eden: add experimental:enable-blob-caching

Summary: Adding an experimental option to EdenFS so we can disable blob caching if we need.

Reviewed By: chadaustin

Differential Revision: D18441665

fbshipit-source-id: 56751c0199d6658bfbf7ec3865f746a7279324ab

eden/fs/config/EdenConfig.h

@@ -300,6 +300,13 @@ class EdenConfig : private ConfigSettingManager {
   ConfigSetting<std::string> scribeCategory{"telemetry:scribe-category",
                                             "",
                                             this};
+
+  /**
+   * Controls whether if EdenFS caches blobs in local store.
+   */
+  ConfigSetting<bool> enableBlobCaching{"experimental:enable-blob-caching",
+                                        true,
+                                        this};
 };
 } // namespace eden
 } // namespace facebook

eden/fs/service/EdenServer.cpp

@@ -8,6 +8,7 @@
 #include "eden/fs/service/EdenServer.h"
 
 #include <cpptoml.h> // @manual=fbsource//third-party/cpptoml:cpptoml
+#include <atomic>
 #include <fstream>
 #include <memory>
 #include <sstream>
@@ -623,6 +624,9 @@ void EdenServer::openStorageEngine(
     ensureDirectoryExists(rocksPath);
     localStore_ = make_shared<RocksDbLocalStore>(
         rocksPath, &serverState_->getFaultInjector());
+    localStore_->enableBlobCaching.store(
+        serverState_->getEdenConfig()->enableBlobCaching.getValue(),
+        std::memory_order_relaxed);
     logger->log(
         "Opened RocksDB store in ",
         watch.elapsed().count() / 1000.0,

eden/fs/store/LocalStore.cpp

@@ -190,6 +190,11 @@ BlobMetadata LocalStore::getMetadataFromBlob(const Blob* blob) {
 }
 
 void LocalStore::putBlobWithoutMetadata(const Hash& id, const Blob* blob) {
+  if (!enableBlobCaching) {
+    XLOG(DBG4) << "Skipping caching " << id
+               << " because blob cache is diabled via config";
+    return;
+  }
   // Since blob serialization is moderately complex, just delegate
   // the immediate putBlob to the method on the WriteBatch.
   // Pre-allocate a buffer of approximately the right size; it

eden/fs/store/LocalStore.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <folly/Range.h>
+#include <atomic>
 #include <memory>
 #include <optional>
 #include "eden/fs/store/BlobMetadata.h"
@@ -275,6 +276,15 @@ class LocalStore : public std::enable_shared_from_this<LocalStore> {
   virtual std::unique_ptr<WriteBatch> beginWrite(size_t bufSize = 0) = 0;
 
   virtual void periodicManagementTask(const EdenConfig& config);
+
+  /*
+   * We keep this field to avoid making `LocalStore` holding a reference to
+   * `EdenConfig`, which will require us to change all the subclasses. We update
+   * this flag through `periodicManagementTask` function. The implication is
+   * that the configuration may need up to 1 minute to propagate (or whatever
+   * the configured local store management interval is).
+   */
+  std::atomic<bool> enableBlobCaching = true;
 };
 } // namespace eden
 } // namespace facebook

eden/fs/store/RocksDbLocalStore.cpp

@@ -8,6 +8,7 @@
 #include "eden/fs/store/RocksDbLocalStore.h"
 
 #include <array>
+#include <atomic>
 
 #include <fb303/ServiceData.h>
 #include <folly/Format.h>
@@ -557,6 +558,9 @@ uint64_t RocksDbLocalStore::getApproximateSize(
 }
 
 void RocksDbLocalStore::periodicManagementTask(const EdenConfig& config) {
+  enableBlobCaching.store(
+      config.enableBlobCaching.getValue(), std::memory_order_relaxed);
+
   // Compute and publish the stats
   auto ephemeralSize = publishStats();