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Reduce short-lived allocations in memory maps parsing #331

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Reduce short-lived allocations in memory maps parsing #331

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22 changes: 17 additions & 5 deletions procfs-core/src/process/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -489,12 +489,24 @@ pub struct MemoryMaps(pub Vec<MemoryMap>);

impl crate::FromBufRead for MemoryMaps {
/// The data should be formatted according to procfs /proc/pid/{maps,smaps,smaps_rollup}.
fn from_buf_read<R: BufRead>(reader: R) -> ProcResult<Self> {
let mut memory_maps = Vec::new();

let mut line_iter = reader.lines().map(|r| r.map_err(|_| ProcError::Incomplete(None)));
fn from_buf_read<R: BufRead>(mut reader: R) -> ProcResult<Self> {
let mut memory_maps = Vec::with_capacity(10);
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This was an educate guess that I cross-checked with my dev box:

$ for maps in /proc/*/maps; do sudo cat $maps | wc -l; done 2>/dev/null | grep -v 0 | sort | uniq -c | sort -k2h
      6 23
      1 26
     12 31
      1 33
      2 36
      2 45
      2 57
      1 59
      1 63
      1 78
      1 82
      1 83
[...]

let mut current_memory_map: Option<MemoryMap> = None;
while let Some(line) = line_iter.next().transpose()? {
let mut line = String::with_capacity(100);
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Based on:

len("55fa56b4f000-55fa56b51000 r--p 00000000 00:1f 5749885190                 /usr/bin/cat")
85


loop {
line.clear();
match reader.read_line(&mut line) {
// End of file.
Ok(0) => break,
Ok(_) => {},
Err(_) => return Err(ProcError::Incomplete(None)),
}

if line.is_empty() {
break;
}

// Assumes all extension fields (in `/proc/<pid>/smaps`) start with a capital letter,
// which seems to be the case.
if line.starts_with(|c: char| c.is_ascii_uppercase()) {
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