buffer: increase Buffer.poolSize default to 64 KiB

The 8 KiB default has been unchanged since 2015. With the threshold
check `size < (Buffer.poolSize >>> 1)`, this means allocations of 4 KiB
or larger bypass the pool entirely — including 4 KiB itself, a common
page and HTTP-frame size.

Raising the default to 64 KiB extends pool coverage to ~32 KiB
allocations, capturing common sizes used by HTTP parsers, stream
chunks, and small file reads.

Throughput improvements on workers-k=8 fs.readFileSync benchmarks
(Linux/glibc) at the affected sizes, with no regressions elsewhere:

  file size  |  8 KiB pool  |  64 KiB pool  |  delta
  -----------+--------------+---------------+-------
   4 KiB     |  326k ops/s  |  360k ops/s   |  +10%
   8 KiB     |  202k ops/s  |  254k ops/s   |  +26%
  16 KiB     |  148k ops/s  |  181k ops/s   |  +23%
  64 KiB     |   86k ops/s  |   87k ops/s   |   ~
   1 MiB     |   12k ops/s  |   13k ops/s   |   ~

Cost: +56 KiB RSS per realm at startup.
Signed-off-by: Matteo Collina <hello@matteocollina.com>
PR-URL: #63597
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: LiviaMedeiros <livia@cirno.name>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>

Author: mcollina

doc/api/buffer.md

@@ -865,7 +865,7 @@ _may contain sensitive data_. Use [`buf.fill(0)`][`buf.fill()`] to initialize
 such `Buffer` instances with zeroes.
 
 When using [`Buffer.allocUnsafe()`][] to allocate new `Buffer` instances,
-allocations less than `Buffer.poolSize >>> 1` (4KiB when default poolSize is used) are sliced
+allocations less than `Buffer.poolSize >>> 1` (32KiB when default poolSize is used) are sliced
 from a single pre-allocated `Buffer`. This allows applications to avoid the
 garbage collection overhead of creating many individually allocated `Buffer`
 instances. This approach improves both performance and memory usage by
@@ -1497,9 +1497,13 @@ console.log(Buffer.isEncoding(''));
 
 <!-- YAML
 added: v0.11.3
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/63597
+    description: Default raised from 8192 to 65536.
 -->
 
-* Type: {integer} **Default:** `8192`
+* Type: {integer} **Default:** `65536`
 
 This is the size (in bytes) of pre-allocated internal `Buffer` instances used
 for pooling. This value may be modified.

lib/buffer.js

@@ -150,7 +150,7 @@ const constants = ObjectDefineProperties({}, {
   },
 });
 
-Buffer.poolSize = 8 * 1024;
+Buffer.poolSize = 64 * 1024;
 let poolSize, poolOffset, allocPool, allocBuffer;
 
 function createPool() {