RFC: use some in-memory state in SimpleCache to quickly cache-miss some CantConditionalize cases

net/disk_cache/simple/simple_index.cc

Index: net/disk_cache/simple/simple_index.cc
diff --git a/net/disk_cache/simple/simple_index.cc b/net/disk_cache/simple/simple_index.cc
index c41c829bdefd808db4ea55dded03e54f4574b641..e65e251fa739e393a6cb43e342c51f48496839f6 100644
--- a/net/disk_cache/simple/simple_index.cc
+++ b/net/disk_cache/simple/simple_index.cc
@@ -60,7 +60,8 @@ EntryMetadata::EntryMetadata()
 
 EntryMetadata::EntryMetadata(base::Time last_used_time,
                              base::StrictNumeric<uint32_t> entry_size)
-    : last_used_time_seconds_since_epoch_(0), entry_size_(entry_size) {
+    : last_used_time_seconds_since_epoch_(0), entry_size_(0) {
+  SetEntrySize(entry_size);  // to round/pack properly.
   SetLastUsedTime(last_used_time);
 }
 
@@ -88,11 +89,12 @@ void EntryMetadata::SetLastUsedTime(const base::Time& last_used_time) {
 }
 
 uint32_t EntryMetadata::GetEntrySize() const {
-  return entry_size_;
+  return entry_size_ << 8;
 }
 
 void EntryMetadata::SetEntrySize(base::StrictNumeric<uint32_t> entry_size) {
-  entry_size_ = entry_size;
+  // ### what happens if we overflow here?
+  entry_size_ = (static_cast<uint32_t>(entry_size) + 255) >> 8;
 }
 
 void EntryMetadata::Serialize(base::Pickle* pickle) const {
@@ -100,11 +102,13 @@ void EntryMetadata::Serialize(base::Pickle* pickle) const {
   int64_t internal_last_used_time = GetLastUsedTime().ToInternalValue();
   // If you modify the size of the size of the pickle, be sure to update
   // kOnDiskSizeBytes.
+  uint32_t packed_entry_info = (entry_size_ << 8) | memory_entry_data_;
   pickle->WriteInt64(internal_last_used_time);
-  pickle->WriteUInt64(entry_size_);
+  pickle->WriteUInt64(packed_entry_info);
 }
 
-bool EntryMetadata::Deserialize(base::PickleIterator* it) {
+bool EntryMetadata::Deserialize(base::PickleIterator* it,
+                                bool has_memory_entry_data) {
   DCHECK(it);
   int64_t tmp_last_used_time;
   uint64_t tmp_entry_size;
@@ -112,7 +116,14 @@ bool EntryMetadata::Deserialize(base::PickleIterator* it) {
       tmp_entry_size > std::numeric_limits<decltype(entry_size_)>::max())
     return false;
   SetLastUsedTime(base::Time::FromInternalValue(tmp_last_used_time));
-  entry_size_ = static_cast<uint32_t>(tmp_entry_size);
+  if (has_memory_entry_data) {
+    // tmp_entry_size actually packs entry_size_ and memory_entry_data_.
+    SetEntrySize(static_cast<uint32_t>(tmp_entry_size & 0xFFFFFF00));
+    SetMemoryEntryData(static_cast<uint8_t>(tmp_entry_size & 0xFF));
+  } else {
+    SetEntrySize(static_cast<uint32_t>(tmp_entry_size));
+    SetMemoryEntryData(0);
+  }
   return true;
 }
 
@@ -281,6 +292,22 @@ bool SimpleIndex::Has(uint64_t hash) const {
   return !initialized_ || entries_set_.count(hash) > 0;
 }
 
+uint8_t SimpleIndex::GetMemoryEntryData(uint64_t entry_hash) const {
+  DCHECK(io_thread_checker_.CalledOnValidThread());
+  EntrySet::const_iterator it = entries_set_.find(entry_hash);
+  if (it == entries_set_.end())
+    return 0;
+  return it->second.GetMemoryEntryData();
+}
+
+void SimpleIndex::SetMemoryEntryData(uint64_t entry_hash, uint8_t value) {
+  DCHECK(io_thread_checker_.CalledOnValidThread());
+  EntrySet::iterator it = entries_set_.find(entry_hash);
+  if (it == entries_set_.end())
+    return;
+  return it->second.SetMemoryEntryData(value);
+}
+
 bool SimpleIndex::UseIfExists(uint64_t entry_hash) {
   DCHECK(io_thread_checker_.CalledOnValidThread());
   // Always update the last used time, even if it is during initialization.
@@ -410,8 +437,9 @@ void SimpleIndex::UpdateEntryIteratorSize(
   DCHECK(io_thread_checker_.CalledOnValidThread());
   DCHECK_GE(cache_size_, (*it)->second.GetEntrySize());
   cache_size_ -= (*it)->second.GetEntrySize();
-  cache_size_ += static_cast<uint32_t>(entry_size);
   (*it)->second.SetEntrySize(entry_size);
+  // We use GetEntrySize to get consistent rounding.
+  cache_size_ += (*it)->second.GetEntrySize();
 }
 
 void SimpleIndex::MergeInitializingSet(