[3.6.fb] use fallocate(FALLOC_FL_PUNCH_HOLE) to release unused blocks at the end of file
Summary: ftruncate does not always free preallocated unused space at the end of file. In some cases, we pin too much disk space than it should This is a fix previously reviewed in on https://reviews.facebook.net/D25641 Test Plan: env_test Reviewers: igor, ljin, sdong Subscribers: dhruba Differential Revision: https://reviews.facebook.net/D27975
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@ -736,15 +736,29 @@ class PosixWritableFile : public WritableFile {
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GetPreallocationStatus(&block_size, &last_allocated_block);
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GetPreallocationStatus(&block_size, &last_allocated_block);
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if (last_allocated_block > 0) {
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if (last_allocated_block > 0) {
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// trim the extra space preallocated at the end of the file
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// trim the extra space preallocated at the end of the file
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int dummy __attribute__((unused));
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// NOTE(ljin): we probably don't want to surface failure as an IOError,
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dummy = ftruncate(fd_, filesize_); // ignore errors
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// but it will be nice to log these errors.
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ftruncate(fd_, filesize_);
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#ifdef ROCKSDB_FALLOCATE_PRESENT
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// in some file systems, ftruncate only trims trailing space if the
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// new file size is smaller than the current size. Calling fallocate
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// with FALLOC_FL_PUNCH_HOLE flag to explicitly release these unused
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// blocks. FALLOC_FL_PUNCH_HOLE is supported on at least the following
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// filesystems:
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// XFS (since Linux 2.6.38)
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// ext4 (since Linux 3.0)
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// Btrfs (since Linux 3.7)
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// tmpfs (since Linux 3.5)
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// We ignore error since failure of this operation does not affect
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// correctness.
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fallocate(fd_, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
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filesize_, block_size * last_allocated_block - filesize_);
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#endif
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}
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}
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if (close(fd_) < 0) {
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if (close(fd_) < 0) {
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if (s.ok()) {
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s = IOError(filename_, errno);
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s = IOError(filename_, errno);
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}
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}
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}
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fd_ = -1;
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fd_ = -1;
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return s;
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return s;
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}
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}
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@ -516,7 +516,7 @@ TEST(EnvPosixTest, AllocateTest) {
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// allocate 100 MB
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// allocate 100 MB
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size_t kPreallocateSize = 100 * 1024 * 1024;
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size_t kPreallocateSize = 100 * 1024 * 1024;
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size_t kBlockSize = 512;
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size_t kBlockSize = 512;
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std::string data = "test";
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std::string data(1024 * 1024, 'a');
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wfile->SetPreallocationBlockSize(kPreallocateSize);
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wfile->SetPreallocationBlockSize(kPreallocateSize);
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ASSERT_OK(wfile->Append(Slice(data)));
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ASSERT_OK(wfile->Append(Slice(data)));
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ASSERT_OK(wfile->Flush());
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ASSERT_OK(wfile->Flush());
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@ -538,7 +538,7 @@ TEST(EnvPosixTest, AllocateTest) {
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stat(fname.c_str(), &f_stat);
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stat(fname.c_str(), &f_stat);
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ASSERT_EQ((unsigned int)data.size(), f_stat.st_size);
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ASSERT_EQ((unsigned int)data.size(), f_stat.st_size);
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// verify that preallocated blocks were deallocated on file close
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// verify that preallocated blocks were deallocated on file close
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ASSERT_GT(st_blocks, f_stat.st_blocks);
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ASSERT_EQ((f_stat.st_size + kBlockSize - 1) / kBlockSize, f_stat.st_blocks);
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}
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}
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#endif // ROCKSDB_FALLOCATE_PRESENT
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#endif // ROCKSDB_FALLOCATE_PRESENT
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