Increase allocation register capacity for desktop platforms

base/trace_event/heap_profiler_allocation_register.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/trace_event/heap_profiler_allocation_register.h"
 
 #include <algorithm>
 
 #include "base/trace_event/trace_event_memory_overhead.h"
 
@@ skipping 42 matching lines @@
   // per backtrace. They were found by replaying real backtraces from Linux
   // and Android against different hash functions.
   return (total_value * 131101) >> 14;
 }
 
 size_t AllocationRegister::AddressHasher::operator () (
     const void* address) const {
   // The multiplicative hashing scheme from [Knuth 1998]. The value of |a| has
   // been chosen carefully based on measurements with real-word data (addresses
   // recorded from a Chrome trace run). It is the first prime after 2^17. For
-  // |shift|, 13, 14 and 15 yield good results. These values are tuned to 2^18
-  // buckets. Microbenchmarks show that this simple scheme outperforms fancy
-  // hashes like Murmur3 by 20 to 40 percent.
+  // |shift|, 15 yield good results for both 2^18 and 2^19 bucket sizes.
+  // Microbenchmarks show that this simple scheme outperforms fancy hashes like
+  // Murmur3 by 20 to 40 percent.
   const uintptr_t key = reinterpret_cast<uintptr_t>(address);
   const uintptr_t a = 131101;
-  const uintptr_t shift = 14;
+  const uintptr_t shift = 15;
   const uintptr_t h = (key * a) >> shift;
   return h;
 }
 
 AllocationRegister::AllocationRegister()
     : AllocationRegister(kAllocationCapacity, kBacktraceCapacity) {}
 
 AllocationRegister::AllocationRegister(size_t allocation_capacity,
                                        size_t backtrace_capacity)
     : allocations_(allocation_capacity),
@@ skipping 92 matching lines @@
       address_and_info.first,
       address_and_info.second.size,
       AllocationContext(
           backtrace_and_count.first,
           address_and_info.second.type_name)
   };
 }
 
 }  // namespace trace_event
 }  // namespace base