From 646c3588de84ac532a0e3525eae03edae1ea759f Mon Sep 17 00:00:00 2001 From: cmumford Date: Tue, 3 Jan 2017 17:39:49 -0800 Subject: [PATCH] Limit the number of read-only files the POSIX Env will have open. Background compaction can create an unbounded number of leveldb::RandomAccessFile instances. On 64-bit systems mmap is used and file descriptors are only used beyond a certain number of mmap's. 32-bit systems to not use mmap at all. leveldb::RandomAccessFile does not observe Options.max_open_files so compaction could exhaust the file descriptor limit. This change uses getrlimit to determine the maximum number of open files and limits RandomAccessFile to approximately 20% of that value. ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=143505556 --- util/env_posix.cc | 192 ++++++++++++++++++++++++----------- util/env_posix_test_helper.h | 28 +++++ util/env_test.cc | 42 ++++++++ 3 files changed, 204 insertions(+), 58 deletions(-) create mode 100644 util/env_posix_test_helper.h diff --git a/util/env_posix.cc b/util/env_posix.cc index a17dec278f4c3..342a2ff9aa49b 100644 --- a/util/env_posix.cc +++ b/util/env_posix.cc @@ -10,6 +10,7 @@ #include #include #include +#include #include #include #include @@ -23,15 +24,70 @@ #include "util/logging.h" #include "util/mutexlock.h" #include "util/posix_logger.h" +#include "util/env_posix_test_helper.h" namespace leveldb { namespace { +static int open_read_only_file_limit = -1; +static int mmap_limit = -1; + static Status IOError(const std::string& context, int err_number) { return Status::IOError(context, strerror(err_number)); } +// Helper class to limit resource usage to avoid exhaustion. +// Currently used to limit read-only file descriptors and mmap file usage +// so that we do not end up running out of file descriptors, virtual memory, +// or running into kernel performance problems for very large databases. +class Limiter { + public: + // Limit maximum number of resources to |n|. + Limiter(intptr_t n) { + SetAllowed(n); + } + + // If another resource is available, acquire it and return true. + // Else return false. + bool Acquire() { + if (GetAllowed() <= 0) { + return false; + } + MutexLock l(&mu_); + intptr_t x = GetAllowed(); + if (x <= 0) { + return false; + } else { + SetAllowed(x - 1); + return true; + } + } + + // Release a resource acquired by a previous call to Acquire() that returned + // true. + void Release() { + MutexLock l(&mu_); + SetAllowed(GetAllowed() + 1); + } + + private: + port::Mutex mu_; + port::AtomicPointer allowed_; + + intptr_t GetAllowed() const { + return reinterpret_cast(allowed_.Acquire_Load()); + } + + // REQUIRES: mu_ must be held + void SetAllowed(intptr_t v) { + allowed_.Release_Store(reinterpret_cast(v)); + } + + Limiter(const Limiter&); + void operator=(const Limiter&); +}; + class PosixSequentialFile: public SequentialFile { private: std::string filename_; @@ -69,73 +125,51 @@ class PosixSequentialFile: public SequentialFile { class PosixRandomAccessFile: public RandomAccessFile { private: std::string filename_; + bool temporary_fd_; // If true, fd_ is -1 and we open on every read. int fd_; + Limiter* limiter_; public: - PosixRandomAccessFile(const std::string& fname, int fd) - : filename_(fname), fd_(fd) { } - virtual ~PosixRandomAccessFile() { close(fd_); } + PosixRandomAccessFile(const std::string& fname, int fd, Limiter* limiter) + : filename_(fname), fd_(fd), limiter_(limiter) { + temporary_fd_ = !limiter->Acquire(); + if (temporary_fd_) { + // Open file on every access. + close(fd_); + fd_ = -1; + } + } + + virtual ~PosixRandomAccessFile() { + if (!temporary_fd_) { + close(fd_); + limiter_->Release(); + } + } virtual Status Read(uint64_t offset, size_t n, Slice* result, char* scratch) const { + int fd = fd_; + if (temporary_fd_) { + fd = open(filename_.c_str(), O_RDONLY); + if (fd < 0) { + return IOError(filename_, errno); + } + } + Status s; - ssize_t r = pread(fd_, scratch, n, static_cast(offset)); + ssize_t r = pread(fd, scratch, n, static_cast(offset)); *result = Slice(scratch, (r < 0) ? 0 : r); if (r < 0) { // An error: return a non-ok status s = IOError(filename_, errno); } - return s; - } -}; - -// Helper class to limit mmap file usage so that we do not end up -// running out virtual memory or running into kernel performance -// problems for very large databases. -class MmapLimiter { - public: - // Up to 1000 mmaps for 64-bit binaries; none for smaller pointer sizes. - MmapLimiter() { - SetAllowed(sizeof(void*) >= 8 ? 1000 : 0); - } - - // If another mmap slot is available, acquire it and return true. - // Else return false. - bool Acquire() { - if (GetAllowed() <= 0) { - return false; - } - MutexLock l(&mu_); - intptr_t x = GetAllowed(); - if (x <= 0) { - return false; - } else { - SetAllowed(x - 1); - return true; + if (temporary_fd_) { + // Close the temporary file descriptor opened earlier. + close(fd); } + return s; } - - // Release a slot acquired by a previous call to Acquire() that returned true. - void Release() { - MutexLock l(&mu_); - SetAllowed(GetAllowed() + 1); - } - - private: - port::Mutex mu_; - port::AtomicPointer allowed_; - - intptr_t GetAllowed() const { - return reinterpret_cast(allowed_.Acquire_Load()); - } - - // REQUIRES: mu_ must be held - void SetAllowed(intptr_t v) { - allowed_.Release_Store(reinterpret_cast(v)); - } - - MmapLimiter(const MmapLimiter&); - void operator=(const MmapLimiter&); }; // mmap() based random-access @@ -144,12 +178,12 @@ class PosixMmapReadableFile: public RandomAccessFile { std::string filename_; void* mmapped_region_; size_t length_; - MmapLimiter* limiter_; + Limiter* limiter_; public: // base[0,length-1] contains the mmapped contents of the file. PosixMmapReadableFile(const std::string& fname, void* base, size_t length, - MmapLimiter* limiter) + Limiter* limiter) : filename_(fname), mmapped_region_(base), length_(length), limiter_(limiter) { } @@ -332,7 +366,7 @@ class PosixEnv : public Env { mmap_limit_.Release(); } } else { - *result = new PosixRandomAccessFile(fname, fd); + *result = new PosixRandomAccessFile(fname, fd, &fd_limit_); } return s; } @@ -532,10 +566,42 @@ class PosixEnv : public Env { BGQueue queue_; PosixLockTable locks_; - MmapLimiter mmap_limit_; + Limiter mmap_limit_; + Limiter fd_limit_; }; -PosixEnv::PosixEnv() : started_bgthread_(false) { +// Return the maximum number of concurrent mmaps. +static int MaxMmaps() { + if (mmap_limit >= 0) { + return mmap_limit; + } + // Up to 1000 mmaps for 64-bit binaries; none for smaller pointer sizes. + mmap_limit = sizeof(void*) >= 8 ? 1000 : 0; + return mmap_limit; +} + +// Return the maximum number of read-only files to keep open. +static intptr_t MaxOpenFiles() { + if (open_read_only_file_limit >= 0) { + return open_read_only_file_limit; + } + struct rlimit rlim; + if (getrlimit(RLIMIT_NOFILE, &rlim)) { + // getrlimit failed, fallback to hard-coded default. + open_read_only_file_limit = 50; + } else if (rlim.rlim_cur == RLIM_INFINITY) { + open_read_only_file_limit = std::numeric_limits::max(); + } else { + // Allow use of 20% of available file descriptors for read-only files. + open_read_only_file_limit = rlim.rlim_cur / 5; + } + return open_read_only_file_limit; +} + +PosixEnv::PosixEnv() + : started_bgthread_(false), + mmap_limit_(MaxMmaps()), + fd_limit_(MaxOpenFiles()) { PthreadCall("mutex_init", pthread_mutex_init(&mu_, NULL)); PthreadCall("cvar_init", pthread_cond_init(&bgsignal_, NULL)); } @@ -610,6 +676,16 @@ static pthread_once_t once = PTHREAD_ONCE_INIT; static Env* default_env; static void InitDefaultEnv() { default_env = new PosixEnv; } +void EnvPosixTestHelper::SetReadOnlyFDLimit(int limit) { + assert(default_env == NULL); + open_read_only_file_limit = limit; +} + +void EnvPosixTestHelper::SetReadOnlyMMapLimit(int limit) { + assert(default_env == NULL); + mmap_limit = limit; +} + Env* Env::Default() { pthread_once(&once, InitDefaultEnv); return default_env; diff --git a/util/env_posix_test_helper.h b/util/env_posix_test_helper.h new file mode 100644 index 0000000000000..0386960598260 --- /dev/null +++ b/util/env_posix_test_helper.h @@ -0,0 +1,28 @@ +// Copyright 2017 The LevelDB Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. See the AUTHORS file for names of contributors. + +#ifndef STORAGE_LEVELDB_UTIL_ENV_POSIX_TEST_HELPER_H_ +#define STORAGE_LEVELDB_UTIL_ENV_POSIX_TEST_HELPER_H_ + +namespace leveldb { + +class EnvPosixTest; + +// A helper for the POSIX Env to facilitate testing. +class EnvPosixTestHelper { + private: + friend class EnvPosixTest; + + // Set the maximum number of read-only files that will be opened. + // Must be called before creating an Env. + static void SetReadOnlyFDLimit(int limit); + + // Set the maximum number of read-only files that will be mapped via mmap. + // Must be called before creating an Env. + static void SetReadOnlyMMapLimit(int limit); +}; + +} // namespace leveldb + +#endif // STORAGE_LEVELDB_UTIL_ENV_POSIX_TEST_HELPER_H_ diff --git a/util/env_test.cc b/util/env_test.cc index b72cb4438425b..0cb1577bc3487 100644 --- a/util/env_test.cc +++ b/util/env_test.cc @@ -6,10 +6,13 @@ #include "port/port.h" #include "util/testharness.h" +#include "util/env_posix_test_helper.h" namespace leveldb { static const int kDelayMicros = 100000; +static const int kReadOnlyFileLimit = 4; +static const int kMMapLimit = 4; class EnvPosixTest { private: @@ -19,6 +22,11 @@ class EnvPosixTest { public: Env* env_; EnvPosixTest() : env_(Env::Default()) { } + + static void SetFileLimits(int read_only_file_limit, int mmap_limit) { + EnvPosixTestHelper::SetReadOnlyFDLimit(read_only_file_limit); + EnvPosixTestHelper::SetReadOnlyMMapLimit(mmap_limit); + } }; static void SetBool(void* ptr) { @@ -97,8 +105,42 @@ TEST(EnvPosixTest, StartThread) { ASSERT_EQ(state.val, 3); } +TEST(EnvPosixTest, TestOpenOnRead) { + // Write some test data to a single file that will be opened |n| times. + std::string test_dir; + ASSERT_OK(Env::Default()->GetTestDirectory(&test_dir)); + std::string test_file = test_dir + "/open_on_read.txt"; + + FILE* f = fopen(test_file.c_str(), "w"); + ASSERT_TRUE(f != NULL); + const char kFileData[] = "abcdefghijklmnopqrstuvwxyz"; + fputs(kFileData, f); + fclose(f); + + // Open test file some number above the sum of the two limits to force + // open-on-read behavior of POSIX Env leveldb::RandomAccessFile. + const int kNumFiles = kReadOnlyFileLimit + kMMapLimit + 5; + leveldb::RandomAccessFile* files[kNumFiles] = {0}; + for (int i = 0; i < kNumFiles; i++) { + ASSERT_OK(Env::Default()->NewRandomAccessFile(test_file, &files[i])); + } + char scratch; + Slice read_result; + for (int i = 0; i < kNumFiles; i++) { + ASSERT_OK(files[i]->Read(i, 1, &read_result, &scratch)); + ASSERT_EQ(kFileData[i], read_result[0]); + } + for (int i = 0; i < kNumFiles; i++) { + delete files[i]; + } + ASSERT_OK(Env::Default()->DeleteFile(test_file)); +} + } // namespace leveldb int main(int argc, char** argv) { + // All tests currently run with the same read-only file limits. + leveldb::EnvPosixTest::SetFileLimits(leveldb::kReadOnlyFileLimit, + leveldb::kMMapLimit); return leveldb::test::RunAllTests(); }