Speed up reflog pruning of unreachable commits

Instead of doing the (potentially very expensive) "in_merge_base()"
check for each commit that might be pruned if it is unreachable, do a
preparatory reachability graph of the commit space, so that the common
case of being reachable can be tested directly.

[ Cleaned up a bit and tweaked to actually work.  - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-reflog.c b/builtin-reflog.c
index a07960ff5e395b9e4fdd9816daf4da06b89162e2..249ad2a311f2e9680618870aed3ac053c9fcf7a1 100644 (file)
--- a/builtin-reflog.c
+++ b/builtin-reflog.c
@@ -52,6 +52,7 @@ struct collect_reflog_cb {
 
 #define INCOMPLETE     (1u<<10)
 #define STUDYING       (1u<<11)
+#define REACHABLE      (1u<<12)
 
 static int tree_is_complete(const unsigned char *sha1)
 {
@@ -227,6 +228,8 @@ static int unreachable(struct expire_reflog_cb *cb, struct commit *commit, unsig
        }
 
        /* Reachable from the current ref?  Don't prune. */
+       if (commit->object.flags & REACHABLE)
+               return 0;
        if (in_merge_bases(commit, &cb->ref_commit, 1))
                return 0;
 
@@ -234,6 +237,43 @@ static int unreachable(struct expire_reflog_cb *cb, struct commit *commit, unsig
        return 1;
 }
 
+static void mark_reachable(struct commit *commit, unsigned long expire_limit)
+{
+       /*
+        * We need to compute if commit on either side of an reflog
+        * entry is reachable from the tip of the ref for all entries.
+        * Mark commits that are reachable from the tip down to the
+        * time threashold first; we know a commit marked thusly is
+        * reachable from the tip without running in_merge_bases()
+        * at all.
+        */
+       struct commit_list *pending = NULL;
+
+       commit_list_insert(commit, &pending);
+       while (pending) {
+               struct commit_list *entry = pending;
+               struct commit_list *parent;
+               pending = entry->next;
+               commit = entry->item;
+               free(entry);
+               if (commit->object.flags & REACHABLE)
+                       continue;
+               if (parse_commit(commit))
+                       continue;
+               commit->object.flags |= REACHABLE;
+               if (commit->date < expire_limit)
+                       continue;
+               parent = commit->parents;
+               while (parent) {
+                       commit = parent->item;
+                       parent = parent->next;
+                       if (commit->object.flags & REACHABLE)
+                               continue;
+                       commit_list_insert(commit, &pending);
+               }
+       }
+}
+
 static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
                const char *email, unsigned long timestamp, int tz,
                const char *message, void *cb_data)
@@ -308,7 +348,11 @@ static int expire_reflog(const char *ref, const unsigned char *sha1, int unused,
        cb.ref_commit = lookup_commit_reference_gently(sha1, 1);
        cb.ref = ref;
        cb.cmd = cmd;
+       if (cb.ref_commit)
+               mark_reachable(cb.ref_commit, cmd->expire_total);
        for_each_reflog_ent(ref, expire_reflog_ent, &cb);
+       if (cb.ref_commit)
+               clear_commit_marks(cb.ref_commit, REACHABLE);
  finish:
        if (cb.newlog) {
                if (fclose(cb.newlog)) {