FUSE Mount: Fix buffer allocation during copy (#6863)

Fix buffer allocation during FUSE copy

weed/mount/weedfs_file_copy_range.go

@@ -1,13 +1,13 @@
 package mount
 
 import (
-	"github.com/seaweedfs/seaweedfs/weed/util"
 	"net/http"
 	"time"
 
 	"github.com/hanwen/go-fuse/v2/fuse"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
+	"github.com/seaweedfs/seaweedfs/weed/util"
 )
 
 // CopyFileRange copies data from one file to another from and to specified offsets.
@@ -70,30 +70,85 @@ func (wfs *WFS) CopyFileRange(cancel <-chan struct{}, in *fuse.CopyFileRangeIn)
 		in.OffOut, in.OffOut+in.Len,
 	)
 
-	data := make([]byte, in.Len)
-	totalRead, err := readDataByFileHandle(data, fhIn, int64(in.OffIn))
-	if err != nil {
-		glog.Warningf("file handle read %s %d: %v", fhIn.FullPath(), totalRead, err)
-		return 0, fuse.EIO
+	// Concurrent copy operations could allocate too much memory, so we want to
+	// throttle our concurrency, scaling with the number of writers the mount
+	// was configured with.
+	if wfs.concurrentCopiersSem != nil {
+		wfs.concurrentCopiersSem <- struct{}{}
+		defer func() { <-wfs.concurrentCopiersSem }()
 	}
-	data = data[:totalRead]
 
-	if totalRead == 0 {
+	// We want to stream the copy operation to avoid allocating massive buffers.
+	nowUnixNano := time.Now().UnixNano()
+	totalCopied := int64(0)
+	buff := wfs.copyBufferPool.Get().([]byte)
+	defer wfs.copyBufferPool.Put(buff)
+	for {
+		// Comply with cancellation as best as we can, given that the underlying
+		// IO functions aren't cancellation-aware.
+		select {
+		case <-cancel:
+			glog.Warningf("canceled CopyFileRange for %s (copied %d)",
+				fhIn.FullPath(), totalCopied)
+			return uint32(totalCopied), fuse.EINTR
+		default: // keep going
+		}
+
+		// We can save one IO by breaking early if we already know the next read
+		// will result in zero bytes.
+		remaining := int64(in.Len) - totalCopied
+		readLen := min(remaining, int64(len(buff)))
+		if readLen == 0 {
+			break
+		}
+
+		// Perform the read
+		offsetIn := totalCopied + int64(in.OffIn)
+		numBytesRead, err := readDataByFileHandle(
+			buff[:readLen], fhIn, offsetIn)
+		if err != nil {
+			glog.Warningf("file handle read %s %d (total %d): %v",
+				fhIn.FullPath(), numBytesRead, totalCopied, err)
+			return 0, fuse.EIO
+		}
+
+		// Break if we're done copying (no more bytes to read)
+		if numBytesRead == 0 {
+			break
+		}
+
+		offsetOut := int64(in.OffOut) + totalCopied
+
+		// Detect mime type only during the beginning of our stream, since
+		// DetectContentType is expecting some of the first 512 bytes of the
+		// file. See [http.DetectContentType] for details.
+		if offsetOut <= 512 {
+			fhOut.contentType = http.DetectContentType(buff[:numBytesRead])
+		}
+
+		// Perform the write
+		fhOut.dirtyPages.writerPattern.MonitorWriteAt(offsetOut, int(numBytesRead))
+		fhOut.dirtyPages.AddPage(
+			offsetOut,
+			buff[:numBytesRead],
+			fhOut.dirtyPages.writerPattern.IsSequentialMode(),
+			nowUnixNano)
+
+		// Accumulate for the next loop iteration
+		totalCopied += numBytesRead
+	}
+
+	if totalCopied == 0 {
 		return 0, fuse.OK
 	}
 
-	// put data at the specified offset in target file
-	fhOut.dirtyPages.writerPattern.MonitorWriteAt(int64(in.OffOut), int(in.Len))
+	fhOut.entry.Attributes.FileSize = uint64(max(
+		totalCopied+int64(in.OffOut),
+		int64(fhOut.entry.Attributes.FileSize),
+	))
 	fhOut.entry.Content = nil
-	fhOut.dirtyPages.AddPage(int64(in.OffOut), data, fhOut.dirtyPages.writerPattern.IsSequentialMode(), time.Now().UnixNano())
-	fhOut.entry.Attributes.FileSize = uint64(max(int64(in.OffOut)+totalRead, int64(fhOut.entry.Attributes.FileSize)))
 	fhOut.dirtyMetadata = true
-	written = uint32(totalRead)
-
-	// detect mime type
-	if written > 0 && in.OffOut <= 512 {
-		fhOut.contentType = http.DetectContentType(data)
-	}
 
+	written = uint32(totalCopied)
 	return written, fuse.OK
 }