Commit Diff

Commit:
70f8f24dc5b689abd6265a71e787dfef79ba40cf
From:
Stefan Sperling <stsp@stsp.name>
Date:
Message:
speed up initial stage of packing by adding a "skip" commit color The skip color marks boundary commits and their ancestors. Boundary commits are reachable both via references which we want to exclude from the pack, and via references which we want to include in the pack. We continue processing commit history up to the point we are left with only skip commits on the queue. This can speed up findtwixt() significantly and avoids wrong results produced by the old algorithm which made no distinction between "drop" and "skip". This idea was first implemented by Michael Forney for git9: https://git.9front.org/plan9front/plan9front/2e47badb88312c5c045a8042dc2ef80148e5ab47/commit.html Michael's log message for git9 is reproduced below: git/query: refactor graph painting algorithm (findtwixt, lca) We now keep track of 3 sets during traversal: - keep: commits we've reached from head commits - drop: commits we've reached from tail commits - skip: ancestors of commits in both 'keep' and 'drop' Commits in 'keep' and/or 'drop' may be added later to the 'skip' set if we discover later that they are part of a common subgraph of the head and tail commits. From these sets we can calculate the commits we are interested in: lca commits are those in 'keep' and 'drop', but not in 'skip'. findtwixt commits are those in 'keep', but not in 'drop' or 'skip'. The "LCA" commit returned is a common ancestor such that there are no other common ancestors that can reach that commit. Although there can be multiple commits that meet this criteria, where one is technically lower on the commit-graph than the other, these cases only happen in complex merge arrangements and any choice is likely a decent merge base. Repainting is now done in paint() directly. When we find a boundary commit, we switch our paint color to 'skip'. 'skip' painting does not stop when it hits another color; we continue until we are left with only 'skip' commits on the queue. This fixes several mishandled cases in the current algorithm: 1. If we hit the common subgraph from tail commits first (if the tail commit was newer than the head commit), we ended up traversing the entire commit graph. This is because we couldn't distinguish between 'drop' commits that were part of the common subgraph, and those that were still looking for it. 2. If we traversed through an initial part of the common subgraph from head commits before reaching it from tail commits, these commits were returned from findtwixt even though they were also reachable from tail commits. 3. In the same case as 2, we might end up choosing an incorrect commit as the LCA, which is an ancestor of the real LCA.
Actions:
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commit - a7472cb3288c2323830462f53706b013f33c444e
commit + 70f8f24dc5b689abd6265a71e787dfef79ba40cf
blob - 4e9a9b9541862d224810bd98f0fb1953d78d7259
blob + fa7ea77d02fc1d6284318e12d67fc4c0742fde70
--- lib/pack_create.c
+++ lib/pack_create.c
@@ -61,6 +61,10 @@
 #define	MAX(_a,_b) ((_a) > (_b) ? (_a) : (_b))
 #endif
 
+#ifndef nitems
+#define nitems(_a)	(sizeof((_a)) / sizeof((_a)[0]))
+#endif
+
 struct got_pack_meta {
 	struct got_object_id id;
 	char	*path;
@@ -1108,96 +1112,46 @@ enum findtwixt_color {
 	COLOR_KEEP = 0,
 	COLOR_DROP,
 	COLOR_BLANK,
+	COLOR_SKIP,
 };
+
 static const int findtwixt_colors[] = {
 	COLOR_KEEP,
 	COLOR_DROP,
-	COLOR_BLANK
+	COLOR_BLANK,
+	COLOR_SKIP,
 };
 
 static const struct got_error *
-queue_commit_id(struct got_object_id_queue *ids, struct got_object_id *id,
-    int color, struct got_repository *repo)
+paint_commit(struct got_object_qid *qid, int color)
 {
-	const struct got_error *err;
-	struct got_object_qid *qid;
-
-	err = got_object_qid_alloc(&qid, id);
-	if (err)
-		return err;
+	if (color < 0 || color >= nitems(findtwixt_colors))
+		return got_error(GOT_ERR_RANGE);
 
-	STAILQ_INSERT_TAIL(ids, qid, entry);
 	qid->data = (void *)&findtwixt_colors[color];
 	return NULL;
 }
 
 static const struct got_error *
-drop_commit(struct got_object_idset *keep, struct got_object_idset *drop,
-    struct got_object_id *id, struct got_repository *repo,
-    got_cancel_cb cancel_cb, void *cancel_arg)
+queue_commit_id(struct got_object_id_queue *ids, struct got_object_id *id,
+    int color, struct got_repository *repo)
 {
-	const struct got_error *err = NULL;
-	struct got_commit_object *commit;
-	const struct got_object_id_queue *parents;
-	struct got_object_id_queue ids;
+	const struct got_error *err;
 	struct got_object_qid *qid;
 
-	STAILQ_INIT(&ids);
-
 	err = got_object_qid_alloc(&qid, id);
 	if (err)
 		return err;
-	STAILQ_INSERT_HEAD(&ids, qid, entry);
-
-	while (!STAILQ_EMPTY(&ids)) {
-		if (cancel_cb) {
-			err = (*cancel_cb)(cancel_arg);
-			if (err)
-				break;
-		}
-
-		qid = STAILQ_FIRST(&ids);
-		STAILQ_REMOVE_HEAD(&ids, entry);
-
-		if (got_object_idset_contains(drop, qid->id)) {
-			got_object_qid_free(qid);
-			continue;
-		}
-
-		err = got_object_idset_add(drop, qid->id, NULL);
-		if (err) {
-			got_object_qid_free(qid);
-			break;
-		}
-
-		if (!got_object_idset_contains(keep, qid->id)) {
-			got_object_qid_free(qid);
-			continue;
-		}
-
-		err = got_object_open_as_commit(&commit, repo, qid->id);
-		got_object_qid_free(qid);
-		if (err)
-			break;
 
-		parents = got_object_commit_get_parent_ids(commit);
-		if (parents) {
-			err = got_object_id_queue_copy(parents, &ids);
-			if (err) {
-				got_object_commit_close(commit);
-				break;
-			}
-		}
-		got_object_commit_close(commit);
-	}
-
-	got_object_id_queue_free(&ids);
-	return err;
+	STAILQ_INSERT_TAIL(ids, qid, entry);
+	return paint_commit(qid, color);
 }
 
 struct append_id_arg {
 	struct got_object_id **array;
 	int idx;
+	struct got_object_idset *drop;
+	struct got_object_idset *skip;
 };
 
 static const struct got_error *
@@ -1205,11 +1159,14 @@ append_id(struct got_object_id *id, void *data, void *
 {
 	struct append_id_arg *a = arg;
 
-	a->array[a->idx] = got_object_id_dup(id);
+	if (got_object_idset_contains(a->skip, id) ||
+	    got_object_idset_contains(a->drop, id))
+		return NULL;
+
+	a->array[++a->idx] = got_object_id_dup(id);
 	if (a->array[a->idx] == NULL)
 		return got_error_from_errno("got_object_id_dup");
 
-	a->idx++;
 	return NULL;
 }
 
@@ -1245,18 +1202,20 @@ done:
 }
 
 static const struct got_error *
-color_commits(int *ncolored, struct got_object_id_queue *ids,
+paint_commits(int *ncolored, struct got_object_id_queue *ids, int nids,
     struct got_object_idset *keep, struct got_object_idset *drop,
-    struct got_repository *repo,
+    struct got_object_idset *skip, struct got_repository *repo,
     got_pack_progress_cb progress_cb, void *progress_arg,
     struct got_ratelimit *rl, got_cancel_cb cancel_cb, void *cancel_arg)
 {
 	const struct got_error *err = NULL;
 	struct got_commit_object *commit = NULL;
+	const struct got_object_id_queue *parents;
 	struct got_object_qid *qid;
+	int nqueued = nids, nskip = 0;
 
-	while (!STAILQ_EMPTY(ids)) {
-		int qcolor, ncolor;
+	while (!STAILQ_EMPTY(ids) && nskip != nqueued) {
+		int color;
 
 		if (cancel_cb) {
 			err = cancel_cb(cancel_arg);
@@ -1265,71 +1224,94 @@ color_commits(int *ncolored, struct got_object_id_queu
 		}
 
 		qid = STAILQ_FIRST(ids);
-		qcolor = *((int *)qid->data);
+		STAILQ_REMOVE_HEAD(ids, entry);
+		nqueued--;
+		color = *((int *)qid->data);
+		if (color == COLOR_SKIP)
+			nskip--;
 
-		if (got_object_idset_contains(drop, qid->id))
-			ncolor = COLOR_DROP;
-		else if (got_object_idset_contains(keep, qid->id))
-			ncolor = COLOR_KEEP;
-		else
-			ncolor = COLOR_BLANK;
+		if (got_object_idset_contains(skip, qid->id)) {
+			got_object_qid_free(qid);
+			continue;
+		}
 
-		(*ncolored)++;
+		switch (color) {
+		case COLOR_KEEP:
+			if (got_object_idset_contains(keep, qid->id)) {
+				got_object_qid_free(qid);
+				continue;
+			}
+			if (got_object_idset_contains(drop, qid->id)) {
+				err = paint_commit(qid, COLOR_SKIP);
+				if (err)
+					goto done;
+				nskip++;
+			} else
+				(*ncolored)++;
+			err = got_object_idset_add(keep, qid->id, NULL);
+			if (err)
+				goto done;
+			break;
+		case COLOR_DROP:
+			if (got_object_idset_contains(drop, qid->id)) {
+				got_object_qid_free(qid);
+				continue;
+			}
+			if (got_object_idset_contains(keep, qid->id)) {
+				err = paint_commit(qid, COLOR_SKIP);
+				if (err)
+					goto done;
+				nskip++;
+			} else
+				(*ncolored)++;
+			err = got_object_idset_add(drop, qid->id, NULL);
+			if (err)
+				goto done;
+			break;
+		case COLOR_SKIP:
+			if (!got_object_idset_contains(skip, qid->id)) {
+				err = got_object_idset_add(skip, qid->id, NULL);
+				if (err)
+					goto done;
+			}
+			break;
+		default:
+			/* should not happen */
+			err = got_error_fmt(GOT_ERR_NOT_IMPL,
+			    "%s invalid commit color %d", __func__, color);
+			goto done;
+		}
+
 		err = report_progress(progress_cb, progress_arg, rl,
 		    *ncolored, 0, 0, 0L, 0, 0, 0, 0);
 		if (err)
 			break;
 
-		if (ncolor == COLOR_DROP || (ncolor == COLOR_KEEP &&
-		    qcolor == COLOR_KEEP)) {
-			STAILQ_REMOVE_HEAD(ids, entry);
-			got_object_qid_free(qid);
-			continue;
-		}
 
-		if (ncolor == COLOR_KEEP && qcolor == COLOR_DROP) {
-			err = drop_commit(keep, drop, qid->id, repo,
-			    cancel_cb, cancel_arg);
-			if (err)
-				break;
-		} else if (ncolor == COLOR_BLANK) {
-			struct got_commit_object *commit;
-			const struct got_object_id_queue *parents;
-			struct got_object_qid *pid;
-
-			if (qcolor == COLOR_KEEP)
-				err = got_object_idset_add(keep, qid->id, NULL);
-			else
-				err = got_object_idset_add(drop, qid->id, NULL);
-			if (err)
-				break;
+		err = got_object_open_as_commit(&commit, repo, qid->id);
+		if (err)
+			break;
 
-			err = got_object_open_as_commit(&commit, repo, qid->id);
-			if (err)
-				break;
-
-			parents = got_object_commit_get_parent_ids(commit);
-			if (parents) {
-				STAILQ_FOREACH(pid, parents, entry) {
-					err = queue_commit_id(ids, pid->id,
-					    qcolor, repo);
-					if (err)
-						break;
-				}
+		parents = got_object_commit_get_parent_ids(commit);
+		if (parents) {
+			struct got_object_qid *pid;
+			color = *((int *)qid->data);
+			STAILQ_FOREACH(pid, parents, entry) {
+				err = queue_commit_id(ids, pid->id, color,
+				    repo);
+				if (err)
+					break;
+				nqueued++;
+				if (color == COLOR_SKIP)
+					nskip++;
 			}
-			got_object_commit_close(commit);
-			commit = NULL;
-		} else {
-			/* should not happen */
-			err = got_error_fmt(GOT_ERR_NOT_IMPL,
-			    "%s ncolor=%d qcolor=%d", __func__, ncolor, qcolor);
-			break;
 		}
 
-		STAILQ_REMOVE_HEAD(ids, entry);
+		got_object_commit_close(commit);
+		commit = NULL;
 		got_object_qid_free(qid);
 	}
-
+done:
 	if (commit)
 		got_object_commit_close(commit);
 	return err;
@@ -1345,7 +1327,7 @@ findtwixt(struct got_object_id ***res, int *nres, int 
 {
 	const struct got_error *err = NULL;
 	struct got_object_id_queue ids;
-	struct got_object_idset *keep, *drop;
+	struct got_object_idset *keep, *drop, *skip = NULL;
 	int i, nkeep;
 
 	STAILQ_INIT(&ids);
@@ -1363,6 +1345,12 @@ findtwixt(struct got_object_id ***res, int *nres, int 
 		goto done;
 	}
 
+	skip = got_object_idset_alloc();
+	if (skip == NULL) {
+		err = got_error_from_errno("got_object_idset_alloc");
+		goto done;
+	}
+
 	for (i = 0; i < nhead; i++) {
 		struct got_object_id *id = head[i];
 		if (id == NULL)
@@ -1381,8 +1369,9 @@ findtwixt(struct got_object_id ***res, int *nres, int 
 			goto done;
 	}
 
-	err = color_commits(ncolored, &ids, keep, drop, repo,
-	    progress_cb, progress_arg, rl, cancel_cb, cancel_arg);
+	err = paint_commits(ncolored, &ids, nhead + ntail,
+	    keep, drop, skip, repo, progress_cb, progress_arg, rl,
+	    cancel_cb, cancel_arg);
 	if (err)
 		goto done;
 
@@ -1394,18 +1383,22 @@ findtwixt(struct got_object_id ***res, int *nres, int 
 			err = got_error_from_errno("calloc");
 			goto done;
 		}
-		arg.idx = 0;
+		arg.idx = -1;
+		arg.skip = skip;
+		arg.drop = drop;
 		err = got_object_idset_for_each(keep, append_id, &arg);
 		if (err) {
 			free(arg.array);
 			goto done;
 		}
 		*res = arg.array;
-		*nres = nkeep;
+		*nres = arg.idx + 1;
 	}
 done:
 	got_object_idset_free(keep);
 	got_object_idset_free(drop);
+	if (skip)
+		got_object_idset_free(skip);
 	got_object_id_queue_free(&ids);
 	return err;
 }