[compiler-rt] [scudo] Add unmap and eviction stats to Secondary (PR #210465)

[Sadaf Ebrahimi via llvm-commits]

https://github.com/sadafebrahimi updated https://github.com/llvm/llvm-project/pull/210465

>From fd58c8c35058f207f65ddc0b58e32f4283ab38b3 Mon Sep 17 00:00:00 2001
From: Sadaf Ebrahimi <sadafebrahimi at google.com>
Date: Fri, 17 Jul 2026 23:48:14 +0000
Subject: [PATCH] [scudo] Add unmap and eviction stats to Secondary

Track and print stats on the number of memory unmaps and cache evictions
in the MapAllocator. These statistics track total unmaps, as well as
unmaps triggered by exceeding the maximum cache entry size or the
maximum number of entries in the cache.
---
 compiler-rt/lib/scudo/standalone/secondary.h  | 31 ++++++++++++++++++-
 .../scudo/standalone/tests/secondary_test.cpp |  7 +++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/compiler-rt/lib/scudo/standalone/secondary.h b/compiler-rt/lib/scudo/standalone/secondary.h
index b4a5685080b03..c700e22c0fed0 100644
--- a/compiler-rt/lib/scudo/standalone/secondary.h
+++ b/compiler-rt/lib/scudo/standalone/secondary.h
@@ -72,7 +72,25 @@ template <typename Config> Header *getHeader(const void *Ptr) {
 
 } // namespace LargeBlock
 
-static inline void unmap(MemMapT &MemMap) { MemMap.unmap(); }
+inline atomic_u64 *getUnmapCount() {
+  static atomic_u64 Count = {};
+  return &Count;
+}
+
+inline atomic_u64 *getEvictedCount() {
+  static atomic_u64 Count = {};
+  return &Count;
+}
+
+inline atomic_u64 *getEvictedBySizeCount() {
+  static atomic_u64 Count = {};
+  return &Count;
+}
+
+static inline void unmap(MemMapT &MemMap) {
+  atomic_fetch_add(getUnmapCount(), 1ULL, memory_order_relaxed);
+  MemMap.unmap();
+}
 
 namespace {
 
@@ -234,6 +252,15 @@ class MapAllocatorCache {
     Str->append("Stats: CacheRetrievalStats: SuccessRate: %u/%u "
                 "(%zu.%02zu%%)\n",
                 SuccessfulRetrieves, CallsToRetrieve, Integral, Fractional);
+    Str->append(
+        "Total Unmaps: %llu\n",
+        static_cast<unsigned long long>(atomic_load_relaxed(getUnmapCount())));
+    Str->append("Unmapped (exceeded MaxEntrySize): %llu\n",
+                static_cast<unsigned long long>(
+                    atomic_load_relaxed(getEvictedBySizeCount())));
+    Str->append("Unmapped (exceeded DefaultMaxEntriesCount): %llu\n",
+                static_cast<unsigned long long>(
+                    atomic_load_relaxed(getEvictedCount())));
     Str->append("Cache Entry Info (Most Recent -> Least Recent):\n");
 
     for (CachedBlock &Entry : LRUEntries) {
@@ -366,6 +393,7 @@ class MapAllocatorCache {
       while (LRUEntries.size() >= atomic_load_relaxed(&MaxEntriesCount)) {
         // Save MemMaps of evicted entries to perform unmap outside of lock
         CachedBlock *Entry = LRUEntries.back();
+        atomic_fetch_add(getEvictedCount(), 1ULL, memory_order_relaxed);
         EvictionMemMaps.push_back(Entry->MemMap);
         remove(Entry);
       }
@@ -957,6 +985,7 @@ void MapAllocator<Config>::deallocate(const Options &Options, void *Ptr)
     // Note that the `H->MemMap` is stored on the pages managed by itself. Take
     // over the ownership before unmap() so that any operation along with
     // unmap() won't touch inaccessible pages.
+    atomic_fetch_add(getEvictedBySizeCount(), 1ULL, memory_order_relaxed);
     MemMapT MemMap = H->MemMap;
     unmap(MemMap);
   }
diff --git a/compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp b/compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp
index e6ceb2d8b9317..207ecd0ca2d57 100644
--- a/compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp
@@ -478,6 +478,13 @@ TEST(ScudoSecondaryTest, AllocatorCacheMemoryLeakTest) {
   // Evicted entry should be marked due to unmap callback
   EXPECT_EQ(*reinterpret_cast<scudo::u32 *>(Info.MemMaps[0].getBase()),
             UnmappedMarker);
+  scudo::ScopedString Str;
+  Info.Cache->getStats(&Str);
+  Str.output();
+  EXPECT_NE(strstr(Str.data(), "Total Unmaps: 0"), nullptr);
+  EXPECT_NE(strstr(Str.data(), "Unmapped (exceeded MaxEntrySize): 0"), nullptr);
+  EXPECT_NE(strstr(Str.data(), "Unmapped (exceeded DefaultMaxEntriesCount): 1"),
+            nullptr);
 }
 
 TEST(ScudoSecondaryTest, AllocatorCacheOptions) {