This patch is work based on the following 2 commits:
Linus Torvalds: c40641b77b0274186fd1b327d5dc3246f814aaaf
Junio C Hamano: f859c846e90b385c7ef873df22403529208ade50
Changes includes the following:
- The cache functionality is more effective. Previously when A/B/C/D
was in the cache and A/B/C/E/file.c was called for, there was no
match at all from the cache. Now we use the fact that the paths
"A", "A/B" and "A/B/C" is already tested, and we only need to do an
lstat() call on "A/B/C/E".
- We only cache/store the last path regardless of it's type. Since the
cache functionality is always used with alphabetically sorted names
(at least it seams so for me), there is no need to store both the
last symlink-leading path and the last real-directory path. Note
that if the cache is not called with (mostly) alphabetically sorted
names, neither the old, nor this new one, would be very effective.
- We also can cache the fact that a directory does not exist.
Previously we could end up doing lots of lstat() calls for a removed
directory which previously contained lots of files. Since we
already have simplified the cache functionality and only store the
last path (see above), this new functionality was easy to add.
- Previously, when symlink A/B/C/S was cached/stored in the
symlink-leading path, and A/B/C/file.c was called for, it was not
easy to use the fact that we already known that the paths "A", "A/B"
and "A/B/C" is real directories. Since we now only store one single
path (the last one), we also get similar logic for free regarding
the new "non-exsisting-directory-cache".
- Avoid copying the first path components of the name 2 zillions times
when we tests new path components. Since we always cache/store the
last path, we can copy each component as we test those directly into
the cache. Previously we ended up doing a memcpy() for the full
path/name right before each lstat() call, and when updating the
cache for each time we have tested an new path component.
- We also use less memory, that is PATH_MAX bytes less memory on the
stack and PATH_MAX bytes less memory on the heap.
- Introduce a 3rd argument, 'unsigned int track_flags', to the
cache-test function, check_lstat_cache(). This new argument can be
used to tell the cache functionality which types of directories
should be cached.
- Also introduce a 'void clear_lstat_cache(void)' function, which
should be used to clean the cache before usage. If for instance,
you have changed the types of directories which should be cached,
the cache could contain a path which was not wanted.
Signed-off-by: Kjetil Barvik <barvik@xxxxxxxxxxxx>
---
:100644 100644 aabf013... 7449b10... M Makefile
:100644 100644 231c06d... 9adc4a2... M cache.h
:000000 100644 0000000... 2f025c8... A lstat_cache.c
Makefile | 1 +
cache.h | 15 +++++++++
lstat_cache.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 115 insertions(+), 0 deletions(-)
create mode 100644 lstat_cache.c
diff --git a/Makefile b/Makefile
index aabf0130b99bee5204c8e668ba8f40caea77dae2..7449b105b03e862d53244d50ed035b4ddabef028 100644
--- a/Makefile
+++ b/Makefile
@@ -446,6 +446,7 @@ LIB_OBJS += list-objects.o
LIB_OBJS += ll-merge.o
LIB_OBJS += lockfile.o
LIB_OBJS += log-tree.o
+LIB_OBJS += lstat_cache.o
LIB_OBJS += mailmap.o
LIB_OBJS += match-trees.o
LIB_OBJS += merge-file.o
diff --git a/cache.h b/cache.h
index 231c06d7726b575f6e522d5b0c0fe43557e8c651..9adc4a224648bb17a50e6792274225eeb6144451 100644
--- a/cache.h
+++ b/cache.h
@@ -721,6 +721,21 @@ struct checkout {
extern int checkout_entry(struct cache_entry *ce, const struct checkout *state, char *topath);
extern int has_symlink_leading_path(int len, const char *name);
+#define LSTAT_DIR (1u << 0)
+#define LSTAT_NOENT (1u << 1)
+#define LSTAT_SYMLINK (1u << 2)
+#define LSTAT_LSTATERR (1u << 3)
+#define LSTAT_ERR (1u << 4)
+extern unsigned int check_lstat_cache(int len, const char *name,
+ unsigned int track_flags);
+static inline unsigned int lstat_cache(int len, const char *name,
+ unsigned int track_flags,
+ unsigned int mask_flags)
+{
+ return check_lstat_cache(len, name, track_flags) & mask_flags;
+}
+extern void clear_lstat_cache(void);
+
extern struct alternate_object_database {
struct alternate_object_database *next;
char *name;
diff --git a/lstat_cache.c b/lstat_cache.c
new file mode 100644
index 0000000000000000000000000000000000000000..2f025c87b0be0e713af7b1400e71284a22c25e9f
--- /dev/null
+++ b/lstat_cache.c
@@ -0,0 +1,99 @@
+#include "cache.h"
+
+static char cache_path[PATH_MAX];
+static int cache_len = 0;
+static unsigned int cache_flags = 0;
+
+static inline int
+greatest_common_path_cache_prefix(int len, const char *name)
+{
+ int max_len, match_len = 0, i = 0;
+
+ max_len = len < cache_len ? len : cache_len;
+ while (i < max_len && name[i] == cache_path[i]) {
+ if (name[i] == '/') match_len = i;
+ i++;
+ }
+ if (i == cache_len && len > cache_len && name[cache_len] == '/')
+ match_len = cache_len;
+ return match_len;
+}
+
+/*
+ * Check if name 'name' of length 'len' has a symlink leading
+ * component, or if the directory exists and is real, or not.
+ *
+ * To speed up the check, some information is allowed to be cached.
+ * This is indicated by the 'track_flags' argument.
+ */
+unsigned int
+check_lstat_cache(int len, const char *name, unsigned int track_flags)
+{
+ int match_len, last_slash, max_len;
+ unsigned int match_flags, ret_flags, save_flags;
+ struct stat st;
+
+ /* Check if match from the cache for 2 "excluding" path types.
+ */
+ match_len = last_slash =
+ greatest_common_path_cache_prefix(len, name);
+ match_flags =
+ cache_flags & track_flags & (LSTAT_NOENT|LSTAT_SYMLINK);
+ if (match_flags && match_len == cache_len)
+ return match_flags;
+
+ /* Okay, no match from the cache so far, so now we have to
+ * check the rest of the path components.
+ */
+ ret_flags = LSTAT_DIR;
+ max_len = len < PATH_MAX ? len : PATH_MAX;
+ while (match_len < max_len) {
+ do {
+ cache_path[match_len] = name[match_len];
+ match_len++;
+ } while (match_len < max_len && name[match_len] != '/');
+ if (match_len >= max_len)
+ break;
+ last_slash = match_len;
+ cache_path[last_slash] = '\0';
+
+ if (lstat(cache_path, &st)) {
+ ret_flags = LSTAT_LSTATERR;
+ if (errno == ENOENT)
+ ret_flags |= LSTAT_NOENT;
+ } else if (S_ISDIR(st.st_mode)) {
+ continue;
+ } else if (S_ISLNK(st.st_mode)) {
+ ret_flags = LSTAT_SYMLINK;
+ } else {
+ ret_flags = LSTAT_ERR;
+ }
+ break;
+ }
+
+ /* At the end update the cache. Note that max 3 different
+ * path types can be cached for the moment!
+ */
+ save_flags = ret_flags & track_flags &
+ (LSTAT_NOENT|LSTAT_SYMLINK|LSTAT_DIR);
+ if (save_flags && last_slash > 0 && last_slash < PATH_MAX) {
+ cache_path[last_slash] = '\0';
+ cache_len = last_slash;
+ cache_flags = save_flags;
+ } else {
+ clear_lstat_cache();
+ }
+ return ret_flags;
+}
+
+/*
+ * Before usage of the check_lstat_cache() function one should call
+ * clear_lstat_cache() (at an appropriate place) to make sure that the
+ * cache is clean.
+ */
+void clear_lstat_cache(void)
+{
+ cache_path[0] = '\0';
+ cache_len = 0;
+ cache_flags = 0;
+}
--
1.6.1.rc1.49.g7f705
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
