured, T0_before_gc, T_before_gc, T_after_gc, 0);
             } else {
                 // still want to update tenured stats for current alloc size
                 this->gc_statistics_.update_snapshot(generation::tenured, T_after_gc);
             }
-        }
+        } /*cleanup_phase*/
 
         void
         GC::execute_gc(generation upto)
@@ -1090,6 +1187,9 @@ namespace xo {
 
             this->runstate_ = GCRunstate();
 
+            // not this way.. reports cumulative stats
+            //   this->gc_history_.push_back(this->get_gc_statistics());
+
             log && log("statistics:");
             log && log(gc_statistics_);
         }
diff --git a/src/alloc/GcStatistics.cpp b/src/alloc/GcStatistics.cpp
index 7b7a6ff9..cb7ebebf 100644
--- a/src/alloc/GcStatistics.cpp
+++ b/src/alloc/GcStatistics.cpp
@@ -92,6 +92,22 @@ namespace xo {
                 // << xtag("per_type_stats", per_type_stats_)
                << ">";
         }
+
+        void
+        GcStatisticsHistoryItem::display(std::ostream & os) const
+        {
+            os << "<GcStatisticsHistoryItem"
+               << xrtag("upto", upto_)
+               << xrtag("survive_z", survive_z_)
+               << xrtag("promote_z", promote_z_)
+               << xrtag("persist_z", persist_z_)
+               << xrtag("effort_z", effort_z_)
+               << xrtag("garbage0_z", garbage0_z_)
+               << xrtag("garbage1_z", garbage1_z_)
+               << xrtag("garbageN_z", garbageN_z_)
+               << ">";
+        }
+
     } /*namespace gc*/
 
     namespace print {
@@ -148,7 +164,21 @@ namespace xo {
                                              refrtag("tenured_z", x.tenured_z_));
         }
 
-
+        bool
+        ppdetail<xo::gc::GcStatisticsHistoryItem>::print_pretty(const ppindentinfo & ppii,
+                                                                const xo::gc::GcStatisticsHistoryItem & x)
+        {
+            return ppii.pps()->pretty_struct(ppii,
+                                             "GcStatisticsHistoryItem",
+                                             refrtag("upto", gen2str(x.upto_)),
+                                             refrtag("survive_z", x.survive_z_),
+                                             refrtag("promote_z", x.promote_z_),
+                                             refrtag("persist_z", x.persist_z_),
+                                             refrtag("effort_z", x.effort_z_),
+                                             refrtag("garbage0_z", x.garbage0_z_),
+                                             refrtag("garbage1_z", x.garbage1_z_),
+                                             refrtag("garbageN_z", x.garbageN_z_));
+        }
     } /*namespace print*/
 } /*namespace xo*/
 
diff --git a/src/alloc/ListAlloc.cpp b/src/alloc/ListAlloc.cpp
index 29cdb477..8b0a2dbb 100644
--- a/src/alloc/ListAlloc.cpp
+++ b/src/alloc/ListAlloc.cpp
@@ -70,6 +70,11 @@ namespace xo {
             return s_default_name;
         }
 
+        std::size_t
+        ListAlloc::page_size() const {
+            return hd_->page_size();
+        }
+
         std::size_t
         ListAlloc::size() const {
             return total_z_;
@@ -109,8 +114,9 @@ namespace xo {
         ListAlloc::allocated() const {
             std::size_t total = 0;
 
-            if (hd_)
+            if (hd_) {
                 total += hd_->allocated();
+            }
 
             for (const auto & alloc : full_l_)
                 total += alloc->allocated();
@@ -363,10 +369,17 @@ namespace xo {
         ListAlloc::alloc(std::size_t z) {
             scope log(XO_DEBUG(debug_flag_));
 
+            /* ArenaAlloc::alloc() may modify its own size */
+
+            std::size_t z_pre = hd_->size();
             std::byte * retval = hd_->alloc(z);
 
-            if (retval)
+            if (retval) {
+                std::size_t z_post = hd_->size();
+                this->total_z_ += (z_post - z_pre);
+
                 return retval;
+            }
 
             log && log("space exhausted -> expand");
 
diff --git a/utest/CMakeLists.txt b/utest/CMakeLists.txt
index 907bafcb..379ed925 100644
--- a/utest/CMakeLists.txt
+++ b/utest/CMakeLists.txt
@@ -12,6 +12,7 @@ set(UTEST_SRCS
     GcStatistics.test.cpp
     ObjectStatistics.test.cpp
     Forwarding1.test.cpp
+    CircularBuffer.test.cpp
     generation.test.cpp
 )
 
diff --git a/utest/GcStatistics.test.cpp b/utest/GcStatistics.test.cpp
index 5f2fbe96..f5700f25 100644
--- a/utest/GcStatistics.test.cpp
+++ b/utest/GcStatistics.test.cpp
@@ -76,7 +76,7 @@ namespace xo {
 
             tag_config::tag_color_enabled = false;
 
-            GcStatisticsExt stats({});
+            GcStatisticsExt stats;
 
             std::string s = tostr(stats);
 
@@ -154,7 +154,7 @@ namespace xo {
 
             std::stringstream ss;
             ppconfig ppc;
-            GcStatisticsExt stats({});
+            GcStatisticsExt stats;
 
             std::string actual = toppstr2(ppc, stats);
             std::string expected
diff --git a/utest/ListAlloc.test.cpp b/utest/ListAlloc.test.cpp
index 2db22bf2..0a62fd0b 100644
--- a/utest/ListAlloc.test.cpp
+++ b/utest/ListAlloc.test.cpp
@@ -12,7 +12,10 @@ namespace xo {
     namespace ut {
         TEST_CASE("ListAlloc", "[alloc][gc]")
         {
-            /** teeny weeny allocator **/
+            /** teeny weeny allocator.
+             *  but underlying ArenaAlloc works in multiples of VM page size
+             *  (most likely 4k)
+             **/
             up<ListAlloc> alloc = ListAlloc::make("test", 16, 32, false);
 
             REQUIRE(alloc->name() == "test");
@@ -24,7 +27,7 @@ namespace xo {
             std::byte * mem1 = alloc->alloc(20);
 
             REQUIRE(mem1);
-            REQUIRE(alloc->size() == 16 + 32);
+            REQUIRE(alloc->size() == alloc->page_size());
             /* round up to multiple of 8 */
             REQUIRE(alloc->before_checkpoint() == 24);
             REQUIRE(alloc->after_checkpoint() == 0);
@@ -34,7 +37,7 @@ namespace xo {
             std::byte * mem2 = alloc->alloc(30);
 
             REQUIRE(mem2);
-            REQUIRE(alloc->size() == 16 + 32 + 48);
+            REQUIRE(alloc->size() == alloc->page_size());
             REQUIRE(alloc->before_checkpoint() == 24);
             /* round up to multiple of 8 */
             REQUIRE(alloc->after_checkpoint() == 32);
@@ -42,7 +45,7 @@ namespace xo {
             std::byte * mem3 = alloc->alloc(40);
 
             REQUIRE(mem3);
-            REQUIRE(alloc->size() == 16 + 32 + 48 + 80);
+            REQUIRE(alloc->size() == alloc->page_size());
             REQUIRE(alloc->before_checkpoint() == 24);
             /* already multiple of 8 */
             REQUIRE(alloc->after_checkpoint() == 32 + 40);