IoUringBackend free mempool rework

Summary: IoUringBackend free mempool rework

Reviewed By: kevin-vigor

Differential Revision: D22424753

fbshipit-source-id: 5f8482702ec17561058ea841493e8a5a57b642a6

folly/experimental/io/IoUringBackend.cpp

@@ -113,27 +113,14 @@ IoUringBackend::IoUringBackend(Options options)
 
   numEntries_ *= 2;
 
-  entries_.reset(new IoSqe[numEntries_]);
-
   // timer entry
-  timerEntry_ = &entries_[0];
-  timerEntry_->backend_ = this;
+  timerEntry_ = std::make_unique<IoSqe>(this, false);
   timerEntry_->backendCb_ = PollIoBackend::processTimerIoCb;
 
   // signal entry
-  signalReadEntry_ = &entries_[1];
-  signalReadEntry_->backend_ = this;
+  signalReadEntry_ = std::make_unique<IoSqe>(this, false);
   signalReadEntry_->backendCb_ = PollIoBackend::processSignalReadIoCb;
 
-  // build the free list - first 2 entres are reserved
-  for (size_t i = 2; i < numEntries_; ++i) {
-    entries_[i].next_ = (i == (numEntries_ - 1)) ? nullptr : &entries_[i + 1];
-    entries_[i].backend_ = this;
-    entries_[i].backendCb_ = PollIoBackend::processPollIoCb;
-  }
-
-  freeHead_ = &entries_[2];
-
   // we need to call the init before adding the timer fd
   // so we avoid a deadlock - waiting for the queue to be drained
   if (options.useRegisteredFds) {
@@ -146,7 +133,6 @@ IoUringBackend::IoUringBackend(Options options)
   // add the timer fd
   if (!addTimerFd() || !addSignalFds()) {
     cleanup();
-    entries_.reset();
     throw NotAvailable("io_uring_submit error");
   }
 }
@@ -184,6 +170,15 @@ void IoUringBackend::cleanup() {
       }
     }
 
+    // free the entries
+    timerEntry_.reset();
+    signalReadEntry_.reset();
+    while (!freeList_.empty()) {
+      auto* ioCb = &freeList_.front();
+      freeList_.pop_front();
+      delete ioCb;
+    }
+
     // exit now
     ::io_uring_queue_exit(&ioRing_);
     ioRing_.ring_fd = -1;

folly/experimental/io/IoUringBackend.h

@@ -122,7 +122,7 @@ class IoUringBackend : public PollIoBackend {
   int submitBusyCheck(int num, WaitForEventsMode waitForEvents);
 
   struct IoSqe : public PollIoBackend::IoCb {
-    explicit IoSqe(PollIoBackend* backend = nullptr, bool poolAlloc = true)
+    explicit IoSqe(PollIoBackend* backend = nullptr, bool poolAlloc = false)
         : PollIoBackend::IoCb(backend, poolAlloc) {}
     ~IoSqe() override = default;
 
@@ -386,7 +386,8 @@ class IoUringBackend : public PollIoBackend {
   }
 
   PollIoBackend::IoCb* allocNewIoCb(const EventCallback& /*cb*/) override {
-    auto* ret = new IoSqe(this, false);
+    // allow pool alloc if numIoCbInUse_ < numEntries_
+    auto* ret = new IoSqe(this, numIoCbInUse_ < numEntries_);
     ret->backendCb_ = PollIoBackend::processPollIoCb;
 
     return ret;
@@ -396,8 +397,6 @@ class IoUringBackend : public PollIoBackend {
 
   size_t submit_internal();
 
-  std::unique_ptr<IoSqe[]> entries_;
-
   // io_uring related
   struct io_uring_params params_;
   struct io_uring ioRing_;

folly/experimental/io/PollIoBackend.cpp

@@ -150,13 +150,17 @@ PollIoBackend::PollIoBackend(Options options)
 }
 
 PollIoBackend::~PollIoBackend() {
+  CHECK(!timerEntry_);
+  CHECK(!signalReadEntry_);
+  CHECK(freeList_.empty());
+
   ::close(timerFd_);
 }
 
 bool PollIoBackend::addTimerFd() {
   auto* entry = allocSubmissionEntry(); // this can be nullptr
   timerEntry_->prepPollAdd(entry, timerFd_, POLLIN, true /*registerFd*/);
-  return (1 == submitOne(timerEntry_));
+  return (1 == submitOne(timerEntry_.get()));
 }
 
 bool PollIoBackend::addSignalFds() {
@@ -164,7 +168,7 @@ bool PollIoBackend::addSignalFds() {
   signalReadEntry_->prepPollAdd(
       entry, signalFds_.readFd(), POLLIN, false /*registerFd*/);
 
-  return (1 == submitOne(signalReadEntry_));
+  return (1 == submitOne(signalReadEntry_.get()));
 }
 
 void PollIoBackend::scheduleTimeout() {
@@ -336,9 +340,9 @@ size_t PollIoBackend::processSignals() {
 
 PollIoBackend::IoCb* PollIoBackend::allocIoCb(const EventCallback& cb) {
   // try to allocate from the pool first
-  if ((cb.type_ == EventCallback::Type::TYPE_NONE) && (freeHead_ != nullptr)) {
-    auto* ret = freeHead_;
-    freeHead_ = freeHead_->next_;
+  if ((cb.type_ == EventCallback::Type::TYPE_NONE) && (!freeList_.empty())) {
+    auto* ret = &freeList_.front();
+    freeList_.pop_front();
     numIoCbInUse_++;
     return ret;
   }
@@ -364,8 +368,7 @@ void PollIoBackend::releaseIoCb(PollIoBackend::IoCb* aioIoCb) {
 
   if (FOLLY_LIKELY(aioIoCb->poolAlloc_)) {
     aioIoCb->event_ = nullptr;
-    aioIoCb->next_ = freeHead_;
-    freeHead_ = aioIoCb;
+    freeList_.push_front(*aioIoCb);
   } else {
     delete aioIoCb;
   }

folly/experimental/io/PollIoBackend.h

@@ -117,7 +117,6 @@ class PollIoBackend : public EventBaseBackendBase {
     PollIoBackend* backend_;
     BackendCb* backendCb_{nullptr};
     const bool poolAlloc_;
-    IoCb* next_{nullptr}; // this is for the free list
     Event* event_{nullptr};
     FdRegistrationRecord* fdRecord_{nullptr};
     size_t useCount_{0};
@@ -357,9 +356,9 @@ class PollIoBackend : public EventBaseBackendBase {
 
   Options options_;
   size_t numEntries_;
-  IoCb* timerEntry_{nullptr};
-  IoCb* signalReadEntry_{nullptr};
-  IoCb* freeHead_{nullptr};
+  std::unique_ptr<IoCb> timerEntry_;
+  std::unique_ptr<IoCb> signalReadEntry_;
+  IoCbList freeList_;
 
   // timer related
   int timerFd_{-1};