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⚡ Bolt: optimize format! allocation in procfs #18

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⚡ Bolt: optimize format! allocation in procfs #18

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27 changes: 14 additions & 13 deletions arceos/modules/axfs/src/fs/procfs.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
use alloc::{borrow::ToOwned, collections::BTreeMap, format, string::String, sync::Arc, vec::Vec};
use alloc::{borrow::ToOwned, collections::BTreeMap, string::{String, ToString}, sync::Arc, vec::Vec};
use core::{
any::Any,
borrow::Borrow,
Expand Down Expand Up @@ -475,7 +475,7 @@ impl ProcFilesystem {

if let Some(fds) = provider.process_fds(pid) {
for fd in fds {
let name = format!("{}", fd);
let name = fd.to_string();
let child_ino = PID_INODE_START + (pid << PID_INODE_SHIFT) + SUB_INO_FD_BASE + fd as u64;
entries.insert(name.into(), InodeRef::new(child_ino));
}
Expand Down Expand Up @@ -606,12 +606,11 @@ fn render_meminfo() -> String {
let mem_free = free_bytes.min(total_bytes);
let mem_available = mem_free;

format!(
"MemTotal: {:>8} kB\nMemFree: {:>9} kB\nMemAvailable: {:>4} kB\n",
to_kib(total_bytes),
to_kib(mem_free),
to_kib(mem_available)
)
use core::fmt::Write;
let mut s = String::with_capacity(128);
let _ = write!(&mut s, "MemTotal: {:>8} kB\nMemFree: {:>9} kB\nMemAvailable: {:>4} kB\n",
to_kib(total_bytes), to_kib(mem_free), to_kib(mem_available));
s
}

fn render_mounts() -> String {
Expand Down Expand Up @@ -647,7 +646,7 @@ fn render_proc_file(fs: &ProcFilesystem, kind: ProcLiveFileKind) -> String {
ProcLiveFileKind::SelfSymlink => {
if let Some(provider) = PROCESS_PROVIDER.get() {
if let Some(pid) = provider.current_pid() {
return format!("{}", pid);
return pid.to_string();
}
}
"1".to_owned()
Expand All @@ -656,7 +655,7 @@ fn render_proc_file(fs: &ProcFilesystem, kind: ProcLiveFileKind) -> String {
if let Some(provider) = PROCESS_PROVIDER.get() {
let pids = provider.process_pids();
if let Some(&min_pid) = pids.iter().min() {
return format!("{}", min_pid);
return min_pid.to_string();
}
}
"1".to_owned()
Expand Down Expand Up @@ -695,7 +694,9 @@ fn render_proc_file(fs: &ProcFilesystem, kind: ProcLiveFileKind) -> String {
fs.gid_map_map.lock().get(&pid).cloned().unwrap_or_default()
}
ProcLiveFileKind::PidMax => {
format!("{}\n", PID_MAX.load(core::sync::atomic::Ordering::Acquire))
let mut s = PID_MAX.load(core::sync::atomic::Ordering::Acquire).to_string();
s.push('\n');
s
Comment on lines +697 to +699

@gemini-code-assist gemini-code-assist Bot Jun 4, 2026

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medium

Calling to_string() on an integer typically allocates a String with a capacity exactly matching the length of the formatted number. Consequently, calling s.push('\n') immediately after will trigger a reallocation and copy the string data, which defeats the optimization goal of this PR.

Using write! with a pre-allocated String of capacity 12 (sufficient for any u32 plus a newline) avoids this reallocation entirely.

            use core::fmt::Write;
            let mut s = String::with_capacity(12);
            let _ = write!(&mut s, "{}\n", PID_MAX.load(core::sync::atomic::Ordering::Acquire));
            s

}
ProcLiveFileKind::Filesystems => render_filesystems(),
ProcLiveFileKind::Tainted => {
Expand Down Expand Up @@ -906,7 +907,7 @@ impl DirNodeOps for ProcNode {

if let Some(fds) = provider.process_fds(pid) {
for fd in fds {
let name = format!("{}", fd);
let name = fd.to_string();
let child_ino = PID_INODE_START + (pid << PID_INODE_SHIFT) + SUB_INO_FD_BASE + fd as u64;
all_entries.push((name, child_ino));
}
Expand All @@ -922,7 +923,7 @@ impl DirNodeOps for ProcNode {
if self.ino == ROOT_INO {
if let Some(provider) = PROCESS_PROVIDER.get() {
for pid in provider.process_pids() {
let name = format!("{}", pid);
let name = pid.to_string();
let child_ino = PID_INODE_START + (pid << PID_INODE_SHIFT) + SUB_INO_DIR;
all_entries.push((name, child_ino));
}
Expand Down