fs: improve fsPromises readFile performance

benchmark/fs/readfile-promises.js

@@ -0,0 +1,63 @@
+// Call fs.promises.readFile over and over again really fast.
+// Then see how many times it got called.
+// Yes, this is a silly benchmark.  Most benchmarks are silly.
+'use strict';
+
+const path = require('path');
+const common = require('../common.js');
+const fs = require('fs');
+const assert = require('assert');
+
+const tmpdir = require('../../test/common/tmpdir');
+tmpdir.refresh();
+const filename = path.resolve(tmpdir.path,
+                              `.removeme-benchmark-garbage-${process.pid}`);
+
+const bench = common.createBenchmark(main, {
+  duration: [5],
+  len: [1024, 16 * 1024 * 1024],
+  concurrent: [1, 10]
+});
+
+function main({ len, duration, concurrent }) {
+  try { fs.unlinkSync(filename); } catch { }
+  let data = Buffer.alloc(len, 'x');
+  fs.writeFileSync(filename, data);
+  data = null;
+
+  let writes = 0;
+  let benchEnded = false;
+  bench.start();
+  setTimeout(() => {
+    benchEnded = true;
+    bench.end(writes);
+    try { fs.unlinkSync(filename); } catch { }
+    process.exit(0);
+  }, duration * 1000);
+
+  function read() {
+    fs.promises.readFile(filename)
+      .then((res) => afterRead(undefined, res))
+      .catch((err) => afterRead(err));
+  }
+
+  function afterRead(er, data) {
+    if (er) {
+      if (er.code === 'ENOENT') {
+        // Only OK if unlinked by the timer from main.
+        assert.ok(benchEnded);
+        return;
+      }
+      throw er;
+    }
+
+    if (data.length !== len)
+      throw new Error('wrong number of bytes returned');
+
+    writes++;
+    if (!benchEnded)
+      read();
+  }
+
+  while (concurrent--) read();
+}

lib/internal/fs/promises.js

@@ -4,9 +4,8 @@
 // See https://github.com/libuv/libuv/pull/1501.
 const kIoMaxLength = 2 ** 31 - 1;
 
-// Note: This is different from kReadFileBufferLength used for non-promisified
-// fs.readFile.
-const kReadFileMaxChunkSize = 2 ** 14;
+const kReadFileBufferLength = 512 * 1024;
+const kReadFileUnknownBufferLength = 64 * 1024;
 const kWriteFileMaxChunkSize = 2 ** 14;
 
 const {
@@ -316,25 +315,46 @@ async function readFileHandle(filehandle, options) {
   if (size > kIoMaxLength)
     throw new ERR_FS_FILE_TOO_LARGE(size);
 
-  const chunks = [];
-  let isFirstChunk = true;
-  const firstChunkSize = size === 0 ? kReadFileMaxChunkSize : size;
-  const chunkSize = MathMin(firstChunkSize, kReadFileMaxChunkSize);
   let endOfFile = false;
+  let totalRead = 0;
+  const noSize = size === 0;
+  const buffers = [];
+  const fullBuffer = noSize ? undefined : Buffer.allocUnsafeSlow(size);
   do {
     if (signal?.aborted) {
       throw lazyDOMException('The operation was aborted', 'AbortError');
     }
-    const buf = Buffer.alloc(isFirstChunk ? firstChunkSize : chunkSize);
-    const { bytesRead, buffer } =
-      await read(filehandle, buf, 0, buf.length, -1);
-    endOfFile = bytesRead === 0;
-    if (bytesRead > 0)
-      ArrayPrototypePush(chunks, buffer.slice(0, bytesRead));
-    isFirstChunk = false;
+    let buffer;
+    let offset;
+    let length;
+    if (noSize) {
+      buffer = Buffer.allocUnsafeSlow(kReadFileUnknownBufferLength);
+      offset = 0;
+      length = kReadFileUnknownBufferLength;
+    } else {
+      buffer = fullBuffer;
+      offset = totalRead;
+      length = MathMin(size - totalRead, kReadFileBufferLength);
+    }
+
+    const bytesRead = (await binding.read(filehandle.fd, buffer, offset,
+                                          length, -1, kUsePromises)) || 0;
+    totalRead += bytesRead;
+    endOfFile = bytesRead === 0 || totalRead === size;
+    if (noSize && bytesRead > 0) {
+      const isBufferFull = bytesRead === kReadFileUnknownBufferLength;
+      const chunkBuffer = isBufferFull ? buffer : buffer.slice(0, bytesRead);
+      ArrayPrototypePush(buffers, chunkBuffer);
+    }
   } while (!endOfFile);
 
-  const result = chunks.length === 1 ? chunks[0] : Buffer.concat(chunks);
+  let result;
+  if (size > 0) {
+    result = totalRead === size ? fullBuffer : fullBuffer.slice(0, totalRead);
+  } else {
+    result = buffers.length === 1 ? buffers[0] : Buffer.concat(buffers,
+                                                               totalRead);
+  }
 
   return options.encoding ? result.toString(options.encoding) : result;
 }

test/parallel/test-fs-promises-file-handle-readFile.js

@@ -10,7 +10,7 @@ const {
   open,
   readFile,
   writeFile,
-  truncate
+  truncate,
 } = fs.promises;
 const path = require('path');
 const tmpdir = require('../common/tmpdir');
@@ -64,6 +64,7 @@ async function doReadAndCancel() {
     await assert.rejects(readFile(fileHandle, { signal }), {
       name: 'AbortError'
     });
+    await fileHandle.close();
   }
 
   // Signal aborted on first tick
@@ -74,10 +75,11 @@ async function doReadAndCancel() {
     fs.writeFileSync(filePathForHandle, buffer);
     const controller = new AbortController();
     const { signal } = controller;
-    tick(1, () => controller.abort());
+    process.nextTick(() => controller.abort());
     await assert.rejects(readFile(fileHandle, { signal }), {
       name: 'AbortError'
-    });
+    }, 'tick-0');
+    await fileHandle.close();
   }
 
   // Signal aborted right before buffer read
@@ -90,10 +92,12 @@ async function doReadAndCancel() {
 
     const controller = new AbortController();
     const { signal } = controller;
-    tick(2, () => controller.abort());
+    tick(1, () => controller.abort());
     await assert.rejects(fileHandle.readFile({ signal, encoding: 'utf8' }), {
       name: 'AbortError'
-    });
+    }, 'tick-1');
+
+    await fileHandle.close();
   }
 
   // Validate file size is within range for reading
@@ -111,6 +115,7 @@ async function doReadAndCancel() {
       name: 'RangeError',
       code: 'ERR_FS_FILE_TOO_LARGE'
     });
+    await fileHandle.close();
   }
 }