dirstate-tree: Skip readdir() in `hg status -mard`

When running the status algorithm in a mode where we don’t list unknown
or ignored files, all we care about are files that are listed in the dirstate.
We can there for skip making expensive calls to readdir() to list the contents
of filesystem directories, and instead only run stat() to get the filesystem
state of files listed in the dirstate. (This state may be an error for files
that don’t exist anymore on the filesystem.)

On 16 CPU threads, this reduces the time spent in the `status()` function for
`hg status -mard` on an old snapshot of mozilla-central from ~70ms to ~50ms.

Differential Revision: https://phab.mercurial-scm.org/D10752

rust/hg-core/src/dirstate_tree/status.rs

@@ -1,433 +1,466 b''
 use crate::dirstate::status::IgnoreFnType;
 use crate::dirstate_tree::dirstate_map::ChildNodesRef;
 use crate::dirstate_tree::dirstate_map::DirstateMap;
 use crate::dirstate_tree::dirstate_map::NodeRef;
 use crate::dirstate_tree::on_disk::DirstateV2ParseError;
 use crate::matchers::get_ignore_function;
 use crate::matchers::Matcher;
 use crate::utils::files::get_bytes_from_os_string;
+use crate::utils::files::get_path_from_bytes;
 use crate::utils::hg_path::HgPath;
 use crate::BadMatch;
 use crate::DirstateStatus;
 use crate::EntryState;
 use crate::HgPathBuf;
 use crate::PatternFileWarning;
 use crate::StatusError;
 use crate::StatusOptions;
 use micro_timer::timed;
 use rayon::prelude::*;
 use std::borrow::Cow;
 use std::io;
 use std::path::Path;
 use std::path::PathBuf;
 use std::sync::Mutex;
 
 /// Returns the status of the working directory compared to its parent
 /// changeset.
 ///
 /// This algorithm is based on traversing the filesystem tree (`fs` in function
 /// and variable names) and dirstate tree at the same time. The core of this
 /// traversal is the recursive `traverse_fs_directory_and_dirstate` function
 /// and its use of `itertools::merge_join_by`. When reaching a path that only
 /// exists in one of the two trees, depending on information requested by
 /// `options` we may need to traverse the remaining subtree.
 #[timed]
 pub fn status<'tree, 'on_disk: 'tree>(
     dmap: &'tree mut DirstateMap<'on_disk>,
     matcher: &(dyn Matcher + Sync),
     root_dir: PathBuf,
     ignore_files: Vec<PathBuf>,
     options: StatusOptions,
 ) -> Result<(DirstateStatus<'tree>, Vec<PatternFileWarning>), StatusError> {
     let (ignore_fn, warnings): (IgnoreFnType, _) =
         if options.list_ignored || options.list_unknown {
             get_ignore_function(ignore_files, &root_dir)?
         } else {
             (Box::new(|&_| true), vec![])
         };
 
     let common = StatusCommon {
         dmap,
         options,
         matcher,
         ignore_fn,
         outcome: Mutex::new(DirstateStatus::default()),
     };
     let is_at_repo_root = true;
     let hg_path = HgPath::new("");
     let has_ignored_ancestor = false;
     common.traverse_fs_directory_and_dirstate(
         has_ignored_ancestor,
         dmap.root.as_ref(),
         hg_path,
         &root_dir,
         is_at_repo_root,
     )?;
     Ok((common.outcome.into_inner().unwrap(), warnings))
 }
 
 /// Bag of random things needed by various parts of the algorithm. Reduces the
 /// number of parameters passed to functions.
 struct StatusCommon<'tree, 'a, 'on_disk: 'tree> {
     dmap: &'tree DirstateMap<'on_disk>,
     options: StatusOptions,
     matcher: &'a (dyn Matcher + Sync),
     ignore_fn: IgnoreFnType<'a>,
     outcome: Mutex<DirstateStatus<'tree>>,
 }
 
 impl<'tree, 'a> StatusCommon<'tree, 'a, '_> {
     fn read_dir(
         &self,
         hg_path: &HgPath,
         fs_path: &Path,
         is_at_repo_root: bool,
     ) -> Result<Vec<DirEntry>, ()> {
-        DirEntry::read_dir(fs_path, is_at_repo_root).map_err(|error| {
+        DirEntry::read_dir(fs_path, is_at_repo_root)
+            .map_err(|error| self.io_error(error, hg_path))
+    }
+
+    fn io_error(&self, error: std::io::Error, hg_path: &HgPath) {
             let errno = error.raw_os_error().expect("expected real OS error");
             self.outcome
                 .lock()
                 .unwrap()
                 .bad
                 .push((hg_path.to_owned().into(), BadMatch::OsError(errno)))
-        })
     }
 
     fn traverse_fs_directory_and_dirstate(
         &self,
         has_ignored_ancestor: bool,
         dirstate_nodes: ChildNodesRef<'tree, '_>,
         directory_hg_path: &'tree HgPath,
         directory_fs_path: &Path,
         is_at_repo_root: bool,
     ) -> Result<(), DirstateV2ParseError> {
+        if !self.options.list_unknown && !self.options.list_ignored {
+            // We only care about files in the dirstate, so we can skip listing
+            // filesystem directories entirely.
+            return dirstate_nodes
+                .par_iter()
+                .map(|dirstate_node| {
+                    let fs_path = directory_fs_path.join(get_path_from_bytes(
+                        dirstate_node.base_name(self.dmap.on_disk)?.as_bytes(),
+                    ));
+                    match std::fs::symlink_metadata(&fs_path) {
+                        Ok(fs_metadata) => self.traverse_fs_and_dirstate(
+                            &fs_path,
+                            &fs_metadata,
+                            dirstate_node,
+                            has_ignored_ancestor,
+                        ),
+                        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
+                            self.traverse_dirstate_only(dirstate_node)
+                        }
+                        Err(error) => {
+                            let hg_path =
+                                dirstate_node.full_path(self.dmap.on_disk)?;
+                            Ok(self.io_error(error, hg_path))
+                        }
+                    }
+                })
+                .collect();
+        }
+
         let mut fs_entries = if let Ok(entries) = self.read_dir(
             directory_hg_path,
             directory_fs_path,
             is_at_repo_root,
         ) {
             entries
         } else {
             return Ok(());
         };
 
         // `merge_join_by` requires both its input iterators to be sorted:
 
         let dirstate_nodes = dirstate_nodes.sorted();
         // `sort_unstable_by_key` doesn’t allow keys borrowing from the value:
         // https://github.com/rust-lang/rust/issues/34162
         fs_entries.sort_unstable_by(|e1, e2| e1.base_name.cmp(&e2.base_name));
 
         // Propagate here any error that would happen inside the comparison
         // callback below
         for dirstate_node in &dirstate_nodes {
             dirstate_node.base_name(self.dmap.on_disk)?;
         }
         itertools::merge_join_by(
             dirstate_nodes,
             &fs_entries,
             |dirstate_node, fs_entry| {
                 // This `unwrap` never panics because we already propagated
                 // those errors above
                 dirstate_node
                     .base_name(self.dmap.on_disk)
                     .unwrap()
                     .cmp(&fs_entry.base_name)
             },
         )
         .par_bridge()
         .map(|pair| {
             use itertools::EitherOrBoth::*;
             match pair {
                 Both(dirstate_node, fs_entry) => self
                     .traverse_fs_and_dirstate(
-                        fs_entry,
+                        &fs_entry.full_path,
+                        &fs_entry.metadata,
                         dirstate_node,
                         has_ignored_ancestor,
                     ),
                 Left(dirstate_node) => {
                     self.traverse_dirstate_only(dirstate_node)
                 }
                 Right(fs_entry) => Ok(self.traverse_fs_only(
                     has_ignored_ancestor,
                     directory_hg_path,
                     fs_entry,
                 )),
             }
         })
         .collect()
     }
 
     fn traverse_fs_and_dirstate(
         &self,
-        fs_entry: &DirEntry,
+        fs_path: &Path,
+        fs_metadata: &std::fs::Metadata,
         dirstate_node: NodeRef<'tree, '_>,
         has_ignored_ancestor: bool,
     ) -> Result<(), DirstateV2ParseError> {
         let hg_path = dirstate_node.full_path(self.dmap.on_disk)?;
-        let file_type = fs_entry.metadata.file_type();
+        let file_type = fs_metadata.file_type();
         let file_or_symlink = file_type.is_file() || file_type.is_symlink();
         if !file_or_symlink {
             // If we previously had a file here, it was removed (with
             // `hg rm` or similar) or deleted before it could be
             // replaced by a directory or something else.
             self.mark_removed_or_deleted_if_file(
                 hg_path,
                 dirstate_node.state()?,
             );
         }
         if file_type.is_dir() {
             if self.options.collect_traversed_dirs {
                 self.outcome.lock().unwrap().traversed.push(hg_path.into())
             }
             let is_ignored = has_ignored_ancestor || (self.ignore_fn)(hg_path);
             let is_at_repo_root = false;
             self.traverse_fs_directory_and_dirstate(
                 is_ignored,
                 dirstate_node.children(self.dmap.on_disk)?,
                 hg_path,
-                &fs_entry.full_path,
+                fs_path,
                 is_at_repo_root,
             )?
         } else {
             if file_or_symlink && self.matcher.matches(hg_path) {
                 let full_path = Cow::from(hg_path);
                 if let Some(state) = dirstate_node.state()? {
                     match state {
                         EntryState::Added => {
                             self.outcome.lock().unwrap().added.push(full_path)
                         }
                         EntryState::Removed => self
                             .outcome
                             .lock()
                             .unwrap()
                             .removed
                             .push(full_path),
                         EntryState::Merged => self
                             .outcome
                             .lock()
                             .unwrap()
                             .modified
                             .push(full_path),
-                        EntryState::Normal => {
-                            self.handle_normal_file(&dirstate_node, fs_entry)?
-                        }
+                        EntryState::Normal => self
+                            .handle_normal_file(&dirstate_node, fs_metadata)?,
                         // This variant is not used in DirstateMap
                         // nodes
                         EntryState::Unknown => unreachable!(),
                     }
                 } else {
                     // `node.entry.is_none()` indicates a "directory"
                     // node, but the filesystem has a file
                     self.mark_unknown_or_ignored(
                         has_ignored_ancestor,
                         full_path,
                     )
                 }
             }
 
             for child_node in dirstate_node.children(self.dmap.on_disk)?.iter()
             {
                 self.traverse_dirstate_only(child_node)?
             }
         }
         Ok(())
     }
 
     /// A file with `EntryState::Normal` in the dirstate was found in the
     /// filesystem
     fn handle_normal_file(
         &self,
         dirstate_node: &NodeRef<'tree, '_>,
-        fs_entry: &DirEntry,
+        fs_metadata: &std::fs::Metadata,
     ) -> Result<(), DirstateV2ParseError> {
         // Keep the low 31 bits
         fn truncate_u64(value: u64) -> i32 {
             (value & 0x7FFF_FFFF) as i32
         }
         fn truncate_i64(value: i64) -> i32 {
             (value & 0x7FFF_FFFF) as i32
         }
 
         let entry = dirstate_node
             .entry()?
             .expect("handle_normal_file called with entry-less node");
         let full_path = Cow::from(dirstate_node.full_path(self.dmap.on_disk)?);
-        let mode_changed = || {
-            self.options.check_exec && entry.mode_changed(&fs_entry.metadata)
-        };
-        let size_changed = entry.size != truncate_u64(fs_entry.metadata.len());
+        let mode_changed =
+            || self.options.check_exec && entry.mode_changed(fs_metadata);
+        let size_changed = entry.size != truncate_u64(fs_metadata.len());
         if entry.size >= 0
             && size_changed
-            && fs_entry.metadata.file_type().is_symlink()
+            && fs_metadata.file_type().is_symlink()
         {
             // issue6456: Size returned may be longer due to encryption
             // on EXT-4 fscrypt. TODO maybe only do it on EXT4?
             self.outcome.lock().unwrap().unsure.push(full_path)
         } else if dirstate_node.has_copy_source()
             || entry.is_from_other_parent()
             || (entry.size >= 0 && (size_changed || mode_changed()))
         {
             self.outcome.lock().unwrap().modified.push(full_path)
         } else {
-            let mtime = mtime_seconds(&fs_entry.metadata);
+            let mtime = mtime_seconds(fs_metadata);
             if truncate_i64(mtime) != entry.mtime
                 || mtime == self.options.last_normal_time
             {
                 self.outcome.lock().unwrap().unsure.push(full_path)
             } else if self.options.list_clean {
                 self.outcome.lock().unwrap().clean.push(full_path)
             }
         }
         Ok(())
     }
 
     /// A node in the dirstate tree has no corresponding filesystem entry
     fn traverse_dirstate_only(
         &self,
         dirstate_node: NodeRef<'tree, '_>,
     ) -> Result<(), DirstateV2ParseError> {
         self.mark_removed_or_deleted_if_file(
             dirstate_node.full_path(self.dmap.on_disk)?,
             dirstate_node.state()?,
         );
         dirstate_node
             .children(self.dmap.on_disk)?
             .par_iter()
             .map(|child_node| self.traverse_dirstate_only(child_node))
             .collect()
     }
 
     /// A node in the dirstate tree has no corresponding *file* on the
     /// filesystem
     ///
     /// Does nothing on a "directory" node
     fn mark_removed_or_deleted_if_file(
         &self,
         hg_path: &'tree HgPath,
         dirstate_node_state: Option<EntryState>,
     ) {
         if let Some(state) = dirstate_node_state {
             if self.matcher.matches(hg_path) {
                 if let EntryState::Removed = state {
                     self.outcome.lock().unwrap().removed.push(hg_path.into())
                 } else {
                     self.outcome.lock().unwrap().deleted.push(hg_path.into())
                 }
             }
         }
     }
 
     /// Something in the filesystem has no corresponding dirstate node
     fn traverse_fs_only(
         &self,
         has_ignored_ancestor: bool,
         directory_hg_path: &HgPath,
         fs_entry: &DirEntry,
     ) {
         let hg_path = directory_hg_path.join(&fs_entry.base_name);
         let file_type = fs_entry.metadata.file_type();
         let file_or_symlink = file_type.is_file() || file_type.is_symlink();
         if file_type.is_dir() {
             let is_ignored =
                 has_ignored_ancestor || (self.ignore_fn)(&hg_path);
             let traverse_children = if is_ignored {
                 // Descendants of an ignored directory are all ignored
                 self.options.list_ignored
             } else {
                 // Descendants of an unknown directory may be either unknown or
                 // ignored
                 self.options.list_unknown || self.options.list_ignored
             };
             if traverse_children {
                 let is_at_repo_root = false;
                 if let Ok(children_fs_entries) = self.read_dir(
                     &hg_path,
                     &fs_entry.full_path,
                     is_at_repo_root,
                 ) {
                     children_fs_entries.par_iter().for_each(|child_fs_entry| {
                         self.traverse_fs_only(
                             is_ignored,
                             &hg_path,
                             child_fs_entry,
                         )
                     })
                 }
             }
             if self.options.collect_traversed_dirs {
                 self.outcome.lock().unwrap().traversed.push(hg_path.into())
             }
         } else if file_or_symlink && self.matcher.matches(&hg_path) {
             self.mark_unknown_or_ignored(has_ignored_ancestor, hg_path.into())
         }
     }
 
     fn mark_unknown_or_ignored(
         &self,
         has_ignored_ancestor: bool,
         hg_path: Cow<'tree, HgPath>,
     ) {
         let is_ignored = has_ignored_ancestor || (self.ignore_fn)(&hg_path);
         if is_ignored {
             if self.options.list_ignored {
                 self.outcome.lock().unwrap().ignored.push(hg_path)
             }
         } else {
             if self.options.list_unknown {
                 self.outcome.lock().unwrap().unknown.push(hg_path)
             }
         }
     }
 }
 
 #[cfg(unix)] // TODO
 fn mtime_seconds(metadata: &std::fs::Metadata) -> i64 {
     // Going through `Metadata::modified()` would be portable, but would take
     // care to construct a `SystemTime` value with sub-second precision just
     // for us to throw that away here.
     use std::os::unix::fs::MetadataExt;
     metadata.mtime()
 }
 
 struct DirEntry {
     base_name: HgPathBuf,
     full_path: PathBuf,
     metadata: std::fs::Metadata,
 }
 
 impl DirEntry {
     /// Returns **unsorted** entries in the given directory, with name and
     /// metadata.
     ///
     /// If a `.hg` sub-directory is encountered:
     ///
     /// * 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)
     }
 }