use O_DIRECT for all ReadFileStream (#13324)

This PR also removes #13312 to ensure
that we can use a better mechanism to
handle page-cache, using O_DIRECT
even for Range GETs.

internal/ioutil/ioutil.go

@@ -227,9 +227,9 @@ func SameFile(fi1, fi2 os.FileInfo) bool {
 	return true
 }
 
-// DirectIO alignment needs to be 4K. Defined here as
+// DirectioAlignSize - DirectIO alignment needs to be 4K. Defined here as
 // directio.AlignSize is defined as 0 in MacOS causing divide by 0 error.
-const directioAlignSize = 4096
+const DirectioAlignSize = 4096
 
 // CopyAligned - copies from reader to writer using the aligned input
 // buffer, it is expected that input buffer is page aligned to
@@ -269,7 +269,7 @@ func CopyAligned(w *os.File, r io.Reader, alignedBuf []byte, totalSize int64) (i
 		}
 		buf = buf[:nr]
 		var nw int64
-		if len(buf)%directioAlignSize == 0 {
+		if len(buf)%DirectioAlignSize == 0 {
 			var n int
 			// buf is aligned for directio write()
 			n, err = w.Write(buf)

internal/ioutil/odirect_reader.go

@@ -0,0 +1,131 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package ioutil
+
+import (
+	"errors"
+	"io"
+	"os"
+	"sync"
+	"syscall"
+
+	"github.com/dustin/go-humanize"
+	"github.com/minio/minio/internal/disk"
+)
+
+// ODirectReader - to support O_DIRECT reads for erasure backends.
+type ODirectReader struct {
+	File      *os.File
+	SmallFile bool
+	err       error
+	buf       []byte
+	bufp      *[]byte
+	seenRead  bool
+}
+
+// Block sizes constant.
+const (
+	BlockSizeSmall       = 128 * humanize.KiByte // Default r/w block size for smaller objects.
+	BlockSizeLarge       = 2 * humanize.MiByte   // Default r/w block size for larger objects.
+	BlockSizeReallyLarge = 4 * humanize.MiByte   // Default write block size for objects per shard >= 64MiB
+)
+
+// O_DIRECT aligned sync.Pool's
+var (
+	ODirectPoolXLarge = sync.Pool{
+		New: func() interface{} {
+			b := disk.AlignedBlock(BlockSizeReallyLarge)
+			return &b
+		},
+	}
+	ODirectPoolLarge = sync.Pool{
+		New: func() interface{} {
+			b := disk.AlignedBlock(BlockSizeLarge)
+			return &b
+		},
+	}
+	ODirectPoolSmall = sync.Pool{
+		New: func() interface{} {
+			b := disk.AlignedBlock(BlockSizeSmall)
+			return &b
+		},
+	}
+)
+
+// Invalid argument, unsupported flags such as O_DIRECT
+func isSysErrInvalidArg(err error) bool {
+	return errors.Is(err, syscall.EINVAL)
+}
+
+// Read - Implements Reader interface.
+func (o *ODirectReader) Read(buf []byte) (n int, err error) {
+	if o.err != nil && (len(o.buf) == 0 || !o.seenRead) {
+		return 0, o.err
+	}
+	if o.buf == nil {
+		if o.SmallFile {
+			o.bufp = ODirectPoolSmall.Get().(*[]byte)
+		} else {
+			o.bufp = ODirectPoolLarge.Get().(*[]byte)
+		}
+	}
+	if !o.seenRead {
+		o.buf = *o.bufp
+		n, err = o.File.Read(o.buf)
+		if err != nil && err != io.EOF {
+			if isSysErrInvalidArg(err) {
+				if err = disk.DisableDirectIO(o.File); err != nil {
+					o.err = err
+					return n, err
+				}
+				n, err = o.File.Read(o.buf)
+			}
+			if err != nil && err != io.EOF {
+				o.err = err
+				return n, err
+			}
+		}
+		if n == 0 {
+			// err is likely io.EOF
+			o.err = err
+			return n, err
+		}
+		o.err = err
+		o.buf = o.buf[:n]
+		o.seenRead = true
+	}
+	if len(buf) >= len(o.buf) {
+		n = copy(buf, o.buf)
+		o.seenRead = false
+		return n, o.err
+	}
+	n = copy(buf, o.buf)
+	o.buf = o.buf[n:]
+	// There is more left in buffer, do not return any EOF yet.
+	return n, nil
+}
+
+// Close - Release the buffer and close the file.
+func (o *ODirectReader) Close() error {
+	if o.SmallFile {
+		ODirectPoolSmall.Put(o.bufp)
+	} else {
+		ODirectPoolLarge.Put(o.bufp)
+	}
+	return o.File.Close()
+}

internal/ioutil/read_file.go

@@ -19,7 +19,6 @@ package ioutil
 
 import (
 	"io"
-	"os"
 
 	"github.com/minio/minio/internal/disk"
 )
@@ -31,20 +30,21 @@ import (
 //
 // passes NOATIME flag for reads on Unix systems to avoid atime updates.
 func ReadFile(name string) ([]byte, error) {
-	f, err := os.OpenFile(name, readMode, 0)
+	f, err := disk.OpenFileDirectIO(name, readMode, 0666)
 	if err != nil {
 		return nil, err
 	}
-	if err := disk.Fadvise(f, disk.FadvSequential); err != nil {
-		return nil, err
+	r := &ODirectReader{
+		File:      f,
+		SmallFile: true,
 	}
-	defer disk.Fadvise(f, disk.FadvNoReuse)
-	defer f.Close()
+	defer r.Close()
+
 	st, err := f.Stat()
 	if err != nil {
-		return io.ReadAll(f)
+		return io.ReadAll(r)
 	}
 	dst := make([]byte, st.Size())
-	_, err = io.ReadFull(f, dst)
+	_, err = io.ReadFull(r, dst)
 	return dst, err
 }