Disk cache: Re-open the deleted list length experiment.

BUG=79186
TEST=none
Review URL: http://codereview.chromium.org/7036028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@85826 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 54 insertions, 26 deletions

diff --git a/net/disk_cache/backend_impl.cc b/net/disk_cache/backend_impl.cc
index fc64f9bd..b60b8c0 100644
--- a/net/disk_cache/backend_impl.cc
+++ b/net/disk_cache/backend_impl.cc
@@ -147,9 +147,25 @@ bool DelayedCacheCleanup(const FilePath& full_path) {
   return true;
 }
 
+// Initializes the field trial structures to allow performance measurements
+// for the current cache configuration.
+void SetFieldTrialInfo(int group) {
+  static bool first = true;
+  if (!first)
+    return;
+
+  // Field trials involve static objects so we have to do this only once.
+  first = false;
+  std::string group1 = base::StringPrintf("CacheListSize_%d", group);
+  int probability = 10;
+  scoped_refptr<base::FieldTrial> trial1(
+      new base::FieldTrial("CacheListSize", probability, group1, 2011, 9, 30));
+  trial1->AppendGroup(group1, probability);
+}
+
 // Sets group for the current experiment. Returns false if the files should be
 // discarded.
-bool InitExperiment(disk_cache::IndexHeader* header) {
+bool InitExperiment(disk_cache::IndexHeader* header, uint32 mask) {
   if (header->experiment == disk_cache::EXPERIMENT_OLD_FILE1 ||
       header->experiment == disk_cache::EXPERIMENT_OLD_FILE2) {
     // Discard current cache.
@@ -157,28 +173,35 @@ bool InitExperiment(disk_cache::IndexHeader* header) {
   }
 
   // See if we already defined the group for this profile.
-  if (header->experiment >= disk_cache::EXPERIMENT_DELETED_LIST_OUT)
+  if (header->experiment > disk_cache::EXPERIMENT_DELETED_LIST_OUT) {
+    SetFieldTrialInfo(header->experiment);
     return true;
+  }
 
-  // The experiment is closed.
-  header->experiment = disk_cache::EXPERIMENT_DELETED_LIST_OUT;
-  return true;
-}
+  if (!header->create_time || !header->lru.filled)
+    return true; // Wait untill we fill up the cache.
 
-// Initializes the field trial structures to allow performance measurements
-// for the current cache configuration.
-void SetFieldTrialInfo(int size_group) {
-  static bool first = true;
-  if (!first)
-    return;
+  int index_load = header->num_entries * 100 / (mask + 1);
+  if (index_load > 25) {
+   // Out of the experiment (~18% users).
+   header->experiment = disk_cache::EXPERIMENT_DELETED_LIST_OUT2;
+   return true;
+  }
 
-  // Field trials involve static objects so we have to do this only once.
-  first = false;
-  std::string group1 = base::StringPrintf("CacheSizeGroup_%d", size_group);
-  int totalProbability = 10;
-  scoped_refptr<base::FieldTrial> trial1(
-      new base::FieldTrial("CacheSize", totalProbability, group1, 2011, 6, 30));
-  trial1->AppendGroup(group1, totalProbability);
+  int option = base::RandInt(0, 4);
+  if (option > 1) {
+   // 60% out (49% of the total).
+   header->experiment = disk_cache::EXPERIMENT_DELETED_LIST_OUT2;
+  } else if (!option) {
+   // About 16% of the total.
+   header->experiment = disk_cache::EXPERIMENT_DELETED_LIST_CONTROL;
+  } else {
+   // About 16% of the total.
+   header->experiment = disk_cache::EXPERIMENT_DELETED_LIST_IN;
+  }
+
+  SetFieldTrialInfo(header->experiment);
+  return true;
 }
 
 // ------------------------------------------------------------------------
@@ -470,7 +493,7 @@ int BackendImpl::SyncInit() {
 
   if (!(user_flags_ & disk_cache::kNoRandom) &&
       cache_type_ == net::DISK_CACHE &&
-      !InitExperiment(&data_->header))
+      !InitExperiment(&data_->header, mask_))
     return net::ERR_FAILED;
 
   // We don't care if the value overflows. The only thing we care about is that
@@ -497,10 +520,6 @@ int BackendImpl::SyncInit() {
     read_only_ = true;
   }
 
-  // Setup load-time data only for the main cache.
-  if (cache_type() == net::DISK_CACHE)
-    SetFieldTrialInfo(GetSizeGroup());
-
   eviction_.Init(this);
 
   // stats_ and rankings_ may end up calling back to us so we better be enabled.
@@ -1059,6 +1078,13 @@ void BackendImpl::FirstEviction() {
   if (!GetEntryCount())
     return;  // This is just for unit tests.
 
+  if (!(user_flags_ & disk_cache::kNoRandom) &&
+      cache_type_ == net::DISK_CACHE) {
+    // We were waiting for the first eviction to init the experiment.
+    bool rv = InitExperiment(&data_->header, mask_);
+    DCHECK(rv);
+  }
+
   Time create_time = Time::FromInternalValue(data_->header.create_time);
   CACHE_UMA(AGE, "FillupAge", 0, create_time);
 
diff --git a/net/disk_cache/eviction.cc b/net/disk_cache/eviction.cc
index 672ca61..fd24d02 100644
--- a/net/disk_cache/eviction.cc
+++ b/net/disk_cache/eviction.cc
@@ -237,6 +237,7 @@ void Eviction::ReportTrimTimes(EntryImpl* entry) {
     if (header_->create_time) {
       // This is the first entry that we have to evict, generate some noise.
       backend_->FirstEviction();
+      in_experiment_ = (header_->experiment == EXPERIMENT_DELETED_LIST_IN);
     } else {
       // This is an old file, but we may want more reports from this user so
       // lets save some create_time.
diff --git a/net/disk_cache/experiments.h b/net/disk_cache/experiments.h
index 5ca24db..c4e8ccb 100644
--- a/net/disk_cache/experiments.h
+++ b/net/disk_cache/experiments.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -17,7 +17,8 @@ enum {
   EXPERIMENT_OLD_FILE2 = 4,
   EXPERIMENT_DELETED_LIST_OUT = 11,
   EXPERIMENT_DELETED_LIST_CONTROL = 12,
-  EXPERIMENT_DELETED_LIST_IN = 13
+  EXPERIMENT_DELETED_LIST_IN = 13,
+  EXPERIMENT_DELETED_LIST_OUT2 = 14
 };
 
 }  // namespace disk_cache