[scudo] Dump MapAllocatorCache::retrieve() data

Keeps track of CallsToRetrieve, how many SuccessfulRetrieves, from
cached block allocations. Dumps this data in the
MapAllocatorCache::getStats() function

Reviewed By: cferris, Chia-hungDuan

Differential Revision: https://reviews.llvm.org/D157154

Author: Fernando

compiler-rt/lib/scudo/standalone/secondary.h

@@ -155,10 +155,22 @@ template <typename Config> class MapAllocatorCache {
 
   void getStats(ScopedString *Str) {
     ScopedLock L(Mutex);
+    u32 Integral = 0;
+    u32 Fractional = 0;
+    if (CallsToRetrieve != 0) {
+      Integral = SuccessfulRetrieves * 100 / CallsToRetrieve;
+      Fractional = (((SuccessfulRetrieves * 100) % CallsToRetrieve) * 100 +
+                    CallsToRetrieve / 2) /
+                   CallsToRetrieve;
+    }
     Str->append("Stats: MapAllocatorCache: EntriesCount: %d, "
                 "MaxEntriesCount: %u, MaxEntrySize: %zu\n",
                 EntriesCount, atomic_load_relaxed(&MaxEntriesCount),
                 atomic_load_relaxed(&MaxEntrySize));
+    Str->append("Stats: CacheRetrievalStats: SuccessRate: %u/%u "
+                "(%u.%02u%%)\n",
+                SuccessfulRetrieves, CallsToRetrieve,
+                Integral, Fractional);
     for (CachedBlock Entry : Entries) {
       if (!Entry.isValid())
         continue;
@@ -272,6 +284,7 @@ template <typename Config> class MapAllocatorCache {
     uptr HeaderPos = 0;
     {
       ScopedLock L(Mutex);
+      CallsToRetrieve++;
       if (EntriesCount == 0)
         return false;
       for (u32 I = 0; I < MaxCount; I++) {
@@ -292,6 +305,7 @@ template <typename Config> class MapAllocatorCache {
         Entry = Entries[I];
         Entries[I].invalidate();
         EntriesCount--;
+        SuccessfulRetrieves++;
         break;
       }
     }
@@ -428,6 +442,8 @@ template <typename Config> class MapAllocatorCache {
   u64 OldestTime GUARDED_BY(Mutex) = 0;
   u32 IsFullEvents GUARDED_BY(Mutex) = 0;
   atomic_s32 ReleaseToOsIntervalMs = {};
+  u32 CallsToRetrieve GUARDED_BY(Mutex) = 0;
+  u32 SuccessfulRetrieves GUARDED_BY(Mutex) = 0;
 
   CachedBlock Entries[CacheConfig::EntriesArraySize] GUARDED_BY(Mutex) = {};
   NonZeroLengthArray<CachedBlock, CacheConfig::QuarantineSize>