[ptr-compr] Extend RegionAllocator functionality + a bit of cleanup.

This CL adds CheckRange() which will be used in DCHECKs in BoundedPageAllocator
and renames "min_region_size" to "page_size" for better readability.

Bug: v8:8096
Change-Id: I62cf7a92e50d0a11d462a9fbc34ddc5eda5456e1
Reviewed-on: https://chromium-review.googlesource.com/1209284Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55692}

src/base/region-allocator.cc

@@ -17,18 +17,17 @@ constexpr double kMaxLoadFactorForRandomization = 0.40;
 constexpr int kMaxRandomizationAttempts = 3;
 
 RegionAllocator::RegionAllocator(Address memory_region_begin,
-                                 size_t memory_region_size,
-                                 size_t min_region_size)
+                                 size_t memory_region_size, size_t page_size)
     : whole_region_(memory_region_begin, memory_region_size, false),
-      region_size_in_min_regions_(size() / min_region_size),
+      region_size_in_pages_(size() / page_size),
       max_load_for_randomization_(
           static_cast<size_t>(size() * kMaxLoadFactorForRandomization)),
       free_size_(0),
-      min_region_size_(min_region_size) {
-  DCHECK_LT(begin(), end());
-  DCHECK(base::bits::IsPowerOfTwo(min_region_size_));
-  CHECK(IsAligned(size(), min_region_size_));
-  CHECK(IsAligned(begin(), min_region_size_));
+      page_size_(page_size) {
+  CHECK_LT(begin(), end());
+  CHECK(base::bits::IsPowerOfTwo(page_size_));
+  CHECK(IsAligned(size(), page_size_));
+  CHECK(IsAligned(begin(), page_size_));
 
   // Initial region.
   Region* region = new Region(whole_region_);
@@ -70,8 +69,10 @@ RegionAllocator::Region* RegionAllocator::FreeListFindRegion(size_t size) {
 }
 
 void RegionAllocator::FreeListRemoveRegion(Region* region) {
+  DCHECK(!region->is_used());
   auto iter = free_regions_.find(region);
   DCHECK_NE(iter, free_regions_.end());
+  DCHECK_EQ(region, *iter);
   DCHECK_LE(region->size(), free_size_);
   free_size_ -= region->size();
   free_regions_.erase(iter);
@@ -79,13 +80,14 @@ void RegionAllocator::FreeListRemoveRegion(Region* region) {
 
 RegionAllocator::Region* RegionAllocator::Split(Region* region,
                                                 size_t new_size) {
-  DCHECK(IsAligned(new_size, min_region_size_));
+  DCHECK(IsAligned(new_size, page_size_));
   DCHECK_GT(region->size(), new_size);
 
   // Create new region and put it to the lists after the |region|.
+  bool used = region->is_used();
   Region* new_region =
-      new Region(region->begin() + new_size, region->size() - new_size, false);
-  if (!region->is_used()) {
+      new Region(region->begin() + new_size, region->size() - new_size, used);
+  if (!used) {
     // Remove region from the free list before updating it's size.
     FreeListRemoveRegion(region);
   }
@@ -93,8 +95,10 @@ RegionAllocator::Region* RegionAllocator::Split(Region* region,
 
   all_regions_.insert(new_region);
 
+  if (!used) {
     FreeListAddRegion(region);
     FreeListAddRegion(new_region);
+  }
   return new_region;
 }
 
@@ -114,7 +118,7 @@ void RegionAllocator::Merge(AllRegionsSet::iterator prev_iter,
 
 RegionAllocator::Address RegionAllocator::AllocateRegion(size_t size) {
   DCHECK_NE(size, 0);
-  DCHECK(IsAligned(size, min_region_size_));
+  DCHECK(IsAligned(size, page_size_));
 
   Region* region = FreeListFindRegion(size);
   if (region == nullptr) return kAllocationFailure;
@@ -122,7 +126,7 @@ RegionAllocator::Address RegionAllocator::AllocateRegion(size_t size) {
   if (region->size() != size) {
     Split(region, size);
   }
-  DCHECK(IsAligned(region->begin(), min_region_size_));
+  DCHECK(IsAligned(region->begin(), page_size_));
   DCHECK_EQ(region->size(), size);
 
   // Mark region as used.
@@ -139,8 +143,7 @@ RegionAllocator::Address RegionAllocator::AllocateRegion(
 
     for (int i = 0; i < kMaxRandomizationAttempts; i++) {
       rng->NextBytes(&random, sizeof(random));
-      size_t random_offset =
-          min_region_size_ * (random % region_size_in_min_regions_);
+      size_t random_offset = page_size_ * (random % region_size_in_pages_);
       Address address = begin() + random_offset;
       if (AllocateRegionAt(address, size)) {
         return address;
@@ -152,9 +155,9 @@ RegionAllocator::Address RegionAllocator::AllocateRegion(
 }
 
 bool RegionAllocator::AllocateRegionAt(Address requested_address, size_t size) {
-  DCHECK(IsAligned(requested_address, min_region_size_));
+  DCHECK(IsAligned(requested_address, page_size_));
   DCHECK_NE(size, 0);
-  DCHECK(IsAligned(size, min_region_size_));
+  DCHECK(IsAligned(size, page_size_));
 
   Address requested_end = requested_address + size;
   DCHECK_LE(requested_end, end());
@@ -174,7 +177,7 @@ bool RegionAllocator::AllocateRegionAt(Address requested_address, size_t size) {
   if (region->begin() != requested_address) {
     // Split the region at the |requested_address| boundary.
     size_t new_size = requested_address - region->begin();
-    DCHECK(IsAligned(new_size, min_region_size_));
+    DCHECK(IsAligned(new_size, page_size_));
     region = Split(region, new_size);
   }
   if (region->end() != requested_end) {
@@ -236,6 +239,18 @@ size_t RegionAllocator::FreeRegion(Address address) {
   return size;
 }
 
+size_t RegionAllocator::CheckRegion(Address address) {
+  AllRegionsSet::iterator region_iter = FindRegion(address);
+  if (region_iter == all_regions_.end()) {
+    return 0;
+  }
+  Region* region = *region_iter;
+  if (region->begin() != address || !region->is_used()) {
+    return 0;
+  }
+  return region->size();
+}
+
 void RegionAllocator::Region::Print(std::ostream& os) const {
   std::ios::fmtflags flags = os.flags(std::ios::hex | std::ios::showbase);
   os << "[" << begin() << ", " << end() << "), size: " << size();
@@ -248,7 +263,7 @@ void RegionAllocator::Print(std::ostream& os) const {
   os << "RegionAllocator: [" << begin() << ", " << end() << ")";
   os << "\nsize: " << size();
   os << "\nfree_size: " << free_size();
-  os << "\nmin_region_size: " << min_region_size_;
+  os << "\npage_size: " << page_size_;
 
   os << "\nall regions: ";
   for (const Region* region : all_regions_) {

src/base/region-allocator.h

@@ -14,8 +14,8 @@ namespace v8 {
 namespace base {
 
 // Helper class for managing used/free regions within [address, address+size)
-// region. Minimum allocation unit is |min_region_size|.
-// Requested allocation size is rounded up to |min_region_size|.
+// region. Minimum allocation unit is |page_size|. Requested allocation size
+// is rounded up to |page_size|.
 // The region allocation algorithm implements best-fit with coalescing strategy:
 // it tries to find a smallest suitable free region upon allocation and tries
 // to merge region with its neighbors upon freeing.
@@ -28,33 +28,46 @@ class V8_BASE_EXPORT RegionAllocator final {
 
   static constexpr Address kAllocationFailure = static_cast<Address>(-1);
 
-  RegionAllocator(Address address, size_t size, size_t min_region_size);
+  RegionAllocator(Address address, size_t size, size_t page_size);
   ~RegionAllocator();
 
-  // Allocates region of |size| (must be |min_region_size|-aligned). Returns
+  // Allocates region of |size| (must be |page_size|-aligned). Returns
   // the address of the region on success or kAllocationFailure.
   Address AllocateRegion(size_t size);
   // Same as above but tries to randomize the region displacement.
   Address AllocateRegion(RandomNumberGenerator* rng, size_t size);
 
   // Allocates region of |size| at |requested_address| if it's free. Both the
-  // address and the size must be |min_region_size|-aligned. On success returns
+  // address and the size must be |page_size|-aligned. On success returns
   // true.
   // This kind of allocation is supposed to be used during setup phase to mark
   // certain regions as used or for randomizing regions displacement.
   bool AllocateRegionAt(Address requested_address, size_t size);
 
   // Frees region at given |address|, returns the size of the region.
-  // The region must be previously allocated. Return 0 on failure.
+  // There must be a used region starting at given address otherwise nothing
+  // will be freed and 0 will be returned.
   size_t FreeRegion(Address address);
 
+  // If there is a used region starting at given address returns its size
+  // otherwise 0.
+  size_t CheckRegion(Address address);
+
   Address begin() const { return whole_region_.begin(); }
   Address end() const { return whole_region_.end(); }
   size_t size() const { return whole_region_.size(); }
 
+  bool contains(Address address) const {
+    return whole_region_.contains(address);
+  }
+
   // Total size of not yet aquired regions.
   size_t free_size() const { return free_size_; }
 
+  // The alignment of the allocated region's addresses and granularity of
+  // the allocated region's sizes.
+  size_t page_size() const { return page_size_; }
+
   void Print(std::ostream& os) const;
 
  private:
@@ -88,8 +101,8 @@ class V8_BASE_EXPORT RegionAllocator final {
   // The whole region.
   const Region whole_region_;
 
-  // Number of |min_region_size_| in the whole region.
-  const size_t region_size_in_min_regions_;
+  // Number of |page_size_| in the whole region.
+  const size_t region_size_in_pages_;
 
   // If the free size is less than this value - stop trying to randomize the
   // allocation addresses.
@@ -99,7 +112,7 @@ class V8_BASE_EXPORT RegionAllocator final {
   size_t free_size_;
 
   // Minimum region size. Must be a pow of 2.
-  const size_t min_region_size_;
+  const size_t page_size_;
 
   struct AddressEndOrder {
     bool operator()(const Region* a, const Region* b) const {