Re: [PATCH v3 2/3] dir: cache git_dir's realpath
From: Elijah Newren <hidden>
Date: 2022-05-24 14:32:58
On Fri, May 20, 2022 at 12:29 PM Goss Geppert [off-list ref] wrote:
quoted hunk ↗ jump to hunk
When traversing the directory tree, the realpath of the `git_dir` is required each time a nested repository is encountered to determine how the nested repository should be treated. To prevent excessive resource usage in pathological cases (e.g. many nested repositories, a long path, symlinks, etc.), cache the realpath after the first usage until the traversal is complete. --- dir.c | 63 ++++++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 43 insertions(+), 20 deletions(-)diff --git a/dir.c b/dir.c index e45e117875..45b89560fc 100644 --- a/dir.c +++ b/dir.c@@ -47,10 +47,22 @@ struct cached_dir { struct untracked_cache_dir *ucd; }; +/* + * Support data structure for the recursing into the directory tree. + */ +struct traversal_cache { + /* + * The realpath for the `git_dir` may be required in the recursion and is + * cached for repeated use. + */ + char *real_gitdir; +}; + static enum path_treatment read_directory_recursive(struct dir_struct *dir, struct index_state *istate, const char *path, int len, struct untracked_cache_dir *untracked, - int check_only, int stop_at_first_file, const struct pathspec *pathspec); + int check_only, int stop_at_first_file, const struct pathspec *pathspec, + struct traversal_cache *cache); static int resolve_dtype(int dtype, struct index_state *istate, const char *path, int len); struct dirent *readdir_skip_dot_and_dotdot(DIR *dirp)@@ -1852,7 +1864,8 @@ static enum path_treatment treat_directory(struct dir_struct *dir, struct index_state *istate, struct untracked_cache_dir *untracked, const char *dirname, int len, int baselen, int excluded, - const struct pathspec *pathspec) + const struct pathspec *pathspec, + struct traversal_cache *cache) { /* * WARNING: From this function, you can return path_recurse or you@@ -1906,13 +1919,13 @@ static enum path_treatment treat_directory(struct dir_struct *dir, nested_repo = is_nonbare_repository_dir(&sb); if (nested_repo) { - char *real_dirname, *real_gitdir; + char *real_dirname; strbuf_addstr(&sb, ".git"); real_dirname = real_pathdup(sb.buf, 1); - real_gitdir = real_pathdup(the_repository->gitdir, 1); + if (!cache->real_gitdir) + cache->real_gitdir = real_pathdup(the_repository->gitdir, 1); - nested_repo = !!strcmp(real_dirname, real_gitdir); - free(real_gitdir); + nested_repo = !!strcmp(real_dirname, cache->real_gitdir); free(real_dirname); } strbuf_release(&sb);@@ -1944,7 +1957,7 @@ static enum path_treatment treat_directory(struct dir_struct *dir, return path_excluded; if (read_directory_recursive(dir, istate, dirname, len, - untracked, 1, 1, pathspec) == path_excluded) + untracked, 1, 1, pathspec, cache) == path_excluded) return path_excluded; return path_none;@@ -2045,7 +2058,7 @@ static enum path_treatment treat_directory(struct dir_struct *dir, untracked = lookup_untracked(dir->untracked, untracked, dirname + baselen, len - baselen); state = read_directory_recursive(dir, istate, dirname, len, untracked, - check_only, stop_early, pathspec); + check_only, stop_early, pathspec, cache); /* There are a variety of reasons we may need to fixup the state... */ if (state == path_excluded) {@@ -2242,7 +2255,8 @@ static enum path_treatment treat_path_fast(struct dir_struct *dir, struct index_state *istate, struct strbuf *path, int baselen, - const struct pathspec *pathspec) + const struct pathspec *pathspec, + struct traversal_cache *cache) { /* * WARNING: From this function, you can return path_recurse or you@@ -2264,7 +2278,7 @@ static enum path_treatment treat_path_fast(struct dir_struct *dir, * with check_only set. */ return read_directory_recursive(dir, istate, path->buf, path->len, - cdir->ucd, 1, 0, pathspec); + cdir->ucd, 1, 0, pathspec, cache); /* * We get path_recurse in the first run when * directory_exists_in_index() returns index_nonexistent. We@@ -2280,13 +2294,14 @@ static enum path_treatment treat_path(struct dir_struct *dir, struct index_state *istate, struct strbuf *path, int baselen, - const struct pathspec *pathspec) + const struct pathspec *pathspec, + struct traversal_cache *cache) { int has_path_in_index, dtype, excluded; if (!cdir->d_name) return treat_path_fast(dir, cdir, istate, path, - baselen, pathspec); + baselen, pathspec, cache); if (is_dot_or_dotdot(cdir->d_name) || !fspathcmp(cdir->d_name, ".git")) return path_none; strbuf_setlen(path, baselen);@@ -2348,7 +2363,7 @@ static enum path_treatment treat_path(struct dir_struct *dir, strbuf_addch(path, '/'); return treat_directory(dir, istate, untracked, path->buf, path->len, - baselen, excluded, pathspec); + baselen, excluded, pathspec, cache); case DT_REG: case DT_LNK: if (pathspec &&@@ -2549,7 +2564,8 @@ static void add_path_to_appropriate_result_list(struct dir_struct *dir, static enum path_treatment read_directory_recursive(struct dir_struct *dir, struct index_state *istate, const char *base, int baselen, struct untracked_cache_dir *untracked, int check_only, - int stop_at_first_file, const struct pathspec *pathspec) + int stop_at_first_file, const struct pathspec *pathspec, + struct traversal_cache *cache) { /* * WARNING: Do NOT recurse unless path_recurse is returned from@@ -2572,7 +2588,7 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir, while (!read_cached_dir(&cdir)) { /* check how the file or directory should be treated */ state = treat_path(dir, untracked, &cdir, istate, &path, - baselen, pathspec); + baselen, pathspec, cache); dir->visited_paths++; if (state > dir_state)@@ -2587,7 +2603,7 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir, subdir_state = read_directory_recursive(dir, istate, path.buf, path.len, ud, - check_only, stop_at_first_file, pathspec); + check_only, stop_at_first_file, pathspec, cache); if (subdir_state > dir_state) dir_state = subdir_state;@@ -2661,7 +2677,8 @@ int check_dir_entry_contains(const struct dir_entry *out, const struct dir_entry static int treat_leading_path(struct dir_struct *dir, struct index_state *istate, const char *path, int len, - const struct pathspec *pathspec) + const struct pathspec *pathspec, + struct traversal_cache *cache) { struct strbuf sb = STRBUF_INIT; struct strbuf subdir = STRBUF_INIT;@@ -2713,7 +2730,8 @@ static int treat_leading_path(struct dir_struct *dir, strbuf_reset(&subdir); strbuf_add(&subdir, path+prevlen, baselen-prevlen); cdir.d_name = subdir.buf; - state = treat_path(dir, NULL, &cdir, istate, &sb, prevlen, pathspec); + + state = treat_path(dir, NULL, &cdir, istate, &sb, prevlen, pathspec, cache); if (state != path_recurse) break; /* do not recurse into it */@@ -2986,6 +3004,9 @@ int read_directory(struct dir_struct *dir, struct index_state *istate, const char *path, int len, const struct pathspec *pathspec) { struct untracked_cache_dir *untracked; + struct traversal_cache cache = { + .real_gitdir = NULL, + }; trace2_region_enter("dir", "read_directory", istate->repo); dir->visited_paths = 0;@@ -3003,8 +3024,10 @@ int read_directory(struct dir_struct *dir, struct index_state *istate, * e.g. prep_exclude() */ dir->untracked = NULL; - if (!len || treat_leading_path(dir, istate, path, len, pathspec)) - read_directory_recursive(dir, istate, path, len, untracked, 0, 0, pathspec); + if (!len || treat_leading_path(dir, istate, path, len, pathspec, &cache)) { + read_directory_recursive(dir, istate, path, len, untracked, 0, 0, pathspec, &cache); + } + FREE_AND_NULL(cache.real_gitdir); QSORT(dir->entries, dir->nr, cmp_dir_entry); QSORT(dir->ignored, dir->ignored_nr, cmp_dir_entry); --2.36.0
This makes sense as a way to avoid the call to real_pathdup() if that's what we want, but I feel it's a micro-optimization that isn't worth this code churn. I'd rather drop this patch from the series and just use the real_pathdup() you had before (see https://lore.kernel.org/git/CABPp-BGXRzYCvyM38dEUvQ125+VtRu++7L9UiRz98u+1=Lov7A@mail.gmail.com/ (local)). Let's see what Junio says, but I'm hoping he agrees this patch isn't needed.