Bug 1829127 - Add telemetry for PHC utilisation r=glandium

Differential Revision: https://phabricator.services.mozilla.com/D192303

memory/build/PHC.cpp

@@ -841,23 +841,20 @@ class GMut {
   void IncPageAllocMisses(GMutLock) {}
 #endif
 
-#if PHC_LOGGING
-  struct PageStats {
-    size_t mNumAlloced = 0;
-    size_t mNumFreed = 0;
-  };
-
-  PageStats GetPageStats(GMutLock) {
-    PageStats stats;
+  phc::PHCStats GetPageStats(GMutLock) {
+    phc::PHCStats stats;
 
     for (const auto& page : mAllocPages) {
-      stats.mNumAlloced += page.mState == AllocPageState::InUse ? 1 : 0;
-      stats.mNumFreed += page.mState == AllocPageState::Freed ? 1 : 0;
+      stats.mSlotsAllocated += page.mState == AllocPageState::InUse ? 1 : 0;
+      stats.mSlotsFreed += page.mState == AllocPageState::Freed ? 1 : 0;
     }
+    stats.mSlotsUnused =
+        kNumAllocPages - stats.mSlotsAllocated - stats.mSlotsFreed;
 
     return stats;
   }
 
+#if PHC_LOGGING
   size_t PageAllocHits(GMutLock) { return mPageAllocHits; }
   size_t PageAllocAttempts(GMutLock) {
     return mPageAllocHits + mPageAllocMisses;
@@ -1244,12 +1241,12 @@ static void* MaybePageAlloc(const Maybe<arena_id_t>& aArenaId, size_t aReqSize,
 
     gMut->IncPageAllocHits(lock);
 #if PHC_LOGGING
-    GMut::PageStats stats = gMut->GetPageStats(lock);
+    phc::PHCStats stats = gMut->GetPageStats(lock);
 #endif
     LOG("PageAlloc(%zu, %zu) -> %p[%zu]/%p (%zu) (z%zu), sAllocDelay <- %zu, "
         "fullness %zu/%zu/%zu, hits %zu/%zu (%zu%%), lifetime %zu\n",
         aReqSize, aAlignment, pagePtr, i, ptr, usableSize, size_t(aZero),
-        size_t(newAllocDelay), stats.mNumAlloced, stats.mNumFreed,
+        size_t(newAllocDelay), stats.mSlotsAllocated, stats.mSlotsFreed,
         kNumAllocPages, gMut->PageAllocHits(lock),
         gMut->PageAllocAttempts(lock), gMut->PageAllocHitRate(lock), lifetime);
     break;
@@ -1259,12 +1256,12 @@ static void* MaybePageAlloc(const Maybe<arena_id_t>& aArenaId, size_t aReqSize,
     // No pages are available, or VirtualAlloc/mprotect failed.
     gMut->IncPageAllocMisses(lock);
 #if PHC_LOGGING
-    GMut::PageStats stats = gMut->GetPageStats(lock);
+    phc::PHCStats stats = gMut->GetPageStats(lock);
 #endif
     LOG("No PageAlloc(%zu, %zu), sAllocDelay <- %zu, fullness %zu/%zu/%zu, "
         "hits %zu/%zu (%zu%%)\n",
-        aReqSize, aAlignment, size_t(newAllocDelay), stats.mNumAlloced,
-        stats.mNumFreed, kNumAllocPages, gMut->PageAllocHits(lock),
+        aReqSize, aAlignment, size_t(newAllocDelay), stats.mSlotsAllocated,
+        stats.mSlotsFreed, kNumAllocPages, gMut->PageAllocHits(lock),
         gMut->PageAllocAttempts(lock), gMut->PageAllocHitRate(lock));
   }
 
@@ -1509,11 +1506,11 @@ MOZ_ALWAYS_INLINE static bool MaybePageFree(const Maybe<arena_id_t>& aArenaId,
   FreePage(lock, index, aArenaId, freeStack, reuseDelay);
 
 #if PHC_LOGGING
-  GMut::PageStats stats = gMut->GetPageStats(lock);
+  phc::PHCStats stats = gMut->GetPageStats(lock);
 #endif
   LOG("PageFree(%p[%zu]), %zu delay, reuse at ~%zu, fullness %zu/%zu/%zu\n",
       aPtr, index, size_t(reuseDelay), size_t(GAtomic::Now()) + reuseDelay,
-      stats.mNumAlloced, stats.mNumFreed, kNumAllocPages);
+      stats.mSlotsAllocated, stats.mSlotsFreed, kNumAllocPages);
 
   return true;
 }
@@ -1772,6 +1769,14 @@ void PHCMemoryUsage(MemoryUsage& aMemoryUsage) {
   }
 }
 
+void GetPHCStats(PHCStats& aStats) {
+  if (gMut) {
+    MutexAutoLock lock(GMut::sMutex);
+
+    aStats = gMut->GetPageStats(lock);
+  }
+}
+
 // Enable or Disable PHC at runtime.  If PHC is disabled it will still trap
 // bad uses of previous allocations, but won't track any new allocations.
 void SetPHCState(PHCState aState) { gMut->SetState(aState); }

memory/build/PHC.h

@@ -141,6 +141,15 @@ struct MemoryUsage {
 
 MOZ_JEMALLOC_API void PHCMemoryUsage(MemoryUsage& aMemoryUsage);
 
+struct PHCStats {
+  size_t mSlotsAllocated = 0;
+  size_t mSlotsFreed = 0;
+  size_t mSlotsUnused = 0;
+};
+
+// Return PHC memory usage information by filling in the supplied structure.
+MOZ_JEMALLOC_API void GetPHCStats(PHCStats& aStats);
+
 }  // namespace phc
 }  // namespace mozilla
 

toolkit/components/telemetry/Histograms.json

@@ -1751,6 +1751,37 @@
     "description": "Over-allocation due to PHC's rounding (aka internal fragmentation).  Measured in bytes.",
     "releaseChannelCollection": "opt-out"
   },
+  "MEMORY_PHC_SLOTS_ALLOCATED": {
+    "record_in_processes": ["main", "content"],
+    "products": ["firefox"],
+    "alert_emails": [
+      "memshrink-telemetry-alerts@mozilla.com",
+      "pbone@mozilla.com"
+    ],
+    "bug_numbers": [1829127],
+    "expires_in_version": "128",
+    "kind": "exponential",
+    "high": 16384,
+    "n_buckets": 64,
+    "description": "Number of PHC slots currently allocated",
+    "releaseChannelCollection": "opt-out"
+  },
+  "MEMORY_PHC_SLOTS_FREED": {
+    "record_in_processes": ["main", "content"],
+    "products": ["firefox"],
+    "alert_emails": [
+      "memshrink-telemetry-alerts@mozilla.com",
+      "pbone@mozilla.com"
+    ],
+    "bug_numbers": [1829127],
+    "expires_in_version": "128",
+    "kind": "exponential",
+    "high": 16384,
+    "n_buckets": 64,
+    "description": "Number of PHC slots allocated-then-freed",
+    "releaseChannelCollection": "opt-out"
+  },
+
   "FONTLIST_INITOTHERFAMILYNAMES": {
     "record_in_processes": ["main", "content"],
     "products": ["firefox", "fennec"],

xpcom/base/PHCManager.cpp

@@ -38,6 +38,14 @@ void ReportPHCTelemetry() {
   PHCMemoryUsage(usage);
 
   Accumulate(Telemetry::MEMORY_PHC_SLOP, usage.mFragmentationBytes);
+
+  PHCStats stats;
+  GetPHCStats(stats);
+
+  Accumulate(Telemetry::MEMORY_PHC_SLOTS_ALLOCATED, stats.mSlotsAllocated);
+  Accumulate(Telemetry::MEMORY_PHC_SLOTS_FREED, stats.mSlotsFreed);
+  // There are also slots that are unused (neither free nor allocated) they
+  // can be calculated by knowing the total number of slots.
 }
 
 };  // namespace mozilla