cppgc: Fix DCHECK in statistics collection

Resident set size may be smaller than the recorded size in
StatsCollector due to discarded memory.

Change-Id: I7e052fc4412afc64dc1ed5be6ed7dc9271e6f9d2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3855204
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82709}

include/cppgc/heap-statistics.h

@@ -98,7 +98,7 @@ struct HeapStatistics final {
 
   /** Overall committed amount of memory for the heap. */
   size_t committed_size_bytes = 0;
-  /** Resident amount of memory help by the heap. */
+  /** Resident amount of memory held by the heap. */
   size_t resident_size_bytes = 0;
   /** Amount of memory actually used on the heap. */
   size_t used_size_bytes = 0;

src/heap/cppgc/heap-statistics-collector.cc

@@ -109,7 +109,9 @@ HeapStatistics HeapStatisticsCollector::CollectDetailedStatistics(
     }
   }
 
-  DCHECK_EQ(heap->stats_collector()->allocated_memory_size(),
+  // Resident set size may be smaller than the than the recorded size in
+  // `StatsCollector` due to discarded memory that is tracked on page level.
+  DCHECK_GE(heap->stats_collector()->allocated_memory_size(),
             stats.resident_size_bytes);
   return stats;
 }