overlay: allow creation of in-memory overlay

Summary: As we need to debugging a IO related performance issue. We want to see if writes in overlay has caused any issues. This diff adds an option to allow us to create in-memory overlays.

Reviewed By: chadaustin

Differential Revision: D28951905

fbshipit-source-id: 9ef1da183771ee69b855b49bbabc2ef02a7ec9ac

eden/fs/config/EdenConfig.h

@@ -616,6 +616,16 @@ class EdenConfig : private ConfigSettingManager {
       "overlay:enable_tree_overlay",
       false,
       this};
+
+  /**
+   * DANGER: this option is to help investigating performances issues with
+   * EdenFS. Turning this option on in non-debugging environment will result
+   * data loss.
+   */
+  ConfigSetting<bool> unsafeInMemoryOverlay{
+      "overlay:unsafe-in-memory-overlay",
+      false,
+      this};
 };
 } // namespace eden
 } // namespace facebook

eden/fs/inodes/EdenMount.cpp

@@ -210,8 +210,7 @@ EdenMount::EdenMount(
       overlay_{Overlay::create(
           checkoutConfig_->getOverlayPath(),
           checkoutConfig_->getCaseSensitive(),
-          static_cast<Overlay::OverlayType>(
-              checkoutConfig_->getEnableTreeOverlay()),
+          getOverlayType(),
           serverState_->getStructuredLogger())},
 #ifndef _WIN32
       overlayFileAccess_{overlay_.get()},
@@ -225,6 +224,17 @@ EdenMount::EdenMount(
       clock_{serverState_->getClock()} {
 }
 
+Overlay::OverlayType EdenMount::getOverlayType() {
+  if (checkoutConfig_->getEnableTreeOverlay()) {
+    if (getEdenConfig()->unsafeInMemoryOverlay.getValue()) {
+      return Overlay::OverlayType::TreeInMemory;
+    }
+    return Overlay::OverlayType::Tree;
+  } else {
+    return Overlay::OverlayType::Legacy;
+  }
+}
+
 FOLLY_NODISCARD folly::Future<folly::Unit> EdenMount::initialize(
     OverlayChecker::ProgressCallback&& progressCallback,
     const std::optional<SerializedInodeMap>& takeover) {

eden/fs/inodes/EdenMount.h

@@ -697,6 +697,11 @@ class EdenMount {
    */
   void transitionToFuseInitializationErrorState();
 
+  /**
+   * Returns overlay type based on settings.
+   */
+  Overlay::OverlayType getOverlayType();
+
   EdenMount(
       std::unique_ptr<CheckoutConfig> checkoutConfig,
       std::shared_ptr<ObjectStore> objectStore,

eden/fs/inodes/Overlay.cpp

@@ -23,6 +23,7 @@
 #include "eden/fs/inodes/InodeBase.h"
 #include "eden/fs/inodes/TreeInode.h"
 #include "eden/fs/inodes/treeoverlay/TreeOverlay.h"
+#include "eden/fs/sqlite/SqliteDatabase.h"
 #include "eden/fs/utils/Bug.h"
 #include "eden/fs/utils/PathFuncs.h"
 
@@ -43,6 +44,10 @@ std::unique_ptr<IOverlay> makeOverlay(
     Overlay::OverlayType overlayType) {
   if (overlayType == Overlay::OverlayType::Tree) {
     return std::make_unique<TreeOverlay>(localDir);
+  } else if (overlayType == Overlay::OverlayType::TreeInMemory) {
+    XLOG(WARN) << "In-memory overlay requested. This will cause data loss.";
+    return std::make_unique<TreeOverlay>(
+        std::make_unique<SqliteDatabase>(SqliteDatabase::inMemory));
   }
 #ifdef _WIN32
   return std::make_unique<SqliteOverlay>(localDir);

eden/fs/inodes/Overlay.h

@@ -70,7 +70,11 @@ class OverlayFile;
  */
 class Overlay : public std::enable_shared_from_this<Overlay> {
  public:
-  enum class OverlayType : bool { Legacy = false, Tree = true };
+  enum class OverlayType : uint8_t {
+    Legacy = 0,
+    Tree = 1,
+    TreeInMemory = 2,
+  };
 
   /**
    * Create a new Overlay object.

eden/fs/inodes/treeoverlay/TreeOverlay.h

@@ -28,6 +28,9 @@ class TreeOverlay : public IOverlay {
  public:
   explicit TreeOverlay(AbsolutePathPiece path);
 
+  explicit TreeOverlay(std::unique_ptr<SqliteDatabase> store)
+      : store_(std::move(store)) {}
+
   ~TreeOverlay() override {}
 
   TreeOverlay(const TreeOverlay&) = delete;