From 400ac4f08dfc0e430e6fc4a9ecc215d2b8faaa2b Mon Sep 17 00:00:00 2001
From: Mark Plesko <markples@microsoft.com>
Date: Thu, 22 Feb 2024 01:59:47 -0800
Subject: [PATCH 1/2] Reset inc_failure_count whenever below target, not just
 if decreasing the hc

---
 src/coreclr/gc/gc.cpp | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/coreclr/gc/gc.cpp b/src/coreclr/gc/gc.cpp
index 4d281b16251a1e..b4ee811cc6d368 100644
--- a/src/coreclr/gc/gc.cpp
+++ b/src/coreclr/gc/gc.cpp
@@ -25650,6 +25650,12 @@ int gc_heap::calculate_new_heap_count ()
                 dynamic_heap_count_data.below_target_accumulation = 0;
             }
 
+            if (dynamic_heap_count_data.inc_failure_count)
+            {
+                dprintf (6666, ("[CHP1] shrink, reset inc failure count (was %d)", dynamic_heap_count_data.inc_failure_count));
+                dynamic_heap_count_data.inc_failure_count = 0;
+            }
+
             if (new_n_heaps < n_heaps)
             {
                 dynamic_heap_count_data.last_changed_gc_index = current_gc_index;
@@ -25657,12 +25663,6 @@ int gc_heap::calculate_new_heap_count ()
                 dynamic_heap_count_data.last_changed_stcp = smoothed_median_throughput_cost_percent;
                 dprintf (6666, ("[CHP1] setting last changed gc index to %Id, count to %.3f, stcp to %.3f",
                     dynamic_heap_count_data.last_changed_gc_index, dynamic_heap_count_data.last_changed_count, dynamic_heap_count_data.last_changed_stcp));
-
-                if (dynamic_heap_count_data.inc_failure_count)
-                {
-                    dprintf (6666, ("[CHP1] shrink, reset inc failure count (was %d)", dynamic_heap_count_data.inc_failure_count));
-                    dynamic_heap_count_data.inc_failure_count = 0;
-                }
             }
         }
     }

From 7961d6312449af387129d454aea403d5a4709cfa Mon Sep 17 00:00:00 2001
From: Mark Plesko <markples@microsoft.com>
Date: Thu, 22 Feb 2024 02:35:36 -0800
Subject: [PATCH 2/2] Limit inc_failure_count to 2 and ignore it after 40 GCs

---
 src/coreclr/gc/gc.cpp   | 12 ++++++++----
 src/coreclr/gc/gcpriv.h |  5 ++++-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/coreclr/gc/gc.cpp b/src/coreclr/gc/gc.cpp
index b4ee811cc6d368..92d803351d3a6b 100644
--- a/src/coreclr/gc/gc.cpp
+++ b/src/coreclr/gc/gc.cpp
@@ -25492,10 +25492,14 @@ int gc_heap::calculate_new_heap_count ()
                         {
                             if (((int)dynamic_heap_count_data.last_changed_count > 0) && (dynamic_heap_count_data.last_changed_gc_index > 0.0))
                             {
-                                (dynamic_heap_count_data.inc_failure_count)++;
-                                dprintf (6666, ("[CHP0-4] just grew %d GCs ago, grow more aggressively from %d -> %d more heaps",
-                                    (current_gc_index - dynamic_heap_count_data.last_changed_gc_index), step_up_int, (step_up_int * (dynamic_heap_count_data.inc_failure_count + 1))));
-                                step_up_int *= dynamic_heap_count_data.inc_failure_count + 1;
+                                size_t gc_count_since_last_growth = (current_gc_index - dynamic_heap_count_data.last_changed_gc_index);
+                                if (gc_count_since_last_growth <= dynamic_heap_count_data.inc_failure_gcs_threshold)
+                                {
+                                    dynamic_heap_count_data.inc_failure_count = min(dynamic_heap_count_data.inc_failure_count + 1, dynamic_heap_count_data.inc_failure_limit);
+                                    dprintf (6666, ("[CHP0-4] just grew %d GCs ago, grow more aggressively from %d -> %d more heaps",
+                                        gc_count_since_last_growth, step_up_int, (step_up_int * (dynamic_heap_count_data.inc_failure_count + 1))));
+                                    step_up_int *= dynamic_heap_count_data.inc_failure_count + 1;
+                                }
                             }
                         }
                     }
diff --git a/src/coreclr/gc/gcpriv.h b/src/coreclr/gc/gcpriv.h
index 788cbff9f5e507..bcba2d0ca9df5d 100644
--- a/src/coreclr/gc/gcpriv.h
+++ b/src/coreclr/gc/gcpriv.h
@@ -4339,8 +4339,11 @@ class gc_heap
         // For tuning above/below target tcp.
         //
         // If we just increased the heap count and immediately need to grow again, that counts as a failure.
-        // The higher the failure count, the more aggressive we should grow.
+        // The higher the failure count, the more aggressive we should grow, but only to a point.
         int             inc_failure_count;
+        const int       inc_failure_limit = 2;
+        // After enough GCs without growth, we should stop being aggressive due to the failure count.
+        const int       inc_failure_gcs_threshold = 40;
 
         // If we are trending up and the tcp is already close enough to target, we need this many samples
         // before we adjust.