comparison rust/hg-core/src/dirstate_tree/status.rs @ 48745:94e36b230990

status: prefer relative paths in Rust code

… when the repository root is under the current directory,
so the kernel needs to traverse fewer directory in every call
to `read_dir` or `symlink_metadata`.

Better yet would be to use libc functions like `openat` and `fstatat`
to remove such repeated traversals entirely, but the standard library
does not provide APIs based on those.
Maybe with a crate like https://crates.io/crates/openat instead?

Benchmarks of `rhg status` show that this patch is neutral in some configurations,
and makes the command up to ~20% faster in others.
Below is semi-arbitrary subset of results. The four numeric columns are:
time (in seconds) with this changeset’s parent, time with this changeset,
time difference (negative is better), time ratio (less than 1 is better).

```
mercurial-dirstate-v1 | default-plain-clean.no-iu.pbr            | 0.0061 -> 0.0059: -0.0002 (0.97)
mercurial-dirstate-v2 | default-plain-clean.no-iu.pbr            | 0.0029 -> 0.0028: -0.0001 (0.97)
mozilla-dirstate-v1   | default-plain-clean.no-iu.pbr            | 0.2110 -> 0.2102: -0.0007 (1.00)
mozilla-dirstate-v2   | default-copies-clean.ignored.pbr         | 0.0489 -> 0.0401: -0.0088 (0.82)
mozilla-dirstate-v2   | default-copies-clean.no-iu.pbr           | 0.0479 -> 0.0393: -0.0085 (0.82)
mozilla-dirstate-v2   | default-copies-large.all.pbr             | 0.1262 -> 0.1210: -0.0051 (0.96)
mozilla-dirstate-v2   | default-copies-small.ignored-unknown.pbr | 0.1262 -> 0.1200: -0.0062 (0.95)
mozilla-dirstate-v2   | default-copies-small.ignored.pbr         | 0.0536 -> 0.0417: -0.0119 (0.78)
mozilla-dirstate-v2   | default-copies-small.no-iu.pbr           | 0.0482 -> 0.0393: -0.0089 (0.81)
mozilla-dirstate-v2   | default-plain-clean.ignored.pbr          | 0.0518 -> 0.0402: -0.0116 (0.78)
mozilla-dirstate-v2   | default-plain-clean.no-iu.pbr            | 0.0481 -> 0.0392: -0.0088 (0.82)
mozilla-dirstate-v2   | default-plain-large.all.pbr              | 0.1271 -> 0.1218: -0.0052 (0.96)
mozilla-dirstate-v2   | default-plain-small.ignored-unknown.pbr  | 0.1225 -> 0.1202: -0.0022 (0.98)
mozilla-dirstate-v2   | default-plain-small.ignored.pbr          | 0.0510 -> 0.0418: -0.0092 (0.82)
mozilla-dirstate-v2   | default-plain-small.no-iu.pbr            | 0.0480 -> 0.0394: -0.0086 (0.82)
netbeans-dirstate-v1  | default-plain-clean.no-iu.pbr            | 0.1442 -> 0.1422: -0.0020 (0.99)
netbeans-dirstate-v2  | default-plain-clean.no-iu.pbr            | 0.0325 -> 0.0282: -0.0043 (0.87)
```

Differential Revision: https://phab.mercurial-scm.org/D12175

48744:6e930bc45aeb

            (Box::new(|&_| true), vec![], None)
        };

    let filesystem_time_at_status_start =
        filesystem_now(&root_dir).ok().map(TruncatedTimestamp::from);
    let outcome = DirstateStatus {
        filesystem_time_at_status_start,
        ..Default::default()
    };
    let common = StatusCommon {

    ///
    /// * At the repository root, ignore that sub-directory
    /// * Elsewhere, we’re listing the content of a sub-repo. Return an empty
    ///   list instead.
    fn read_dir(path: &Path, is_at_repo_root: bool) -> io::Result<Vec<Self>> {
        let mut results = Vec::new();
        for entry in path.read_dir()? {
            let entry = entry?;
            let metadata = entry.metadata()?;
            let name = get_bytes_from_os_string(entry.file_name());
            // FIXME don't do this when cached
            if name == b".hg" {
                if is_at_repo_root {
                    // Skip the repo’s own .hg (might be a symlink)
                    continue;
                } else if metadata.is_dir() {
                    // A .hg sub-directory at another location means a subrepo,
                    // skip it entirely.
                    return Ok(Vec::new());
                }
            }
            results.push(DirEntry {
                base_name: name.into(),
                full_path: entry.path(),
                metadata,
            })
        }
        Ok(results)
    }

48745:94e36b230990

            (Box::new(|&_| true), vec![], None)
        };

    let filesystem_time_at_status_start =
        filesystem_now(&root_dir).ok().map(TruncatedTimestamp::from);

    // If the repository is under the current directory, prefer using a
    // relative path, so the kernel needs to traverse fewer directory in every
    // call to `read_dir` or `symlink_metadata`.
    // This is effective in the common case where the current directory is the
    // repository root.

    // TODO: Better yet would be to use libc functions like `openat` and
    // `fstatat` to remove such repeated traversals entirely, but the standard
    // library does not provide APIs based on those.
    // Maybe with a crate like https://crates.io/crates/openat instead?
    let root_dir = if let Some(relative) = std::env::current_dir()
        .ok()
        .and_then(|cwd| root_dir.strip_prefix(cwd).ok())
    {
        relative
    } else {
        &root_dir
    };

    let outcome = DirstateStatus {
        filesystem_time_at_status_start,
        ..Default::default()
    };
    let common = StatusCommon {

    ///
    /// * At the repository root, ignore that sub-directory
    /// * Elsewhere, we’re listing the content of a sub-repo. Return an empty
    ///   list instead.
    fn read_dir(path: &Path, is_at_repo_root: bool) -> io::Result<Vec<Self>> {
        // `read_dir` returns a "not found" error for the empty path
        let at_cwd = path == Path::new("");
        let read_dir_path = if at_cwd { Path::new(".") } else { path };
        let mut results = Vec::new();
        for entry in read_dir_path.read_dir()? {
            let entry = entry?;
            let metadata = entry.metadata()?;
            let file_name = entry.file_name();
            // FIXME don't do this when cached
            if file_name == ".hg" {
                if is_at_repo_root {
                    // Skip the repo’s own .hg (might be a symlink)
                    continue;
                } else if metadata.is_dir() {
                    // A .hg sub-directory at another location means a subrepo,
                    // skip it entirely.
                    return Ok(Vec::new());
                }
            }
            let full_path = if at_cwd {
                file_name.clone().into()
            } else {
                entry.path()
            };
            let base_name = get_bytes_from_os_string(file_name).into();
            results.push(DirEntry {
                base_name,
                full_path,
                metadata,
            })
        }
        Ok(results)
    }