pkg/buffer: Reorganize internal structure to allow dynamic sizes.

This change changes `buffer.data` into a `[]byte`, from `[bufferSize]byte`.
In exchange, each `buffer` is now grouped together to reduce the number of
allocation. Plus, `View` now holds an embeded list of `buffer` (via `pool`) to
support the happy path which the number of buffer is small. Expect no extra
allocation for the happy path.

It is to enable the use case for PacketBuffer, which
* each `View` is small (way less than `defaultBufferSize`), and
* needs to dynamically transfer ownership of `[]byte` to `View`.
  (to allow gradual migration)

PiperOrigin-RevId: 333197252

1 files changed, 9 insertions, 26 deletions

diff --git a/pkg/buffer/buffer.go b/pkg/buffer/buffer.go
index c6d089fd9..311808ae9 100644
--- a/pkg/buffer/buffer.go
+++ b/pkg/buffer/buffer.go
@@ -14,36 +14,26 @@
 
 // Package buffer provides the implementation of a buffer view.
 //
-// A view is an flexible buffer, backed by a pool, supporting the safecopy
-// operations natively as well as the ability to grow via either prepend or
-// append, as well as shrink.
+// A view is an flexible buffer, supporting the safecopy operations natively as
+// well as the ability to grow via either prepend or append, as well as shrink.
 package buffer
 
-import (
-	"sync"
-)
-
-const bufferSize = 8144 // See below.
-
 // buffer encapsulates a queueable byte buffer.
 //
-// Note that the total size is slightly less than two pages. This is done
-// intentionally to ensure that the buffer object aligns with runtime
-// internals. We have no hard size or alignment requirements. This two page
-// size will effectively minimize internal fragmentation, but still have a
-// large enough chunk to limit excessive segmentation.
-//
 // +stateify savable
 type buffer struct {
-	data  [bufferSize]byte
+	data  []byte
 	read  int
 	write int
 	bufferEntry
 }
 
-// reset resets internal data.
-//
-// This must be called before returning the buffer to the pool.
+// init performs in-place initialization for zero value.
+func (b *buffer) init(size int) {
+	b.data = make([]byte, size)
+}
+
+// Reset resets read and write locations, effectively emptying the buffer.
 func (b *buffer) Reset() {
 	b.read = 0
 	b.write = 0
@@ -85,10 +75,3 @@ func (b *buffer) WriteMove(n int) {
 func (b *buffer) WriteSlice() []byte {
 	return b.data[b.write:]
 }
-
-// bufferPool is a pool for buffers.
-var bufferPool = sync.Pool{
-	New: func() interface{} {
-		return new(buffer)
-	},
-}