Use fallocate for file size extension when supported (facebookincubat…

…or#11403)

Summary:
Pull Request resolved: facebookincubator#11403

When Copy-on-Write (COW) is disabled on Btrfs, automatic relocation
creates snapshots of files, ignoring the noCOW setting. This results
in increased disk usage and can lead to "no space left" errors in
production.

One possible enhancement we can make is to use `fallocate` to reserve
space immediately after file creation. This helps ensure the allocated
space is as continuous as possible.

Reviewed By: xiaoxmeng

Differential Revision: D65316028

fbshipit-source-id: f690fb454d40b45c005358c85d5389b75e7ebe77

velox/common/caching/SsdFile.cpp

@@ -169,11 +169,15 @@ SsdFile::SsdFile(const Config& config)
   writeFile_ = fs_->openFileForWrite(fileName_, fileOptions);
   readFile_ = fs_->openFileForRead(fileName_);
 
-  const uint64_t size = writeFile_->size();
-  numRegions_ = std::min<int32_t>(size / kRegionSize, maxRegions_);
-  fileSize_ = numRegions_ * kRegionSize;
-  if ((size % kRegionSize > 0) || (size > numRegions_ * kRegionSize)) {
-    writeFile_->truncate(fileSize_);
+  // NOTE: checkpoint recovery will set 'numRegions_' and 'dataSize_'
+  // accordingly.
+  numRegions_ = 0;
+  dataSize_ = 0;
+
+  const auto maxFileSize = kRegionSize * maxRegions_;
+  if (writeFile_->size() != maxFileSize) {
+    // Initialize and pre-allocate (if possible) the data file with fixed space.
+    writeFile_->truncate(static_cast<int64_t>(maxFileSize));
   }
   // The existing regions in the file are writable.
   writableRegions_.resize(numRegions_);
@@ -334,10 +338,8 @@ std::optional<std::pair<uint64_t, int32_t>> SsdFile::getSpace(
 bool SsdFile::growOrEvictLocked() {
   process::TraceContext trace("SsdFile::growOrEvictLocked");
   if (numRegions_ < maxRegions_) {
-    const auto newSize = (numRegions_ + 1) * kRegionSize;
     try {
-      writeFile_->truncate(newSize);
-      fileSize_ = newSize;
+      dataSize_ = (numRegions_ + 1) * kRegionSize;
       writableRegions_.push_back(numRegions_);
       regionSizes_[numRegions_] = 0;
       erasedRegionSizes_[numRegions_] = 0;
@@ -448,7 +450,7 @@ void SsdFile::write(std::vector<CachePin>& pins) {
       writeOffset += writeLength;
       writeLength = 0;
     }
-    VELOX_CHECK_GE(fileSize_, writeOffset);
+    VELOX_CHECK_GE(dataSize_, writeOffset);
 
     {
       std::lock_guard<std::shared_mutex> l(mutex_);
@@ -1007,6 +1009,7 @@ void SsdFile::readCheckpoint(std::ifstream& state) {
       maxRegions_,
       "Trying to start from checkpoint with a different capacity");
   numRegions_ = readNumber<int32_t>(state);
+  dataSize_ = numRegions_ * kRegionSize;
   std::vector<double> scores(maxRegions);
   state.read(asChar(scores.data()), maxRegions_ * sizeof(double));
   std::unordered_map<uint64_t, StringIdLease> idMap;

velox/common/caching/SsdFile.h

@@ -563,8 +563,8 @@ class SsdFile {
   // File system.
   std::shared_ptr<filesystems::FileSystem> fs_;
 
-  // Size of the backing file in bytes. Must be multiple of kRegionSize.
-  uint64_t fileSize_{0};
+  // The size of actual cached data in bytes. Must be multiple of kRegionSize.
+  uint64_t dataSize_{0};
 
   // ReadFile for cache data file.
   std::unique_ptr<ReadFile> readFile_;

velox/common/caching/tests/SsdFileTest.cpp

@@ -647,7 +647,7 @@ TEST_F(SsdFileTest, recoverFromCheckpointWithChecksum) {
       ASSERT_EQ(statsAfterRecover.entriesCached, stats.entriesCached);
     } else {
       ASSERT_EQ(statsAfterRecover.bytesCached, 0);
-      ASSERT_EQ(statsAfterRecover.regionsCached, stats.regionsCached);
+      ASSERT_EQ(statsAfterRecover.regionsCached, 0);
       ASSERT_EQ(statsAfterRecover.entriesCached, 0);
     }
 

velox/common/file/File.cpp

@@ -377,6 +377,21 @@ void LocalWriteFile::write(
 void LocalWriteFile::truncate(int64_t newSize) {
   checkNotClosed(closed_);
   VELOX_CHECK_GE(newSize, 0, "New size cannot be negative.");
+#ifdef linux
+  if (newSize > size_) {
+    // Use fallocate to extend the file.
+    const auto ret = ::fallocate(fd_, 0, 0, newSize);
+    VELOX_CHECK_EQ(
+        ret,
+        0,
+        "fallocate failed in LocalWriteFile::truncate: {}.",
+        folly::errnoStr(errno));
+    size_ = newSize;
+    return;
+  }
+#endif // linux
+
+  // Fallback to ftruncate.
   const auto ret = ::ftruncate(fd_, newSize);
   VELOX_CHECK_EQ(
       ret,