mirror of
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128 lines
3.4 KiB
Go
128 lines
3.4 KiB
Go
package fs
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import (
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"flag"
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"fmt"
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"os"
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"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
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"github.com/VictoriaMetrics/metrics"
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"golang.org/x/sys/unix"
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)
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var disableMmap = flag.Bool("fs.disableMmap", false, "Whether to use pread() instead of mmap() for reading data files")
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// MustReadAtCloser is rand-access read interface.
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type MustReadAtCloser interface {
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// MustReadAt must read len(p) bytes from offset off to p.
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MustReadAt(p []byte, off int64)
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// MustClose must close the reader.
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MustClose()
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}
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// ReaderAt implements rand-access reader.
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type ReaderAt struct {
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f *os.File
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mmapData []byte
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}
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// MustReadAt reads len(p) bytes at off from r.
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func (r *ReaderAt) MustReadAt(p []byte, off int64) {
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if len(p) == 0 {
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return
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}
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if len(r.mmapData) == 0 || len(p) > 8*1024*1024 {
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// Read big blocks directly from file.
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// This could be faster than reading these blocks from mmap,
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// since it triggers less page faults.
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n, err := r.f.ReadAt(p, off)
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if err != nil {
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logger.Panicf("FATAL: cannot read %d bytes at offset %d of file %q: %s", len(p), off, r.f.Name(), err)
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}
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if n != len(p) {
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logger.Panicf("FATAL: unexpected number of bytes read; got %d; want %d", n, len(p))
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}
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} else {
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if off < 0 || off > int64(len(r.mmapData)-len(p)) {
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logger.Panicf("off=%d is out of allowed range [0...%d] for len(p)=%d", off, len(r.mmapData)-len(p), len(p))
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}
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copyMmap(p, r.mmapData[off:])
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}
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readCalls.Inc()
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readBytes.Add(len(p))
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}
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// MustClose closes r.
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func (r *ReaderAt) MustClose() {
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fname := r.f.Name()
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if len(r.mmapData) > 0 {
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if err := unix.Munmap(r.mmapData); err != nil {
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logger.Panicf("FATAL: cannot unmap data for file %q: %s", fname, err)
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}
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r.mmapData = nil
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}
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MustClose(r.f)
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r.f = nil
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readersCount.Dec()
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}
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// MustFadviseSequentialRead hints the OS that f is read mostly sequentially.
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//
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// if prefetch is set, then the OS is hinted to prefetch f data.
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func (r *ReaderAt) MustFadviseSequentialRead(prefetch bool) {
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if err := fadviseSequentialRead(r.f, prefetch); err != nil {
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logger.Panicf("FATAL: error in fadviseSequentialRead(%q, %v): %s", r.f.Name(), prefetch, err)
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}
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}
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// OpenReaderAt opens ReaderAt for reading from filename.
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//
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// MustClose must be called on the returned ReaderAt when it is no longer needed.
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func OpenReaderAt(path string) (*ReaderAt, error) {
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f, err := os.Open(path)
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if err != nil {
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return nil, fmt.Errorf("cannot open file %q for reader: %s", path, err)
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}
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var r ReaderAt
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r.f = f
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if !*disableMmap {
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data, err := mmapFile(f)
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if err != nil {
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MustClose(f)
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return nil, fmt.Errorf("cannot init reader for %q: %s", path, err)
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}
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r.mmapData = data
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}
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r.MustFadviseSequentialRead(false)
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readersCount.Inc()
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return &r, nil
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}
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var (
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readCalls = metrics.NewCounter(`vm_fs_read_calls_total`)
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readBytes = metrics.NewCounter(`vm_fs_read_bytes_total`)
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readersCount = metrics.NewCounter(`vm_fs_readers`)
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)
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func mmapFile(f *os.File) ([]byte, error) {
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fi, err := f.Stat()
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if err != nil {
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return nil, fmt.Errorf("error in stat: %s", err)
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}
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size := fi.Size()
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if size == 0 {
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return nil, nil
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}
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if size < 0 {
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return nil, fmt.Errorf("got negative file size: %d bytes", size)
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}
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if int64(int(size)) != size {
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return nil, fmt.Errorf("file is too big to be mmap'ed: %d bytes", size)
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}
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data, err := unix.Mmap(int(f.Fd()), 0, int(size), unix.PROT_READ, unix.MAP_SHARED)
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if err != nil {
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return nil, fmt.Errorf("cannot mmap file with size %d: %s", size, err)
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}
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return data, nil
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}
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