btrfsitem: Add `Free` and `CloneItem` methods to Items

29 files changed, 539 insertions, 82 deletions

diff --git a/lib/btrfs/Makefile b/lib/btrfs/Makefile
index ac39425..a1fe747 100644
--- a/lib/btrfs/Makefile
+++ b/lib/btrfs/Makefile
@@ -8,9 +8,9 @@
 
 btrfsitem/items.txt: btrfsitem $(wildcard btrfsitem/item_*.go) $(MAKEFILE_LIST)
 	{ \
-	  sed -En 's,^type (\S+) .* // (.*=.*),\1 \2,p' $(filter btrfsitem/item_%.go,$^) | while read -r typ keys; do \
+	  sed -En 's,^type (\S+) .* // (trivial|complex) (.*=.*),\1 \2 \3,p' $(filter btrfsitem/item_%.go,$^) | while read -r typ class keys; do \
 	    for key in $$keys; do \
-	      echo "$$key" "$$typ"; \
+	      echo "$$key" "$$class" "$$typ"; \
 	    done; \
 	  done; \
 	} | LC_COLLATE=C sort >$@
@@ -24,27 +24,47 @@ btrfsitem/items_gen.go: btrfsitem/items.txt $(MAKEFILE_LIST)
 	  echo 'import ('; \
 	  echo   '"reflect"'; \
 	  echo; \
+	  echo   '"git.lukeshu.com/go/typedsync"'; \
+	  echo; \
 	  echo   '"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"'; \
 	  echo ')'; \
 	  echo 'const ('; \
-	  sed -E 's/(.*)=(.*) (.*)/\1_KEY=btrfsprim.\1_KEY/' $<; \
+	  sed -E 's/(.*)=(.*) (trivial|complex) (.*)/\1_KEY=btrfsprim.\1_KEY/' $<; \
 	  echo ')'; \
 	  echo 'var ('; \
-	  sed -E 's/(.*)=(.*) (.*)/\3/p' $< | LC_COLLATE=C sort -u | sed 's/.*/\l&Type = reflect.TypeOf(&{})/'; \
+	  sed -E 's/(.*)=(.*) (trivial|complex) (.*)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/\l&Type = reflect.TypeOf(&{})/'; \
 	  echo ')'; \
 	  echo '// keytype2gotype is used by UnmarshalItem.'; \
 	  echo 'var keytype2gotype = map[Type]reflect.Type{'; \
-	  sed -En 's/(.*)=([^:]*) (.*)/\1_KEY: \l\3Type,/p' $<; \
+	  sed -En 's/(.*)=([^:]*) (trivial|complex) (.*)/\1_KEY: \l\4Type,/p' $<; \
 	  echo '}'; \
 	  echo '// untypedObjID2gotype is used by UnmarshalItem.'; \
 	  echo 'var untypedObjID2gotype = map[btrfsprim.ObjID]reflect.Type{'; \
-	  sed -En 's/UNTYPED=0:(.*) (.*)/btrfsprim.\1: \l\2Type,/p' $<; \
+	  sed -En 's/UNTYPED=0:(.*) (trivial|complex) (.*)/btrfsprim.\1: \l\3Type,/p' $<; \
+	  echo '}'; \
+	  echo '// Pools.'; \
+	  echo 'var ('; \
+	  sed -E 's/(.*)=(.*) (trivial|complex) (.*)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/\l&Pool = typedsync.Pool[Item]{New: func() Item { return new(&) }}/'; \
+	  echo ')'; \
+	  echo '// gotype2pool is used by UnmarshalItem.'; \
+	  echo 'var gotype2pool = map[reflect.Type]*typedsync.Pool[Item]{'; \
+	  sed -E 's/(.*)=(.*) (trivial|complex) (.*)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/\l&Type: \&\l&Pool,/'; \
 	  echo '}'; \
 	  echo '// isItem implements Item.'; \
-	  sed -En 's/(.*)=(.*) (.+)/\3/p' $< | LC_COLLATE=C sort -u | sed 's/.*/func (*&) isItem() {}/'; \
-	  echo '// Type assertions.'; \
+	  sed -En 's/(.*)=(.*) (trivial|complex) (.+)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/func (*&) isItem() {}/'; \
+	  echo '// Free implements Item.'; \
+	  sed -En 's/(.*)=(.*) (trivial) (.+)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/func (o *&) Free() {*o = &{}; \l&Pool.Put(o)}/'; \
+	  echo '// Clone is a handy method.'; \
+	  sed -En 's/(.*)=(.*) (trivial) (.+)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/func (o &) Clone() & { return o }/'; \
+	  echo '// CloneItem implements Item.'; \
+	  sed -En 's/(.*)=(.*) (trivial|complex) (.+)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/func (o *&) CloneItem() Item { ret, _ := \l&Pool.Get(); *(ret.(*&)) = o.Clone(); return ret }/'; \
+	  echo '// Item type assertions.'; \
+	  echo 'var ('; \
+	  sed -En 's/(.*)=(.*) (trivial|complex) (.+)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/_ Item = (*&)(nil)/'; \
+	  echo ')'; \
+	  echo '// Clone type assertions.'; \
 	  echo 'var ('; \
-	  sed -En 's/(.*)=(.*) (.+)/\3/p' $< | LC_COLLATE=C sort -u | sed 's/.*/_ Item = (*&)(nil)/'; \
+	  sed -En 's/(.*)=(.*) (trivial|complex) (.+)/\4/p' $< | LC_COLLATE=C sort -u | sed 's/.*/_ interface{ Clone() & } = &{}/'; \
 	  echo ')'; \
 	} | sed 's/uUID/uuid/g' | gofmt >$@
 files += btrfsitem/items_gen.go
@@ -57,11 +77,11 @@ btrfsprim/itemtype.go: btrfsitem/items.txt $(MAKEFILE_LIST)
 	  echo 'import "fmt"'; \
 	  echo 'type ItemType uint8'; \
 	  echo 'const ('; \
-	  sed -E 's,(.*)=([^:]*)(:.*)? (.*),\1_KEY=ItemType(\2),' $< | uniq; \
+	  sed -E 's,(.*)=([^:]*)(:.*)? (trivial|complex) (.*),\1_KEY=ItemType(\2),' $< | uniq; \
 	  echo ')'; \
 	  echo 'func (t ItemType) String() string {'; \
 	  echo '  names := map[ItemType]string{'; \
-	  sed -E 's@(.*)=(.*) (.*)@\1_KEY: "\1",@' $< | sed 's/"UUID_/&KEY_/'; \
+	  sed -E 's@(.*)=(.*) (trivial|complex) (.*)@\1_KEY: "\1",@' $< | sed 's/"UUID_/&KEY_/'; \
 	  echo '  }'; \
 	  echo '  if name, ok := names[t]; ok {'; \
 	  echo '    return name'; \
diff --git a/lib/btrfs/btrfsitem/item_blockgroup.go b/lib/btrfs/btrfsitem/item_blockgroup.go
index 6fc09ac..ae0ca12 100644
--- a/lib/btrfs/btrfsitem/item_blockgroup.go
+++ b/lib/btrfs/btrfsitem/item_blockgroup.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -12,7 +12,7 @@ import (
 
 // key.objectid = logical_addr
 // key.offset = size of chunk
-type BlockGroup struct { // BLOCK_GROUP_ITEM=192
+type BlockGroup struct { // trivial BLOCK_GROUP_ITEM=192
 	Used          int64                    `bin:"off=0, siz=8"`
 	ChunkObjectID btrfsprim.ObjID          `bin:"off=8, siz=8"` // always FIRST_CHUNK_TREE_OBJECTID
 	Flags         btrfsvol.BlockGroupFlags `bin:"off=16, siz=8"`
diff --git a/lib/btrfs/btrfsitem/item_chunk.go b/lib/btrfs/btrfsitem/item_chunk.go
index e0776ad..2280a0b 100644
--- a/lib/btrfs/btrfsitem/item_chunk.go
+++ b/lib/btrfs/btrfsitem/item_chunk.go
@@ -15,7 +15,7 @@ import (
 //
 // key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID
 // key.offset = logical_addr
-type Chunk struct { // CHUNK_ITEM=228
+type Chunk struct { // complex CHUNK_ITEM=228
 	Head    ChunkHeader
 	Stripes []ChunkStripe
 }
@@ -60,20 +60,36 @@ func (chunk Chunk) Mappings(key btrfsprim.Key) []btrfsvol.Mapping {
 	return ret
 }
 
+var chunkStripePool containers.SlicePool[ChunkStripe]
+
+func (chunk *Chunk) Free() {
+	for i := range chunk.Stripes {
+		chunk.Stripes[i] = ChunkStripe{}
+	}
+	chunkStripePool.Put(chunk.Stripes)
+	*chunk = Chunk{}
+	chunkPool.Put(chunk)
+}
+
+func (chunk Chunk) Clone() Chunk {
+	ret := chunk
+	ret.Stripes = chunkStripePool.Get(len(chunk.Stripes))
+	copy(ret.Stripes, chunk.Stripes)
+	return ret
+}
+
 func (chunk *Chunk) UnmarshalBinary(dat []byte) (int, error) {
 	n, err := binstruct.Unmarshal(dat, &chunk.Head)
 	if err != nil {
 		return n, err
 	}
-	chunk.Stripes = make([]ChunkStripe, 0, chunk.Head.NumStripes)
-	for i := 0; i < int(chunk.Head.NumStripes); i++ {
-		var stripe ChunkStripe
-		_n, err := binstruct.Unmarshal(dat[n:], &stripe)
+	chunk.Stripes = chunkStripePool.Get(int(chunk.Head.NumStripes))
+	for i := range chunk.Stripes {
+		_n, err := binstruct.Unmarshal(dat[n:], &chunk.Stripes[i])
 		n += _n
 		if err != nil {
 			return n, err
 		}
-		chunk.Stripes = append(chunk.Stripes, stripe)
 	}
 	return n, nil
 }
diff --git a/lib/btrfs/btrfsitem/item_dev.go b/lib/btrfs/btrfsitem/item_dev.go
index fd7f458..188711e 100644
--- a/lib/btrfs/btrfsitem/item_dev.go
+++ b/lib/btrfs/btrfsitem/item_dev.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -12,7 +12,7 @@ import (
 
 // key.objectid = BTRFS_DEV_ITEMS_OBJECTID
 // key.offset = device_id (starting at 1)
-type Dev struct { // DEV_ITEM=216
+type Dev struct { // trivial DEV_ITEM=216
 	DevID btrfsvol.DeviceID `bin:"off=0x0,    siz=0x8"`
 
 	NumBytes     uint64 `bin:"off=0x8,    siz=0x8"`
diff --git a/lib/btrfs/btrfsitem/item_devextent.go b/lib/btrfs/btrfsitem/item_devextent.go
index 47bdbcf..cade165 100644
--- a/lib/btrfs/btrfsitem/item_devextent.go
+++ b/lib/btrfs/btrfsitem/item_devextent.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -12,7 +12,7 @@ import (
 
 // key.objectid = device_id
 // key.offset = physical_addr
-type DevExtent struct { // DEV_EXTENT=204
+type DevExtent struct { // trivial DEV_EXTENT=204
 	ChunkTree     btrfsprim.ObjID      `bin:"off=0, siz=8"`  // always CHUNK_TREE_OBJECTID
 	ChunkObjectID btrfsprim.ObjID      `bin:"off=8, siz=8"`  // which chunk within .ChunkTree owns this extent, always FIRST_CHUNK_TREE_OBJECTID
 	ChunkOffset   btrfsvol.LogicalAddr `bin:"off=16, siz=8"` // offset of the CHUNK_ITEM that owns this extent, within the .ChunkObjectID
diff --git a/lib/btrfs/btrfsitem/item_dir.go b/lib/btrfs/btrfsitem/item_dir.go
index 584e44d..0049072 100644
--- a/lib/btrfs/btrfsitem/item_dir.go
+++ b/lib/btrfs/btrfsitem/item_dir.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -23,7 +23,7 @@ func NameHash(dat []byte) uint64 {
 // key.offset =
 //   - for DIR_ITEM and XATTR_ITEM = NameHash(name)
 //   - for DIR_INDEX               = index id in the directory (starting at 2, because "." and "..")
-type DirEntry struct { // DIR_ITEM=84 DIR_INDEX=96 XATTR_ITEM=24
+type DirEntry struct { // complex DIR_ITEM=84 DIR_INDEX=96 XATTR_ITEM=24
 	Location      btrfsprim.Key `bin:"off=0x0, siz=0x11"`
 	TransID       int64         `bin:"off=0x11, siz=8"`
 	DataLen       uint16        `bin:"off=0x19, siz=2"` // [ignored-when-writing]
@@ -34,6 +34,19 @@ type DirEntry struct { // DIR_ITEM=84 DIR_INDEX=96 XATTR_ITEM=24
 	Name          []byte `bin:"-"`
 }
 
+func (o *DirEntry) Free() {
+	bytePool.Put(o.Data)
+	bytePool.Put(o.Name)
+	*o = DirEntry{}
+	dirEntryPool.Put(o)
+}
+
+func (o DirEntry) Clone() DirEntry {
+	o.Data = cloneBytes(o.Data)
+	o.Name = cloneBytes(o.Name)
+	return o
+}
+
 func (o *DirEntry) UnmarshalBinary(dat []byte) (int, error) {
 	if err := binutil.NeedNBytes(dat, 0x1e); err != nil {
 		return 0, err
@@ -49,9 +62,9 @@ func (o *DirEntry) UnmarshalBinary(dat []byte) (int, error) {
 	if err := binutil.NeedNBytes(dat, 0x1e+int(o.DataLen)+int(o.NameLen)); err != nil {
 		return 0, err
 	}
-	o.Name = dat[n : n+int(o.NameLen)]
+	o.Name = cloneBytes(dat[n : n+int(o.NameLen)])
 	n += int(o.NameLen)
-	o.Data = dat[n : n+int(o.DataLen)]
+	o.Data = cloneBytes(dat[n : n+int(o.DataLen)])
 	n += int(o.DataLen)
 	return n, nil
 }
diff --git a/lib/btrfs/btrfsitem/item_empty.go b/lib/btrfs/btrfsitem/item_empty.go
index 47b4a15..7343c8f 100644
--- a/lib/btrfs/btrfsitem/item_empty.go
+++ b/lib/btrfs/btrfsitem/item_empty.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -8,6 +8,6 @@ import (
 	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct"
 )
 
-type Empty struct { // ORPHAN_ITEM=48 TREE_BLOCK_REF=176 SHARED_BLOCK_REF=182 FREE_SPACE_EXTENT=199 QGROUP_RELATION=246
+type Empty struct { // trivial ORPHAN_ITEM=48 TREE_BLOCK_REF=176 SHARED_BLOCK_REF=182 FREE_SPACE_EXTENT=199 QGROUP_RELATION=246
 	binstruct.End `bin:"off=0"`
 }
diff --git a/lib/btrfs/btrfsitem/item_extent.go b/lib/btrfs/btrfsitem/item_extent.go
index 72371a9..3789cfe 100644
--- a/lib/btrfs/btrfsitem/item_extent.go
+++ b/lib/btrfs/btrfsitem/item_extent.go
@@ -9,18 +9,44 @@ import (
 
 	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct"
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
+	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
 	"git.lukeshu.com/btrfs-progs-ng/lib/fmtutil"
 )
 
 // key.objectid = laddr of the extent
 // key.offset = length of the extent
-type Extent struct { // EXTENT_ITEM=168
+type Extent struct { // complex EXTENT_ITEM=168
 	Head ExtentHeader
 	Info TreeBlockInfo // only if .Head.Flags.Has(EXTENT_FLAG_TREE_BLOCK)
 	Refs []ExtentInlineRef
 }
 
+var extentInlineRefPool containers.SlicePool[ExtentInlineRef]
+
+func (o *Extent) Free() {
+	for i := range o.Refs {
+		if o.Refs[i].Body != nil {
+			o.Refs[i].Body.Free()
+		}
+		o.Refs[i] = ExtentInlineRef{}
+	}
+	extentInlineRefPool.Put(o.Refs)
+	*o = Extent{}
+	extentPool.Put(o)
+}
+
+func (o Extent) Clone() Extent {
+	ret := o
+	ret.Refs = extentInlineRefPool.Get(len(o.Refs))
+	copy(ret.Refs, o.Refs)
+	for i := range ret.Refs {
+		ret.Refs[i].Body = o.Refs[i].Body.CloneItem()
+	}
+	return ret
+}
+
 func (o *Extent) UnmarshalBinary(dat []byte) (int, error) {
+	*o = Extent{}
 	n, err := binstruct.Unmarshal(dat, &o.Head)
 	if err != nil {
 		return n, err
@@ -32,7 +58,9 @@ func (o *Extent) UnmarshalBinary(dat []byte) (int, error) {
 			return n, err
 		}
 	}
-	o.Refs = nil
+	if n < len(dat) {
+		o.Refs = extentInlineRefPool.Get(1)[:0]
+	}
 	for n < len(dat) {
 		var ref ExtentInlineRef
 		_n, err := binstruct.Unmarshal(dat[n:], &ref)
@@ -114,7 +142,7 @@ func (o *ExtentInlineRef) UnmarshalBinary(dat []byte) (int, error) {
 			return n, err
 		}
 	case EXTENT_DATA_REF_KEY:
-		dref := new(ExtentDataRef)
+		dref, _ := extentDataRefPool.Get()
 		_n, err := binstruct.Unmarshal(dat[n:], dref)
 		n += _n
 		o.Body = dref
@@ -127,7 +155,7 @@ func (o *ExtentInlineRef) UnmarshalBinary(dat []byte) (int, error) {
 		if err != nil {
 			return n, err
 		}
-		sref := new(SharedDataRef)
+		sref, _ := sharedDataRefPool.Get()
 		_n, err = binstruct.Unmarshal(dat[n:], sref)
 		n += _n
 		o.Body = sref
diff --git a/lib/btrfs/btrfsitem/item_extentcsum.go b/lib/btrfs/btrfsitem/item_extentcsum.go
index bcfe334..dfa166d 100644
--- a/lib/btrfs/btrfsitem/item_extentcsum.go
+++ b/lib/btrfs/btrfsitem/item_extentcsum.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -13,7 +13,7 @@ import (
 
 // key.objectid = BTRFS_EXTENT_CSUM_OBJECTID
 // key.offset = laddr of checksummed region
-type ExtentCSum struct { // EXTENT_CSUM=128
+type ExtentCSum struct { // trivial EXTENT_CSUM=128
 	// Checksum of each sector starting at key.offset
 	btrfssum.SumRun[btrfsvol.LogicalAddr]
 }
diff --git a/lib/btrfs/btrfsitem/item_extentdataref.go b/lib/btrfs/btrfsitem/item_extentdataref.go
index 8c856e2..6f2257b 100644
--- a/lib/btrfs/btrfsitem/item_extentdataref.go
+++ b/lib/btrfs/btrfsitem/item_extentdataref.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -11,7 +11,7 @@ import (
 
 // key.objectid = laddr of the extent being referenced
 // key.offset = crc32c([root,objectid,offset])
-type ExtentDataRef struct { // EXTENT_DATA_REF=178
+type ExtentDataRef struct { // trivial EXTENT_DATA_REF=178
 	Root          btrfsprim.ObjID `bin:"off=0, siz=8"`  // subvolume tree ID that references this extent
 	ObjectID      btrfsprim.ObjID `bin:"off=8, siz=8"`  // inode number that references this extent within the .Root subvolume
 	Offset        int64           `bin:"off=16, siz=8"` // byte offset for the extent within the file
diff --git a/lib/btrfs/btrfsitem/item_fileextent.go b/lib/btrfs/btrfsitem/item_fileextent.go
index 83e5d34..30a14ef 100644
--- a/lib/btrfs/btrfsitem/item_fileextent.go
+++ b/lib/btrfs/btrfsitem/item_fileextent.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -14,7 +14,7 @@ import (
 
 // key.objectid = inode
 // key.offset = offset within file
-type FileExtent struct { // EXTENT_DATA=108
+type FileExtent struct { // complex EXTENT_DATA=108
 	Generation btrfsprim.Generation `bin:"off=0x0, siz=0x8"` // transaction ID that created this extent
 	RAMBytes   int64                `bin:"off=0x8, siz=0x8"` // upper bound of what compressed data will decompress to
 
@@ -46,6 +46,17 @@ type FileExtentExtent struct {
 	binstruct.End `bin:"off=0x20"`
 }
 
+func (o *FileExtent) Free() {
+	bytePool.Put(o.BodyInline)
+	*o = FileExtent{}
+	fileExtentPool.Put(o)
+}
+
+func (o FileExtent) Clone() FileExtent {
+	o.BodyInline = cloneBytes(o.BodyInline)
+	return o
+}
+
 func (o *FileExtent) UnmarshalBinary(dat []byte) (int, error) {
 	n, err := binstruct.UnmarshalWithoutInterface(dat, o)
 	if err != nil {
@@ -53,7 +64,7 @@ func (o *FileExtent) UnmarshalBinary(dat []byte) (int, error) {
 	}
 	switch o.Type {
 	case FILE_EXTENT_INLINE:
-		o.BodyInline = dat[n:]
+		o.BodyInline = cloneBytes(dat[n:])
 		n += len(o.BodyInline)
 	case FILE_EXTENT_REG, FILE_EXTENT_PREALLOC:
 		_n, err := binstruct.Unmarshal(dat[n:], &o.BodyExtent)
diff --git a/lib/btrfs/btrfsitem/item_freespacebitmap.go b/lib/btrfs/btrfsitem/item_freespacebitmap.go
index 742d126..ebc00e4 100644
--- a/lib/btrfs/btrfsitem/item_freespacebitmap.go
+++ b/lib/btrfs/btrfsitem/item_freespacebitmap.go
@@ -6,15 +6,26 @@ package btrfsitem
 
 // key.objectid = object ID of the FreeSpaceInfo (logical_addr)
 // key.offset = offset of the FreeSpaceInfo (size)
-type FreeSpaceBitmap struct { // FREE_SPACE_BITMAP=200
+type FreeSpaceBitmap struct { // complex FREE_SPACE_BITMAP=200
 	Bitmap []byte
 }
 
+func (o *FreeSpaceBitmap) Free() {
+	bytePool.Put(o.Bitmap)
+	*o = FreeSpaceBitmap{}
+	freeSpaceBitmapPool.Put(o)
+}
+
+func (o FreeSpaceBitmap) Clone() FreeSpaceBitmap {
+	o.Bitmap = cloneBytes(o.Bitmap)
+	return o
+}
+
 func (o *FreeSpaceBitmap) UnmarshalBinary(dat []byte) (int, error) {
-	o.Bitmap = dat
+	o.Bitmap = cloneBytes(dat)
 	return len(dat), nil
 }
 
 func (o FreeSpaceBitmap) MarshalBinary() ([]byte, error) {
-	return o.Bitmap, nil
+	return append([]byte(nil), o.Bitmap...), nil
 }
diff --git a/lib/btrfs/btrfsitem/item_freespaceinfo.go b/lib/btrfs/btrfsitem/item_freespaceinfo.go
index b38da20..0699367 100644
--- a/lib/btrfs/btrfsitem/item_freespaceinfo.go
+++ b/lib/btrfs/btrfsitem/item_freespaceinfo.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -11,7 +11,7 @@ import (
 
 // key.objectid = object ID of the BlockGroup (logical_addr)
 // key.offset = offset of the BlockGroup (size)
-type FreeSpaceInfo struct { // FREE_SPACE_INFO=198
+type FreeSpaceInfo struct { // trivial FREE_SPACE_INFO=198
 	ExtentCount   int32          `bin:"off=0, siz=4"`
 	Flags         FreeSpaceFlags `bin:"off=4, siz=4"`
 	binstruct.End `bin:"off=8"`
diff --git a/lib/btrfs/btrfsitem/item_inode.go b/lib/btrfs/btrfsitem/item_inode.go
index 704b56a..69f8445 100644
--- a/lib/btrfs/btrfsitem/item_inode.go
+++ b/lib/btrfs/btrfsitem/item_inode.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -12,7 +12,7 @@ import (
 
 // key.objectid = inode number
 // key.offset = 0
-type Inode struct { // INODE_ITEM=1
+type Inode struct { // trivial INODE_ITEM=1
 	Generation    btrfsprim.Generation `bin:"off=0x00, siz=0x08"`
 	TransID       int64                `bin:"off=0x08, siz=0x08"`
 	Size          int64                `bin:"off=0x10, siz=0x08"` // stat
diff --git a/lib/btrfs/btrfsitem/item_inoderef.go b/lib/btrfs/btrfsitem/item_inoderef.go
index c90fe44..074b26d 100644
--- a/lib/btrfs/btrfsitem/item_inoderef.go
+++ b/lib/btrfs/btrfsitem/item_inoderef.go
@@ -9,6 +9,7 @@ import (
 
 	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct"
 	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct/binutil"
+	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
 )
 
 // key.objectid = inode number of the file
@@ -16,12 +17,37 @@ import (
 //
 // Might have multiple entries if the same file has multiple hardlinks
 // in the same directory.
-type InodeRefs struct { // INODE_REF=12
+type InodeRefs struct { // complex INODE_REF=12
 	Refs []InodeRef
 }
 
+var inodeRefPool containers.SlicePool[InodeRef]
+
+func (o *InodeRefs) Free() {
+	for i := range o.Refs {
+		bytePool.Put(o.Refs[i].Name)
+		o.Refs[i] = InodeRef{}
+	}
+	inodeRefPool.Put(o.Refs)
+	*o = InodeRefs{}
+	inodeRefsPool.Put(o)
+}
+
+func (o InodeRefs) Clone() InodeRefs {
+	var ret InodeRefs
+	ret.Refs = inodeRefPool.Get(len(o.Refs))
+	copy(ret.Refs, o.Refs)
+	for i := range ret.Refs {
+		ret.Refs[i].Name = cloneBytes(o.Refs[i].Name)
+	}
+	return ret
+}
+
 func (o *InodeRefs) UnmarshalBinary(dat []byte) (int, error) {
 	o.Refs = nil
+	if len(dat) > 0 {
+		o.Refs = inodeRefPool.Get(1)[:0]
+	}
 	n := 0
 	for n < len(dat) {
 		var ref InodeRef
@@ -70,7 +96,7 @@ func (o *InodeRef) UnmarshalBinary(dat []byte) (int, error) {
 		return 0, err
 	}
 	dat = dat[n:]
-	o.Name = dat[:o.NameLen]
+	o.Name = cloneBytes(dat[:o.NameLen])
 	n += int(o.NameLen)
 	return n, nil
 }
diff --git a/lib/btrfs/btrfsitem/item_metadata.go b/lib/btrfs/btrfsitem/item_metadata.go
index e90af8d..db2315e 100644
--- a/lib/btrfs/btrfsitem/item_metadata.go
+++ b/lib/btrfs/btrfsitem/item_metadata.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -9,17 +9,42 @@ import (
 )
 
 // Metadata is like Extent, but doesn't have .Info.
-type Metadata struct { // METADATA_ITEM=169
+type Metadata struct { // complex METADATA_ITEM=169
 	Head ExtentHeader
 	Refs []ExtentInlineRef
 }
 
+func (o *Metadata) Free() {
+	for i := range o.Refs {
+		if o.Refs[i].Body != nil {
+			o.Refs[i].Body.Free()
+		}
+		o.Refs[i] = ExtentInlineRef{}
+	}
+	extentInlineRefPool.Put(o.Refs)
+	*o = Metadata{}
+	metadataPool.Put(o)
+}
+
+func (o Metadata) Clone() Metadata {
+	ret := o
+	ret.Refs = extentInlineRefPool.Get(len(o.Refs))
+	copy(ret.Refs, o.Refs)
+	for i := range ret.Refs {
+		ret.Refs[i].Body = o.Refs[i].Body.CloneItem()
+	}
+	return ret
+}
+
 func (o *Metadata) UnmarshalBinary(dat []byte) (int, error) {
+	*o = Metadata{}
 	n, err := binstruct.Unmarshal(dat, &o.Head)
 	if err != nil {
 		return n, err
 	}
-	o.Refs = nil
+	if n < len(dat) {
+		o.Refs = extentInlineRefPool.Get(1)[:0]
+	}
 	for n < len(dat) {
 		var ref ExtentInlineRef
 		_n, err := binstruct.Unmarshal(dat[n:], &ref)
diff --git a/lib/btrfs/btrfsitem/item_persistent.go b/lib/btrfs/btrfsitem/item_persistent.go
index a827074..4655aee 100644
--- a/lib/btrfs/btrfsitem/item_persistent.go
+++ b/lib/btrfs/btrfsitem/item_persistent.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -17,7 +17,7 @@ const (
 	DEV_STAT_VALUES_MAX
 )
 
-type DevStats struct { // PERSISTENT_ITEM=249
+type DevStats struct { // trivial PERSISTENT_ITEM=249
 	Values        [DEV_STAT_VALUES_MAX]int64 `bin:"off=0, siz=40"`
 	binstruct.End `bin:"off=40"`
 }
diff --git a/lib/btrfs/btrfsitem/item_qgroupinfo.go b/lib/btrfs/btrfsitem/item_qgroupinfo.go
index 8cceb0b..6699030 100644
--- a/lib/btrfs/btrfsitem/item_qgroupinfo.go
+++ b/lib/btrfs/btrfsitem/item_qgroupinfo.go
@@ -11,7 +11,7 @@ import (
 
 // key.objectid = 0
 // key.offset = ID of the qgroup
-type QGroupInfo struct { // QGROUP_INFO=242
+type QGroupInfo struct { // trivial QGROUP_INFO=242
 	Generation                btrfsprim.Generation `bin:"off=0, siz=8"`
 	ReferencedBytes           uint64               `bin:"off=8, siz=8"`
 	ReferencedBytesCompressed uint64               `bin:"off=16, siz=8"`
diff --git a/lib/btrfs/btrfsitem/item_qgrouplimit.go b/lib/btrfs/btrfsitem/item_qgrouplimit.go
index 9d1e05f..47f7eca 100644
--- a/lib/btrfs/btrfsitem/item_qgrouplimit.go
+++ b/lib/btrfs/btrfsitem/item_qgrouplimit.go
@@ -36,7 +36,7 @@ func (f QGroupLimitFlags) String() string {
 
 // key.objectid = 0
 // key.offset = ID of the qgroup
-type QGroupLimit struct { // QGROUP_LIMIT=244
+type QGroupLimit struct { // trivial QGROUP_LIMIT=244
 	Flags         QGroupLimitFlags `bin:"off=0, siz=8"`
 	MaxReferenced uint64           `bin:"off=8, siz=8"`
 	MaxExclusive  uint64           `bin:"off=16, siz=8"`
diff --git a/lib/btrfs/btrfsitem/item_qgroupstatus.go b/lib/btrfs/btrfsitem/item_qgroupstatus.go
index e7bd62c..346c913 100644
--- a/lib/btrfs/btrfsitem/item_qgroupstatus.go
+++ b/lib/btrfs/btrfsitem/item_qgroupstatus.go
@@ -34,7 +34,7 @@ const QGroupStatusVersion uint64 = 1
 
 // key.objectid = 0
 // key.offset = 0
-type QGroupStatus struct { // QGROUP_STATUS=240
+type QGroupStatus struct { // trivial QGROUP_STATUS=240
 	Version        uint64               `bin:"off=0, siz=8"`
 	Generation     btrfsprim.Generation `bin:"off=8, siz=8"`
 	Flags          QGroupStatusFlags    `bin:"off=16, siz=8"`
diff --git a/lib/btrfs/btrfsitem/item_root.go b/lib/btrfs/btrfsitem/item_root.go
index ffbbf4d..c0db900 100644
--- a/lib/btrfs/btrfsitem/item_root.go
+++ b/lib/btrfs/btrfsitem/item_root.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -15,7 +15,7 @@ import (
 // key.offset = either
 //   - 0 if objectid is one of the BTRFS_*_TREE_OBJECTID defines or a non-snapshot volume; or
 //   - transaction_id of when this snapshot was created
-type Root struct { // ROOT_ITEM=132
+type Root struct { // trivial ROOT_ITEM=132
 	Inode         Inode                `bin:"off=0x000, siz=0xa0"` // ???
 	Generation    btrfsprim.Generation `bin:"off=0x0a0, siz=0x08"`
 	RootDirID     btrfsprim.ObjID      `bin:"off=0x0a8, siz=0x08"` // inode number of the root inode
diff --git a/lib/btrfs/btrfsitem/item_rootref.go b/lib/btrfs/btrfsitem/item_rootref.go
index b33883d..4179890 100644
--- a/lib/btrfs/btrfsitem/item_rootref.go
+++ b/lib/btrfs/btrfsitem/item_rootref.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -19,7 +19,7 @@ import (
 //	               ROOT_REF                   | ROOT_BACKREF
 //	key.objectid = ID of the parent subvolume | ID of the child subvolume
 //	key.offset   = ID of the child subvolume  | ID of the parent subvolume
-type RootRef struct { // ROOT_REF=156 ROOT_BACKREF=144
+type RootRef struct { // complex ROOT_REF=156 ROOT_BACKREF=144
 	DirID         btrfsprim.ObjID `bin:"off=0x00, siz=0x8"` // inode of the parent directory of the dir entry
 	Sequence      int64           `bin:"off=0x08, siz=0x8"` // index of that dir entry within the parent
 	NameLen       uint16          `bin:"off=0x10, siz=0x2"` // [ignored-when-writing]
@@ -27,6 +27,17 @@ type RootRef struct { // ROOT_REF=156 ROOT_BACKREF=144
 	Name          []byte `bin:"-"`
 }
 
+func (o *RootRef) Free() {
+	bytePool.Put(o.Name)
+	*o = RootRef{}
+	rootRefPool.Put(o)
+}
+
+func (o RootRef) Clone() RootRef {
+	o.Name = cloneBytes(o.Name)
+	return o
+}
+
 func (o *RootRef) UnmarshalBinary(dat []byte) (int, error) {
 	if err := binutil.NeedNBytes(dat, 0x12); err != nil {
 		return 0, err
@@ -42,7 +53,7 @@ func (o *RootRef) UnmarshalBinary(dat []byte) (int, error) {
 	if err := binutil.NeedNBytes(dat, 0x12+int(o.NameLen)); err != nil {
 		return 0, err
 	}
-	o.Name = dat[n : n+int(o.NameLen)]
+	o.Name = cloneBytes(dat[n : n+int(o.NameLen)])
 	n += int(o.NameLen)
 	return n, nil
 }
diff --git a/lib/btrfs/btrfsitem/item_shareddataref.go b/lib/btrfs/btrfsitem/item_shareddataref.go
index d7765af..6143a5c 100644
--- a/lib/btrfs/btrfsitem/item_shareddataref.go
+++ b/lib/btrfs/btrfsitem/item_shareddataref.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -12,7 +12,7 @@ import (
 //
 // key.offset = laddr of the leaf node containing the FileExtent
 // (EXTENT_DATA_KEY) for this reference.
-type SharedDataRef struct { // SHARED_DATA_REF=184
+type SharedDataRef struct { // trivial SHARED_DATA_REF=184
 	Count         int32 `bin:"off=0, siz=4"` // reference count
 	binstruct.End `bin:"off=4"`
 }
diff --git a/lib/btrfs/btrfsitem/item_untyped.go b/lib/btrfs/btrfsitem/item_untyped.go
index acf4ebe..9bda094 100644
--- a/lib/btrfs/btrfsitem/item_untyped.go
+++ b/lib/btrfs/btrfsitem/item_untyped.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -9,7 +9,7 @@ import (
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
 )
 
-type FreeSpaceHeader struct { // UNTYPED=0:FREE_SPACE_OBJECTID
+type FreeSpaceHeader struct { // trivial UNTYPED=0:FREE_SPACE_OBJECTID
 	Location      btrfsprim.Key        `bin:"off=0x00, siz=0x11"`
 	Generation    btrfsprim.Generation `bin:"off=0x11, siz=0x8"`
 	NumEntries    int64                `bin:"off=0x19, siz=0x8"`
diff --git a/lib/btrfs/btrfsitem/item_uuid.go b/lib/btrfs/btrfsitem/item_uuid.go
index 5f5f357..fca409d 100644
--- a/lib/btrfs/btrfsitem/item_uuid.go
+++ b/lib/btrfs/btrfsitem/item_uuid.go
@@ -16,7 +16,7 @@ import (
 //
 // key.objectid = first half of UUID
 // key.offset = second half of UUID
-type UUIDMap struct { // UUID_SUBVOL=251 UUID_RECEIVED_SUBVOL=252
+type UUIDMap struct { // trivial UUID_SUBVOL=251 UUID_RECEIVED_SUBVOL=252
 	ObjID         btrfsprim.ObjID `bin:"off=0, siz=8"`
 	binstruct.End `bin:"off=8"`
 }
diff --git a/lib/btrfs/btrfsitem/items.go b/lib/btrfs/btrfsitem/items.go
index 9964e2d..49d421f 100644
--- a/lib/btrfs/btrfsitem/items.go
+++ b/lib/btrfs/btrfsitem/items.go
@@ -8,16 +8,21 @@ import (
 	"fmt"
 	"reflect"
 
+	"git.lukeshu.com/go/typedsync"
+
 	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct"
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfssum"
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
+	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
 )
 
 type Type = btrfsprim.ItemType
 
 type Item interface {
 	isItem()
+	Free()
+	CloneItem() Item
 }
 
 type Error struct {
@@ -25,8 +30,23 @@ type Error struct {
 	Err error
 }
 
+var errorPool = &typedsync.Pool[*Error]{New: func() *Error { return new(Error) }}
+
 func (*Error) isItem() {}
 
+func (o *Error) Free() {
+	*o = Error{}
+	errorPool.Put(o)
+}
+
+func (o Error) Clone() Error { return o }
+
+func (o *Error) CloneItem() Item {
+	ret, _ := errorPool.Get()
+	*ret = *o
+	return ret
+}
+
 func (o Error) MarshalBinary() ([]byte, error) {
 	return o.Dat, nil
 }
@@ -43,41 +63,58 @@ func UnmarshalItem(key btrfsprim.Key, csumType btrfssum.CSumType, dat []byte) It
 		var ok bool
 		gotyp, ok = untypedObjID2gotype[key.ObjectID]
 		if !ok {
-			return &Error{
+			ret, _ := errorPool.Get()
+			*ret = Error{
 				Dat: dat,
 				Err: fmt.Errorf("btrfsitem.UnmarshalItem({ItemType:%v, ObjectID:%v}, dat): unknown object ID for untyped item",
 					key.ItemType, key.ObjectID),
 			}
+			return ret
 		}
 	} else {
 		var ok bool
 		gotyp, ok = keytype2gotype[key.ItemType]
 		if !ok {
-			return &Error{
+			ret, _ := errorPool.Get()
+			*ret = Error{
 				Dat: dat,
 				Err: fmt.Errorf("btrfsitem.UnmarshalItem({ItemType:%v}, dat): unknown item type", key.ItemType),
 			}
+			return ret
 		}
 	}
-	ptr := reflect.New(gotyp)
-	if csums, ok := ptr.Interface().(*ExtentCSum); ok {
+	ptr, _ := gotype2pool[gotyp].Get()
+	if csums, ok := ptr.(*ExtentCSum); ok {
 		csums.ChecksumSize = csumType.Size()
 		csums.Addr = btrfsvol.LogicalAddr(key.Offset)
 	}
-	n, err := binstruct.Unmarshal(dat, ptr.Interface())
+	n, err := binstruct.Unmarshal(dat, ptr)
 	if err != nil {
-		return &Error{
+		ptr.Free()
+		ret, _ := errorPool.Get()
+		*ret = Error{
 			Dat: dat,
 			Err: fmt.Errorf("btrfsitem.UnmarshalItem({ItemType:%v}, dat): %w", key.ItemType, err),
 		}
+		return ret
 	}
 	if n < len(dat) {
-		return &Error{
+		ptr.Free()
+		ret, _ := errorPool.Get()
+		*ret = Error{
 			Dat: dat,
 			Err: fmt.Errorf("btrfsitem.UnmarshalItem({ItemType:%v}, dat): left over data: got %v bytes but only consumed %v",
 				key.ItemType, len(dat), n),
 		}
+		return ret
 	}
-	//nolint:forcetypeassert // items_gen.go has all types in keytype2gotype implement the Item interface.
-	return ptr.Interface().(Item)
+	return ptr
+}
+
+var bytePool containers.SlicePool[byte]
+
+func cloneBytes(in []byte) []byte {
+	out := bytePool.Get(len(in))
+	copy(out, in)
+	return out
 }
diff --git a/lib/btrfs/btrfsitem/items_gen.go b/lib/btrfs/btrfsitem/items_gen.go
index 8074610..31d2a76 100644
--- a/lib/btrfs/btrfsitem/items_gen.go
+++ b/lib/btrfs/btrfsitem/items_gen.go
@@ -5,6 +5,8 @@ package btrfsitem
 import (
 	"reflect"
 
+	"git.lukeshu.com/go/typedsync"
+
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
 )
 
@@ -110,6 +112,62 @@ var untypedObjID2gotype = map[btrfsprim.ObjID]reflect.Type{
 	btrfsprim.FREE_SPACE_OBJECTID: freeSpaceHeaderType,
 }
 
+// Pools.
+var (
+	blockGroupPool      = typedsync.Pool[Item]{New: func() Item { return new(BlockGroup) }}
+	chunkPool           = typedsync.Pool[Item]{New: func() Item { return new(Chunk) }}
+	devPool             = typedsync.Pool[Item]{New: func() Item { return new(Dev) }}
+	devExtentPool       = typedsync.Pool[Item]{New: func() Item { return new(DevExtent) }}
+	devStatsPool        = typedsync.Pool[Item]{New: func() Item { return new(DevStats) }}
+	dirEntryPool        = typedsync.Pool[Item]{New: func() Item { return new(DirEntry) }}
+	emptyPool           = typedsync.Pool[Item]{New: func() Item { return new(Empty) }}
+	extentPool          = typedsync.Pool[Item]{New: func() Item { return new(Extent) }}
+	extentCSumPool      = typedsync.Pool[Item]{New: func() Item { return new(ExtentCSum) }}
+	extentDataRefPool   = typedsync.Pool[Item]{New: func() Item { return new(ExtentDataRef) }}
+	fileExtentPool      = typedsync.Pool[Item]{New: func() Item { return new(FileExtent) }}
+	freeSpaceBitmapPool = typedsync.Pool[Item]{New: func() Item { return new(FreeSpaceBitmap) }}
+	freeSpaceHeaderPool = typedsync.Pool[Item]{New: func() Item { return new(FreeSpaceHeader) }}
+	freeSpaceInfoPool   = typedsync.Pool[Item]{New: func() Item { return new(FreeSpaceInfo) }}
+	inodePool           = typedsync.Pool[Item]{New: func() Item { return new(Inode) }}
+	inodeRefsPool       = typedsync.Pool[Item]{New: func() Item { return new(InodeRefs) }}
+	metadataPool        = typedsync.Pool[Item]{New: func() Item { return new(Metadata) }}
+	qGroupInfoPool      = typedsync.Pool[Item]{New: func() Item { return new(QGroupInfo) }}
+	qGroupLimitPool     = typedsync.Pool[Item]{New: func() Item { return new(QGroupLimit) }}
+	qGroupStatusPool    = typedsync.Pool[Item]{New: func() Item { return new(QGroupStatus) }}
+	rootPool            = typedsync.Pool[Item]{New: func() Item { return new(Root) }}
+	rootRefPool         = typedsync.Pool[Item]{New: func() Item { return new(RootRef) }}
+	sharedDataRefPool   = typedsync.Pool[Item]{New: func() Item { return new(SharedDataRef) }}
+	uuidMapPool         = typedsync.Pool[Item]{New: func() Item { return new(UUIDMap) }}
+)
+
+// gotype2pool is used by UnmarshalItem.
+var gotype2pool = map[reflect.Type]*typedsync.Pool[Item]{
+	blockGroupType:      &blockGroupPool,
+	chunkType:           &chunkPool,
+	devType:             &devPool,
+	devExtentType:       &devExtentPool,
+	devStatsType:        &devStatsPool,
+	dirEntryType:        &dirEntryPool,
+	emptyType:           &emptyPool,
+	extentType:          &extentPool,
+	extentCSumType:      &extentCSumPool,
+	extentDataRefType:   &extentDataRefPool,
+	fileExtentType:      &fileExtentPool,
+	freeSpaceBitmapType: &freeSpaceBitmapPool,
+	freeSpaceHeaderType: &freeSpaceHeaderPool,
+	freeSpaceInfoType:   &freeSpaceInfoPool,
+	inodeType:           &inodePool,
+	inodeRefsType:       &inodeRefsPool,
+	metadataType:        &metadataPool,
+	qGroupInfoType:      &qGroupInfoPool,
+	qGroupLimitType:     &qGroupLimitPool,
+	qGroupStatusType:    &qGroupStatusPool,
+	rootType:            &rootPool,
+	rootRefType:         &rootRefPool,
+	sharedDataRefType:   &sharedDataRefPool,
+	uuidMapType:         &uuidMapPool,
+}
+
 // isItem implements Item.
 func (*BlockGroup) isItem()      {}
 func (*Chunk) isItem()           {}
@@ -136,7 +194,145 @@ func (*RootRef) isItem()         {}
 func (*SharedDataRef) isItem()   {}
 func (*UUIDMap) isItem()         {}
 
-// Type assertions.
+// Free implements Item.
+func (o *BlockGroup) Free()      { *o = BlockGroup{}; blockGroupPool.Put(o) }
+func (o *Dev) Free()             { *o = Dev{}; devPool.Put(o) }
+func (o *DevExtent) Free()       { *o = DevExtent{}; devExtentPool.Put(o) }
+func (o *DevStats) Free()        { *o = DevStats{}; devStatsPool.Put(o) }
+func (o *Empty) Free()           { *o = Empty{}; emptyPool.Put(o) }
+func (o *ExtentCSum) Free()      { *o = ExtentCSum{}; extentCSumPool.Put(o) }
+func (o *ExtentDataRef) Free()   { *o = ExtentDataRef{}; extentDataRefPool.Put(o) }
+func (o *FreeSpaceHeader) Free() { *o = FreeSpaceHeader{}; freeSpaceHeaderPool.Put(o) }
+func (o *FreeSpaceInfo) Free()   { *o = FreeSpaceInfo{}; freeSpaceInfoPool.Put(o) }
+func (o *Inode) Free()           { *o = Inode{}; inodePool.Put(o) }
+func (o *QGroupInfo) Free()      { *o = QGroupInfo{}; qGroupInfoPool.Put(o) }
+func (o *QGroupLimit) Free()     { *o = QGroupLimit{}; qGroupLimitPool.Put(o) }
+func (o *QGroupStatus) Free()    { *o = QGroupStatus{}; qGroupStatusPool.Put(o) }
+func (o *Root) Free()            { *o = Root{}; rootPool.Put(o) }
+func (o *SharedDataRef) Free()   { *o = SharedDataRef{}; sharedDataRefPool.Put(o) }
+func (o *UUIDMap) Free()         { *o = UUIDMap{}; uuidMapPool.Put(o) }
+
+// Clone is a handy method.
+func (o BlockGroup) Clone() BlockGroup           { return o }
+func (o Dev) Clone() Dev                         { return o }
+func (o DevExtent) Clone() DevExtent             { return o }
+func (o DevStats) Clone() DevStats               { return o }
+func (o Empty) Clone() Empty                     { return o }
+func (o ExtentCSum) Clone() ExtentCSum           { return o }
+func (o ExtentDataRef) Clone() ExtentDataRef     { return o }
+func (o FreeSpaceHeader) Clone() FreeSpaceHeader { return o }
+func (o FreeSpaceInfo) Clone() FreeSpaceInfo     { return o }
+func (o Inode) Clone() Inode                     { return o }
+func (o QGroupInfo) Clone() QGroupInfo           { return o }
+func (o QGroupLimit) Clone() QGroupLimit         { return o }
+func (o QGroupStatus) Clone() QGroupStatus       { return o }
+func (o Root) Clone() Root                       { return o }
+func (o SharedDataRef) Clone() SharedDataRef     { return o }
+func (o UUIDMap) Clone() UUIDMap                 { return o }
+
+// CloneItem implements Item.
+func (o *BlockGroup) CloneItem() Item {
+	ret, _ := blockGroupPool.Get()
+	*(ret.(*BlockGroup)) = o.Clone()
+	return ret
+}
+func (o *Chunk) CloneItem() Item { ret, _ := chunkPool.Get(); *(ret.(*Chunk)) = o.Clone(); return ret }
+func (o *Dev) CloneItem() Item   { ret, _ := devPool.Get(); *(ret.(*Dev)) = o.Clone(); return ret }
+func (o *DevExtent) CloneItem() Item {
+	ret, _ := devExtentPool.Get()
+	*(ret.(*DevExtent)) = o.Clone()
+	return ret
+}
+func (o *DevStats) CloneItem() Item {
+	ret, _ := devStatsPool.Get()
+	*(ret.(*DevStats)) = o.Clone()
+	return ret
+}
+func (o *DirEntry) CloneItem() Item {
+	ret, _ := dirEntryPool.Get()
+	*(ret.(*DirEntry)) = o.Clone()
+	return ret
+}
+func (o *Empty) CloneItem() Item { ret, _ := emptyPool.Get(); *(ret.(*Empty)) = o.Clone(); return ret }
+func (o *Extent) CloneItem() Item {
+	ret, _ := extentPool.Get()
+	*(ret.(*Extent)) = o.Clone()
+	return ret
+}
+func (o *ExtentCSum) CloneItem() Item {
+	ret, _ := extentCSumPool.Get()
+	*(ret.(*ExtentCSum)) = o.Clone()
+	return ret
+}
+func (o *ExtentDataRef) CloneItem() Item {
+	ret, _ := extentDataRefPool.Get()
+	*(ret.(*ExtentDataRef)) = o.Clone()
+	return ret
+}
+func (o *FileExtent) CloneItem() Item {
+	ret, _ := fileExtentPool.Get()
+	*(ret.(*FileExtent)) = o.Clone()
+	return ret
+}
+func (o *FreeSpaceBitmap) CloneItem() Item {
+	ret, _ := freeSpaceBitmapPool.Get()
+	*(ret.(*FreeSpaceBitmap)) = o.Clone()
+	return ret
+}
+func (o *FreeSpaceHeader) CloneItem() Item {
+	ret, _ := freeSpaceHeaderPool.Get()
+	*(ret.(*FreeSpaceHeader)) = o.Clone()
+	return ret
+}
+func (o *FreeSpaceInfo) CloneItem() Item {
+	ret, _ := freeSpaceInfoPool.Get()
+	*(ret.(*FreeSpaceInfo)) = o.Clone()
+	return ret
+}
+func (o *Inode) CloneItem() Item { ret, _ := inodePool.Get(); *(ret.(*Inode)) = o.Clone(); return ret }
+func (o *InodeRefs) CloneItem() Item {
+	ret, _ := inodeRefsPool.Get()
+	*(ret.(*InodeRefs)) = o.Clone()
+	return ret
+}
+func (o *Metadata) CloneItem() Item {
+	ret, _ := metadataPool.Get()
+	*(ret.(*Metadata)) = o.Clone()
+	return ret
+}
+func (o *QGroupInfo) CloneItem() Item {
+	ret, _ := qGroupInfoPool.Get()
+	*(ret.(*QGroupInfo)) = o.Clone()
+	return ret
+}
+func (o *QGroupLimit) CloneItem() Item {
+	ret, _ := qGroupLimitPool.Get()
+	*(ret.(*QGroupLimit)) = o.Clone()
+	return ret
+}
+func (o *QGroupStatus) CloneItem() Item {
+	ret, _ := qGroupStatusPool.Get()
+	*(ret.(*QGroupStatus)) = o.Clone()
+	return ret
+}
+func (o *Root) CloneItem() Item { ret, _ := rootPool.Get(); *(ret.(*Root)) = o.Clone(); return ret }
+func (o *RootRef) CloneItem() Item {
+	ret, _ := rootRefPool.Get()
+	*(ret.(*RootRef)) = o.Clone()
+	return ret
+}
+func (o *SharedDataRef) CloneItem() Item {
+	ret, _ := sharedDataRefPool.Get()
+	*(ret.(*SharedDataRef)) = o.Clone()
+	return ret
+}
+func (o *UUIDMap) CloneItem() Item {
+	ret, _ := uuidMapPool.Get()
+	*(ret.(*UUIDMap)) = o.Clone()
+	return ret
+}
+
+// Item type assertions.
 var (
 	_ Item = (*BlockGroup)(nil)
 	_ Item = (*Chunk)(nil)
@@ -163,3 +359,31 @@ var (
 	_ Item = (*SharedDataRef)(nil)
 	_ Item = (*UUIDMap)(nil)
 )
+
+// Clone type assertions.
+var (
+	_ interface{ Clone() BlockGroup }      = BlockGroup{}
+	_ interface{ Clone() Chunk }           = Chunk{}
+	_ interface{ Clone() Dev }             = Dev{}
+	_ interface{ Clone() DevExtent }       = DevExtent{}
+	_ interface{ Clone() DevStats }        = DevStats{}
+	_ interface{ Clone() DirEntry }        = DirEntry{}
+	_ interface{ Clone() Empty }           = Empty{}
+	_ interface{ Clone() Extent }          = Extent{}
+	_ interface{ Clone() ExtentCSum }      = ExtentCSum{}
+	_ interface{ Clone() ExtentDataRef }   = ExtentDataRef{}
+	_ interface{ Clone() FileExtent }      = FileExtent{}
+	_ interface{ Clone() FreeSpaceBitmap } = FreeSpaceBitmap{}
+	_ interface{ Clone() FreeSpaceHeader } = FreeSpaceHeader{}
+	_ interface{ Clone() FreeSpaceInfo }   = FreeSpaceInfo{}
+	_ interface{ Clone() Inode }           = Inode{}
+	_ interface{ Clone() InodeRefs }       = InodeRefs{}
+	_ interface{ Clone() Metadata }        = Metadata{}
+	_ interface{ Clone() QGroupInfo }      = QGroupInfo{}
+	_ interface{ Clone() QGroupLimit }     = QGroupLimit{}
+	_ interface{ Clone() QGroupStatus }    = QGroupStatus{}
+	_ interface{ Clone() Root }            = Root{}
+	_ interface{ Clone() RootRef }         = RootRef{}
+	_ interface{ Clone() SharedDataRef }   = SharedDataRef{}
+	_ interface{ Clone() UUIDMap }         = UUIDMap{}
+)
diff --git a/lib/btrfs/io4_fs.go b/lib/btrfs/io4_fs.go
index c21cafc..56cf266 100644
--- a/lib/btrfs/io4_fs.go
+++ b/lib/btrfs/io4_fs.go
@@ -89,7 +89,7 @@ func (sv *Subvolume) init() {
 		} else {
 			switch rootBody := root.Body.(type) {
 			case *btrfsitem.Root:
-				sv.rootVal = *rootBody
+				sv.rootVal = rootBody.Clone()
 			case *btrfsitem.Error:
 				sv.rootErr = fmt.Errorf("FS_TREE ROOT_ITEM has malformed body: %w", rootBody.Err)
 			default:
@@ -127,7 +127,7 @@ func (sv *Subvolume) LoadBareInode(inode btrfsprim.ObjID) (*BareInode, error) {
 
 		switch itemBody := item.Body.(type) {
 		case *btrfsitem.Inode:
-			bodyCopy := *itemBody
+			bodyCopy := itemBody.Clone()
 			val.InodeItem = &bodyCopy
 		case *btrfsitem.Error:
 			val.Errs = append(val.Errs, fmt.Errorf("malformed inode: %w", itemBody.Err))
@@ -172,7 +172,7 @@ func (sv *Subvolume) LoadFullInode(inode btrfsprim.ObjID) (*FullInode, error) {
 						}
 						continue
 					}
-					bodyCopy := *itemBody
+					bodyCopy := itemBody.Clone()
 					val.InodeItem = &bodyCopy
 				case *btrfsitem.Error:
 					val.Errs = append(val.Errs, fmt.Errorf("malformed INODE_ITEM: %w", itemBody.Err))
@@ -264,7 +264,7 @@ func (dir *Dir) populate() {
 					}
 					continue
 				}
-				dir.ChildrenByName[string(entry.Name)] = *entry
+				dir.ChildrenByName[string(entry.Name)] = entry.Clone()
 			case *btrfsitem.Error:
 				dir.Errs = append(dir.Errs, fmt.Errorf("malformed DIR_ITEM: %w", entry.Err))
 			default:
@@ -280,7 +280,7 @@ func (dir *Dir) populate() {
 					}
 					continue
 				}
-				dir.ChildrenByIndex[index] = *entry
+				dir.ChildrenByIndex[index] = entry.Clone()
 			case *btrfsitem.Error:
 				dir.Errs = append(dir.Errs, fmt.Errorf("malformed DIR_INDEX: %w", entry.Err))
 			default:
diff --git a/lib/containers/slicepool.go b/lib/containers/slicepool.go
new file mode 100644
index 0000000..861691a
--- /dev/null
+++ b/lib/containers/slicepool.go
@@ -0,0 +1,35 @@
+// Copyright (C) 2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package containers
+
+import (
+	"git.lukeshu.com/go/typedsync"
+)
+
+type SlicePool[T any] struct {
+	// TODO(lukeshu): Consider bucketing slices by size, to
+	// increase odds that the `cap(ret) >= size` check passes.
+	inner typedsync.Pool[[]T]
+}
+
+func (p *SlicePool[T]) Get(size int) []T {
+	if size == 0 {
+		return nil
+	}
+	ret, ok := p.inner.Get()
+	if ok && cap(ret) >= size {
+		ret = ret[:size]
+	} else {
+		ret = make([]T, size)
+	}
+	return ret
+}
+
+func (p *SlicePool[T]) Put(slice []T) {
+	if slice == nil {
+		return
+	}
+	p.inner.Put(slice)
+}