fix ENOMEM dedup errors

Fixes #1

I can now dedup my whole FS without any error.
This was occuring because linux only allows to pass one page worth of description and this end up at 127 files, if trying to dedup 128+ files together it would error.

Author: Jorropo

Diff for: main.go

@@ -38,6 +38,9 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+const pageSize = 4096 // FIXME: should vary this properly, it's fine to underestimate but not overestimate
+const maxInfos = (pageSize - unix.SizeofRawFileDedupeRange) / unix.SizeofRawFileDedupeRangeInfo
+
 var printLock sync.Mutex
 
 func print(s string) {
@@ -306,6 +309,7 @@ func dedup(backoff chan struct{}, length uint64, paths ...string) {
 	var hasFailed atomic.Bool
 
 	dedups := make([]unix.FileDedupeRangeInfo, len(paths))
+	// FIXME: we don't need that many paths open at once, we could be more economical about fds if we only openned the current batch files.
 	for i, p := range paths {
 		// Use a goroutine instead of recursion and block the callback in case we have an enormous amount of duplicates.
 		go func() {
@@ -369,46 +373,54 @@ func dedup(backoff chan struct{}, length uint64, paths ...string) {
 		return
 	}
 
+	var dedupped uint64
 	source := valid[0].Dest_fd
 	valid = valid[1:]
-	var dedupped, offset uint64
 	for {
-		arg := &unix.FileDedupeRange{
-			Src_length: length,
-			Src_offset: offset,
-			Info:       valid,
-		}
-		err := unix.IoctlFileDedupeRange(int(source), arg)
-		if err != nil {
-			print(paths[0] + ": (FileDedupeRange): " + err.Error())
-			totalDeddupingErrors.Add(uint64(len(valid)))
-			return
-		}
+		current := valid[:min(len(valid), maxInfos)]
+		var offset uint64
+		for {
+			arg := &unix.FileDedupeRange{
+				Src_length: length - offset,
+				Src_offset: offset,
+				Info:       current,
+			}
+			err := unix.IoctlFileDedupeRange(int(source), arg)
+			if err != nil {
+				print(paths[0] + ": (FileDedupeRange): " + err.Error())
+				totalDeddupingErrors.Add(uint64(len(current)))
+				return
+			}
 
-		var best uint64
-		nextValid := valid[:0]
-		for i, v := range valid {
-			bytesDedupped := v.Bytes_deduped
-			dedupped += bytesDedupped
-			if bytesDedupped < best {
-				// this file is having issues, forget about it.
-				continue
+			var best uint64
+			nextCurrent := current[:0]
+			for i, v := range current {
+				bytesDedupped := v.Bytes_deduped
+				dedupped += bytesDedupped
+				if bytesDedupped < best {
+					// this file is having issues, forget about it.
+					continue
+				}
+				if best < bytesDedupped {
+					// previous files were doing poorly, forget about them.
+					best = bytesDedupped
+					nextCurrent = current[i:i]
+				}
+				v.Dest_offset += bytesDedupped
+				nextCurrent = append(nextCurrent, v)
 			}
-			if best < bytesDedupped {
-				// previous files were doing poorly, forget about them.
-				best = bytesDedupped
-				nextValid = valid[i:i]
+			current = nextCurrent
+			offset += best
+
+			if offset == length || best == 0 {
+				break
 			}
-			v.Dest_offset += bytesDedupped
-			nextValid = append(nextValid, v)
 		}
-		valid = nextValid
-		offset += best
-		length -= best
 
-		if length == 0 || best == 0 {
+		if len(valid) <= maxInfos {
 			break
 		}
+		valid = valid[maxInfos:]
 	}
 	totalDedupped.Add(dedupped)
 }