[scudo] Add EnableContiguousRegions mode (#85149)

This releases the requirement that we need to preserve the memory for
all regions at the beginning. It needs a huge amount of contiguous pages
and which may be a challenge in certain cases. Therefore, adding a new
flag, EnableContiguousRegions, to indicate whether we want to allocate
all the regions next to each other.

Note that once the EnableContiguousRegions is disabled,
EnableRandomOffset becomes irrelevant because the base of each region is
already random.

Author: ChiaHungDuan

compiler-rt/lib/scudo/standalone/allocator_config.def

@@ -87,9 +87,14 @@ PRIMARY_REQUIRED(const s32, MaxReleaseToOsIntervalMs)
 // PRIMARY_OPTIONAL(TYPE, NAME, DEFAULT)
 //
 // Indicates support for offsetting the start of a region by a random number of
-// pages. Only used with primary64.
+// pages. This is only used if `EnableContiguousRegions` is enabled.
 PRIMARY_OPTIONAL(const bool, EnableRandomOffset, false)
 
+// When `EnableContiguousRegions` is true, all regions will be be arranged in
+// adjacency. This will reduce the fragmentation caused by region allocations
+// but may require a huge amount of contiguous pages at initialization.
+PRIMARY_OPTIONAL(const bool, EnableContiguousRegions, true)
+
 // PRIMARY_OPTIONAL_TYPE(NAME, DEFAULT)
 //
 // Use condition variable to shorten the waiting time of refillment of

compiler-rt/lib/scudo/standalone/primary64.h

@@ -117,40 +117,30 @@ template <typename Config> class SizeClassAllocator64 {
     SmallerBlockReleasePageDelta =
         PagesInGroup * (1 + MinSizeClass / 16U) / 100;
 
-    // Reserve the space required for the Primary.
-    CHECK(ReservedMemory.create(/*Addr=*/0U, PrimarySize,
-                                "scudo:primary_reserve"));
-    PrimaryBase = ReservedMemory.getBase();
-    DCHECK_NE(PrimaryBase, 0U);
-
     u32 Seed;
     const u64 Time = getMonotonicTimeFast();
     if (!getRandom(reinterpret_cast<void *>(&Seed), sizeof(Seed)))
-      Seed = static_cast<u32>(Time ^ (PrimaryBase >> 12));
+      Seed = static_cast<u32>(Time ^ (reinterpret_cast<uptr>(&Seed) >> 12));
 
-    for (uptr I = 0; I < NumClasses; I++) {
-      RegionInfo *Region = getRegionInfo(I);
+    for (uptr I = 0; I < NumClasses; I++)
+      getRegionInfo(I)->RandState = getRandomU32(&Seed);
 
-      // The actual start of a region is offset by a random number of pages
-      // when PrimaryEnableRandomOffset is set.
-      Region->RegionBeg = (PrimaryBase + (I << RegionSizeLog)) +
-                          (Config::getEnableRandomOffset()
-                               ? ((getRandomModN(&Seed, 16) + 1) * PageSize)
-                               : 0);
-      Region->RandState = getRandomU32(&Seed);
-      // Releasing small blocks is expensive, set a higher threshold to avoid
-      // frequent page releases.
-      if (isSmallBlock(getSizeByClassId(I)))
-        Region->TryReleaseThreshold = PageSize * SmallerBlockReleasePageDelta;
-      else
-        Region->TryReleaseThreshold = PageSize;
-      Region->ReleaseInfo.LastReleaseAtNs = Time;
+    if (Config::getEnableContiguousRegions()) {
+      ReservedMemoryT ReservedMemory = {};
+      // Reserve the space required for the Primary.
+      CHECK(ReservedMemory.create(/*Addr=*/0U, RegionSize * NumClasses,
+                                  "scudo:primary_reserve"));
+      const uptr PrimaryBase = ReservedMemory.getBase();
+
+      for (uptr I = 0; I < NumClasses; I++) {
+        MemMapT RegionMemMap = ReservedMemory.dispatch(
+            PrimaryBase + (I << RegionSizeLog), RegionSize);
+        RegionInfo *Region = getRegionInfo(I);
 
-      Region->MemMapInfo.MemMap = ReservedMemory.dispatch(
-          PrimaryBase + (I << RegionSizeLog), RegionSize);
-      CHECK(Region->MemMapInfo.MemMap.isAllocated());
+        initRegion(Region, I, RegionMemMap, Config::getEnableRandomOffset());
+      }
+      shuffle(RegionInfoArray, NumClasses, &Seed);
     }
-    shuffle(RegionInfoArray, NumClasses, &Seed);
 
     // The binding should be done after region shuffling so that it won't bind
     // the FLLock from the wrong region.
@@ -160,14 +150,17 @@ template <typename Config> class SizeClassAllocator64 {
     setOption(Option::ReleaseInterval, static_cast<sptr>(ReleaseToOsInterval));
   }
 
-  void unmapTestOnly() NO_THREAD_SAFETY_ANALYSIS {
+  void unmapTestOnly() {
     for (uptr I = 0; I < NumClasses; I++) {
       RegionInfo *Region = getRegionInfo(I);
+      {
+        ScopedLock ML(Region->MMLock);
+        MemMapT MemMap = Region->MemMapInfo.MemMap;
+        if (MemMap.isAllocated())
+          MemMap.unmap(MemMap.getBase(), MemMap.getCapacity());
+      }
       *Region = {};
     }
-    if (PrimaryBase)
-      ReservedMemory.release();
-    PrimaryBase = 0U;
   }
 
   // When all blocks are freed, it has to be the same size as `AllocatedUser`.
@@ -251,9 +244,10 @@ template <typename Config> class SizeClassAllocator64 {
         }
 
         const bool RegionIsExhausted = Region->Exhausted;
-        if (!RegionIsExhausted)
+        if (!RegionIsExhausted) {
           PopCount = populateFreeListAndPopBlocks(C, ClassId, Region, ToArray,
                                                   MaxBlockCount);
+        }
         ReportRegionExhausted = !RegionIsExhausted && Region->Exhausted;
         break;
       }
@@ -514,7 +508,6 @@ template <typename Config> class SizeClassAllocator64 {
 private:
   static const uptr RegionSize = 1UL << RegionSizeLog;
   static const uptr NumClasses = SizeClassMap::NumClasses;
-  static const uptr PrimarySize = RegionSize * NumClasses;
 
   static const uptr MapSizeIncrement = Config::getMapSizeIncrement();
   // Fill at most this number of batches from the newly map'd memory.
@@ -570,9 +563,14 @@ template <typename Config> class SizeClassAllocator64 {
   }
 
   uptr getRegionBaseByClassId(uptr ClassId) {
-    return roundDown(getRegionInfo(ClassId)->RegionBeg - PrimaryBase,
-                     RegionSize) +
-           PrimaryBase;
+    RegionInfo *Region = getRegionInfo(ClassId);
+    Region->MMLock.assertHeld();
+
+    if (!Config::getEnableContiguousRegions() &&
+        !Region->MemMapInfo.MemMap.isAllocated()) {
+      return 0U;
+    }
+    return Region->MemMapInfo.MemMap.getBase();
   }
 
   static CompactPtrT compactPtrInternal(uptr Base, uptr Ptr) {
@@ -602,6 +600,30 @@ template <typename Config> class SizeClassAllocator64 {
     return BlockSize > PageSize;
   }
 
+  ALWAYS_INLINE void initRegion(RegionInfo *Region, uptr ClassId,
+                                MemMapT MemMap, bool EnableRandomOffset)
+      REQUIRES(Region->MMLock) {
+    DCHECK(!Region->MemMapInfo.MemMap.isAllocated());
+    DCHECK(MemMap.isAllocated());
+
+    const uptr PageSize = getPageSizeCached();
+
+    Region->MemMapInfo.MemMap = MemMap;
+
+    Region->RegionBeg = MemMap.getBase();
+    if (EnableRandomOffset) {
+      Region->RegionBeg +=
+          (getRandomModN(&Region->RandState, 16) + 1) * PageSize;
+    }
+
+    // Releasing small blocks is expensive, set a higher threshold to avoid
+    // frequent page releases.
+    if (isSmallBlock(getSizeByClassId(ClassId)))
+      Region->TryReleaseThreshold = PageSize * SmallerBlockReleasePageDelta;
+    else
+      Region->TryReleaseThreshold = PageSize;
+  }
+
   void pushBatchClassBlocks(RegionInfo *Region, CompactPtrT *Array, u32 Size)
       REQUIRES(Region->FLLock) {
     DCHECK_EQ(Region, getRegionInfo(SizeClassMap::BatchClassId));
@@ -989,9 +1011,26 @@ template <typename Config> class SizeClassAllocator64 {
                                             CompactPtrT *ToArray,
                                             const u16 MaxBlockCount)
       REQUIRES(Region->MMLock) EXCLUDES(Region->FLLock) {
+    if (!Config::getEnableContiguousRegions() &&
+        !Region->MemMapInfo.MemMap.isAllocated()) {
+      ReservedMemoryT ReservedMemory;
+      if (UNLIKELY(!ReservedMemory.create(/*Addr=*/0U, RegionSize,
+                                          "scudo:primary_reserve",
+                                          MAP_ALLOWNOMEM))) {
+        Printf("Can't reserve pages for size class %zu.\n",
+               getSizeByClassId(ClassId));
+        Region->Exhausted = true;
+        return 0U;
+      }
+      initRegion(Region, ClassId,
+                 ReservedMemory.dispatch(ReservedMemory.getBase(),
+                                         ReservedMemory.getCapacity()),
+                 /*EnableRandomOffset=*/false);
+    }
+
+    DCHECK(Region->MemMapInfo.MemMap.isAllocated());
     const uptr Size = getSizeByClassId(ClassId);
     const u16 MaxCount = CacheT::getMaxCached(Size);
-
     const uptr RegionBeg = Region->RegionBeg;
     const uptr MappedUser = Region->MemMapInfo.MappedUser;
     const uptr TotalUserBytes =
@@ -1683,10 +1722,6 @@ template <typename Config> class SizeClassAllocator64 {
       Region->FLLockCV.notifyAll(Region->FLLock);
   }
 
-  // TODO: `PrimaryBase` can be obtained from ReservedMemory. This needs to be
-  // deprecated.
-  uptr PrimaryBase = 0;
-  ReservedMemoryT ReservedMemory = {};
   // The minimum size of pushed blocks that we will try to release the pages in
   // that size class.
   uptr SmallerBlockReleasePageDelta = 0;

compiler-rt/lib/scudo/standalone/tests/primary_test.cpp

@@ -90,6 +90,7 @@ template <typename SizeClassMapT> struct TestConfig3 {
     static const scudo::s32 MaxReleaseToOsIntervalMs = INT32_MAX;
     typedef scudo::uptr CompactPtrT;
     static const scudo::uptr CompactPtrScale = 0;
+    static const bool EnableContiguousRegions = false;
     static const bool EnableRandomOffset = true;
     static const scudo::uptr MapSizeIncrement = 1UL << 18;
   };