[Feed] Disable read cache for LevelDB usages

This is an attempt to reduce the memory footprint LevelDB has on the
Feed experiment. This will reduce performance, but also reduce the
impact Feed has on memory usage. We want to prioritize memory here.

Bug: 914597
Change-Id: I42e36b126606cadd5212dab620aef867acdc8f76
Reviewed-on: https://chromium-review.googlesource.com/c/1387948
Commit-Queue: Brandon Wylie <wylieb@chromium.org>
Reviewed-by: Sky Malice <skym@chromium.org>
Reviewed-by: Filip Gorski <fgorski@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629827}

components/feed/core/feed_content_database.cc

@@ -36,6 +36,12 @@ const char kContentDatabaseFolder[] = "content";
 const size_t kDatabaseWriteBufferSizeBytes = 64 * 1024;                 // 64KB
 const size_t kDatabaseWriteBufferSizeBytesForLowEndDevice = 32 * 1024;  // 32KB
 
+leveldb::ReadOptions CreateReadOptions() {
+  leveldb::ReadOptions opts;
+  opts.fill_cache = false;
+  return opts;
+}
+
 bool DatabaseKeyFilter(const std::unordered_set<std::string>& key_set,
                        const std::string& key) {
   return key_set.find(key) != key_set.end();
@@ -97,6 +103,7 @@ void FeedContentDatabase::LoadContent(const std::vector<std::string>& keys,
 
   storage_database_->LoadEntriesWithFilter(
       base::BindRepeating(&DatabaseKeyFilter, std::move(key_set)),
+      CreateReadOptions(), /* target_prefix */ "",
       base::BindOnce(&FeedContentDatabase::OnLoadEntriesForLoadContent,
                      weak_ptr_factory_.GetWeakPtr(), base::TimeTicks::Now(),
                      std::move(callback)));
@@ -108,6 +115,7 @@ void FeedContentDatabase::LoadContentByPrefix(const std::string& prefix,
 
   storage_database_->LoadEntriesWithFilter(
       base::BindRepeating(&DatabasePrefixFilter, std::move(prefix)),
+      CreateReadOptions(), /* target_prefix */ "",
       base::BindOnce(&FeedContentDatabase::OnLoadEntriesForLoadContent,
                      weak_ptr_factory_.GetWeakPtr(), base::TimeTicks::Now(),
                      std::move(callback)));

components/image_fetcher/core/cache/image_metadata_store_leveldb.cc

@@ -23,6 +23,12 @@ namespace image_fetcher {
 
 namespace {
 
+leveldb::ReadOptions CreateReadOptions() {
+  leveldb::ReadOptions opts;
+  opts.fill_cache = false;
+  return opts;
+}
+
 int64_t ToDatabaseTime(base::Time time) {
   return time.since_origin().InMicroseconds();
 }
@@ -143,7 +149,8 @@ void ImageMetadataStoreLevelDB::UpdateImageMetadata(const std::string& key) {
   }
 
   database_->LoadEntriesWithFilter(
-      base::BindRepeating(&KeyMatcherFilter, key),
+      base::BindRepeating(&KeyMatcherFilter, key), CreateReadOptions(),
+      /* target_prefix */ "",
       base::BindOnce(&ImageMetadataStoreLevelDB::UpdateImageMetadataImpl,
                      weak_ptr_factory_.GetWeakPtr()));
 }