Avoid accessing a slow working copy during diffcore operations.

diff --git a/diff.c b/diff.c
index 2df14b2469362bfd8a30a45457953d993baae66d..77ba641aa48974a7601875bd0a6a351baa30e726 100644 (file)
--- a/diff.c
+++ b/diff.c
@@ -12,6 +12,12 @@
 #include "xdiff-interface.h"
 #include "color.h"
 
+#ifdef NO_FAST_WORKING_DIRECTORY
+#define FAST_WORKING_DIRECTORY 0
+#else
+#define FAST_WORKING_DIRECTORY 1
+#endif
+
 static int use_size_cache;
 
 static int diff_detect_rename_default;
@@ -1158,7 +1164,7 @@ void fill_filespec(struct diff_filespec *spec, const unsigned char *sha1,
  * the work tree has that object contents, return true, so that
  * prepare_temp_file() does not have to inflate and extract.
  */
-static int work_tree_matches(const char *name, const unsigned char *sha1)
+static int reuse_worktree_file(const char *name, const unsigned char *sha1, int want_file)
 {
        struct cache_entry *ce;
        struct stat st;
@@ -1179,6 +1185,18 @@ static int work_tree_matches(const char *name, const unsigned char *sha1)
        if (!active_cache)
                return 0;
 
+       /* We want to avoid the working directory if our caller
+        * doesn't need the data in a normal file, this system
+        * is rather slow with its stat/open/mmap/close syscalls,
+        * and the object is contained in a pack file.  The pack
+        * is probably already open and will be faster to obtain
+        * the data through than the working directory.  Loose
+        * objects however would tend to be slower as they need
+        * to be individually opened and inflated.
+        */
+       if (FAST_WORKING_DIRECTORY && !want_file && has_sha1_pack(sha1, NULL))
+               return 0;
+
        len = strlen(name);
        pos = cache_name_pos(name, len);
        if (pos < 0)
@@ -1265,7 +1283,7 @@ int diff_populate_filespec(struct diff_filespec *s, int size_only)
        if (s->data)
                return err;
        if (!s->sha1_valid ||
-           work_tree_matches(s->path, s->sha1)) {
+           reuse_worktree_file(s->path, s->sha1, 0)) {
                struct stat st;
                int fd;
                if (lstat(s->path, &st) < 0) {
@@ -1372,7 +1390,7 @@ static void prepare_temp_file(const char *name,
        }
 
        if (!one->sha1_valid ||
-           work_tree_matches(name, one->sha1)) {
+           reuse_worktree_file(name, one->sha1, 1)) {
                struct stat st;
                if (lstat(name, &st) < 0) {
                        if (errno == ENOENT)