[RFC PATCH 1/4] name-rev: improve name_rev() memory usage

[Alban Gruin <alban.gruin@gmail.com>]

name_rev() is a recursive function.  For each commit, it allocates the
name of its parents, and call itself.  A parent may not use a name for
multiple reasons, but in any case, the name will not be released.  On a
repository with a lot of branches, tags, remotes, and commits, it can
use more than 2GB of RAM.

To improve the situation, name_rev() now returns a boolean to its caller
indicating if it can release the name.  The caller may free the name if
the commit is too old, or if the new name is not better than the current
name.

There a condition that will always be false here when name_rev() calls
itself for the first parent, but it will become useful when name_rev()
will stop to name commits that are not mentionned in the stdin buffer.
If the current commit should not be named, its parents may have to be,
but they may not.  In this case, name_rev() will tell to its caller that
the current commit and its first parent has not used the name, and that
it can be released.  However, if the current commit has been named but
not its parent, or the reverse, the name will not be released.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
---
 builtin/name-rev.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/builtin/name-rev.c b/builtin/name-rev.c
index f1cb45c227..0719a9388d 100644
--- a/builtin/name-rev.c
+++ b/builtin/name-rev.c
@@ -77,7 +77,7 @@ static int is_better_name(struct rev_name *name,
 	return 0;
 }
 
-static void name_rev(struct commit *commit,
+static int name_rev(struct commit *commit,
 		const char *tip_name, timestamp_t taggerdate,
 		int generation, int distance, int from_tag,
 		int deref)
@@ -86,11 +86,12 @@ static void name_rev(struct commit *commit,
 	struct commit_list *parents;
 	int parent_number = 1;
 	char *to_free = NULL;
+	int free_alloc = 1;
 
 	parse_commit(commit);
 
 	if (commit->date < cutoff)
-		return;
+		return 1;
 
 	if (deref) {
 		tip_name = to_free = xstrfmt("%s^0", tip_name);
@@ -111,9 +112,10 @@ static void name_rev(struct commit *commit,
 		name->generation = generation;
 		name->distance = distance;
 		name->from_tag = from_tag;
+		free_alloc = 0;
 	} else {
 		free(to_free);
-		return;
+		return 1;
 	}
 
 	for (parents = commit->parents;
@@ -131,15 +133,18 @@ static void name_rev(struct commit *commit,
 				new_name = xstrfmt("%.*s^%d", (int)len, tip_name,
 						   parent_number);
 
-			name_rev(parents->item, new_name, taggerdate, 0,
-				 distance + MERGE_TRAVERSAL_WEIGHT,
-				 from_tag, 0);
+			if (name_rev(parents->item, new_name, taggerdate, 0,
+				      distance + MERGE_TRAVERSAL_WEIGHT,
+				      from_tag, 0))
+				free(new_name);
 		} else {
-			name_rev(parents->item, tip_name, taggerdate,
-				 generation + 1, distance + 1,
-				 from_tag, 0);
+			free_alloc &= name_rev(parents->item, tip_name, taggerdate,
+					       generation + 1, distance + 1,
+					       from_tag, 0);
 		}
 	}
+
+	return free_alloc;
 }
 
 static int subpath_matches(const char *path, const char *filter)
-- 
2.20.1