⚡ Bolt: optimize format! allocation in procfs - #18
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Replaced `format!` macros inside `procfs` with pre-allocated `String::with_capacity` and `write!` macros for complex formatted strings, and `to_string()` for simple integers. This prevents the default dynamic allocation overhead incurred by `format!` inside hot paths, specifically when parsing PIDs and FDs. Co-authored-by: muou000 <77525792+muou000@users.noreply.github.com>
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📝 WalkthroughWalkthroughThis PR simplifies string construction in the procfs module by eliminating the ChangesProcfs String Formatting Refactoring
Estimated code review effort🎯 2 (Simple) | ⏱️ ~8 minutes Poem
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Code Review
This pull request optimizes string formatting in procfs.rs by replacing format! macros with .to_string() and pre-allocated strings using write!. A review comment points out that calling to_string() followed by pushing a newline character on PID_MAX triggers an unnecessary reallocation, and suggests using write! with a pre-allocated string of capacity 12 to avoid this.
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| let mut s = PID_MAX.load(core::sync::atomic::Ordering::Acquire).to_string(); | ||
| s.push('\n'); | ||
| s |
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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));
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Pull request overview
Optimizes string construction in the procfs implementation to reduce transient heap allocations when serving common /proc reads, replacing several format! usages with more allocation-aware alternatives.
Changes:
- Replaced integer
format!calls (e.g., for PIDs/FDs) withto_string(). - Reworked
/proc/meminforendering to preallocate aStringand populate it viawrite!. - Avoided
format!("{}\n", ...)by appending\nonto an existing string.
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💡 What: Replaced inefficient
format!macro calls withinarceos/modules/axfs/src/fs/procfs.rswith more optimal alternatives.to_string()for integer formatting which natively relies on fastitoaoperations instead of macro-generated structures.String::with_capacity(128)and thewrite!macro for complex layout strings (e.g.MemInfo).🎯 Why: To improve performance and minimize unnecessary memory heap allocations when serving standard Linux process/system file accesses.
format!dynamically allocates on the heap without knowing its maximum capacity beforehand, whereas statically sizing strings minimizes reallocations.📊 Impact: Reduces transient dynamic memory allocation calls when fetching process file descriptors, meminfo, and enumerating processes. Expected to save CPU cycles and reduce fragmentation on system operations reading
/proc.🔬 Measurement: Verify tests run cleanly on
riscv64andloongarch64builds usingmake test.PR created automatically by Jules for task 5448303405494560997 started by @muou000
Summary by CodeRabbit