io: increase MAX_BUF from 16384 to 2MiB (#5397)

Author: brxken128

tokio/src/fs/file/tests.rs

@@ -231,12 +231,12 @@ fn flush_while_idle() {
 #[cfg_attr(miri, ignore)] // takes a really long time with miri
 fn read_with_buffer_larger_than_max() {
     // Chunks
-    let chunk_a = 16 * 1024;
+    let chunk_a = crate::io::blocking::MAX_BUF;
     let chunk_b = chunk_a * 2;
     let chunk_c = chunk_a * 3;
     let chunk_d = chunk_a * 4;
 
-    assert_eq!(chunk_d / 1024, 64);
+    assert_eq!(chunk_d / 1024 / 1024, 8);
 
     let mut data = vec![];
     for i in 0..(chunk_d - 1) {
@@ -303,12 +303,12 @@ fn read_with_buffer_larger_than_max() {
 #[cfg_attr(miri, ignore)] // takes a really long time with miri
 fn write_with_buffer_larger_than_max() {
     // Chunks
-    let chunk_a = 16 * 1024;
+    let chunk_a = crate::io::blocking::MAX_BUF;
     let chunk_b = chunk_a * 2;
     let chunk_c = chunk_a * 3;
     let chunk_d = chunk_a * 4;
 
-    assert_eq!(chunk_d / 1024, 64);
+    assert_eq!(chunk_d / 1024 / 1024, 8);
 
     let mut data = vec![];
     for i in 0..(chunk_d - 1) {

tokio/src/io/blocking.rs

@@ -26,7 +26,7 @@ pub(crate) struct Buf {
     pos: usize,
 }
 
-pub(crate) const MAX_BUF: usize = 16 * 1024;
+pub(crate) const MAX_BUF: usize = 2 * 1024 * 1024;
 
 #[derive(Debug)]
 enum State<T> {

tokio/src/io/stdio_common.rs

@@ -108,14 +108,13 @@ where
 #[cfg(test)]
 #[cfg(not(loom))]
 mod tests {
+    use crate::io::blocking::MAX_BUF;
     use crate::io::AsyncWriteExt;
     use std::io;
     use std::pin::Pin;
     use std::task::Context;
     use std::task::Poll;
 
-    const MAX_BUF: usize = 16 * 1024;
-
     struct TextMockWriter;
 
     impl crate::io::AsyncWrite for TextMockWriter {