Subject: Re: [PATCH 08/15] name-rev: pull out deref handling from the recursion

From: SZEDER Gábor <[email-masked]>
Date: Sat, 21 Sep 2019 11:57:18 +0200

On Fri, Sep 20, 2019 at 08:14:07PM +0200, SZEDER Gábor wrote:
> On Fri, Sep 20, 2019 at 08:13:02PM +0200, SZEDER Gábor wrote:
> > > If the (re)introduced leak doesn't impact performance and memory
> > > usage too much then duplicating tip_name again in name_rev() or
> > > rather your new create_or_update_name() would likely make the
> > > lifetimes of those string buffers easier to manage.
> > 
> > Yeah, the easiest would be when each 'struct rev_name' in the commit
> > slab would have its own 'tip_name' string, but that would result in
> > a lot of duplicated strings and increased memory usage.
> 
> I didn't measure how much more memory would be used, though.

So, I tried the patch below to give each 'struct rev_name' instance
its own copy of 'tip_name', and the memory usage of 'git name-rev
--all' usually increased.

The increase depends on how many merges and how many refs there are
compared to the number of commits: the fewer merges and refs, the
higher the more the memory usage increased:

  linux:         +4.8%
  gcc:           +7.2% 
  gecko-dev:     +9.2%
  webkit:       +12.4%
  llvm-project: +19.0%

git.git is the exception with its unusually high number of merge
commits (about 25%), and the memory usage decresed by 4.4%.

 --- >8 ---

diff --git a/builtin/name-rev.c b/builtin/name-rev.c
index 6969af76c4..62ab78242b 100644
--- a/builtin/name-rev.c
+++ b/builtin/name-rev.c
@@ -88,6 +88,7 @@ static struct rev_name *create_or_update_name(struct commit *commit,
 		set_commit_rev_name(commit, name);
 		goto copy_data;
 	} else if (is_better_name(name, taggerdate, distance, from_tag)) {
+		free((char*) name->tip_name);
 copy_data:
 		name->tip_name = tip_name;
 		name->taggerdate = taggerdate;
@@ -106,21 +107,19 @@ static void name_rev(struct commit *start_commit,
 {
 	struct commit_list *list = NULL;
 	const char *tip_name;
-	char *to_free = NULL;
 
 	parse_commit(start_commit);
 	if (start_commit->date < cutoff)
 		return;
 
 	if (deref) {
-		tip_name = to_free = xstrfmt("%s^0", start_tip_name);
-		free((char*) start_tip_name);
+		tip_name = xstrfmt("%s^0", start_tip_name);
 	} else
-		tip_name = start_tip_name;
+		tip_name = strdup(start_tip_name);
 
 	if (!create_or_update_name(start_commit, tip_name, taggerdate, 0, 0,
 				   from_tag)) {
-		free(to_free);
+		free((char*) tip_name);
 		return;
 	}
 
@@ -139,7 +138,6 @@ static void name_rev(struct commit *start_commit,
 			struct commit *parent = parents->item;
 			const char *new_name;
 			int generation, distance;
-			const char *new_name_to_free = NULL;
 
 			parse_commit(parent);
 			if (parent->date < cutoff)
@@ -159,11 +157,10 @@ static void name_rev(struct commit *start_commit,
 					new_name = xstrfmt("%.*s^%d", (int)len,
 							   name->tip_name,
 							   parent_number);
-				new_name_to_free = new_name;
 				generation = 0;
 				distance = name->distance + MERGE_TRAVERSAL_WEIGHT;
 			} else {
-				new_name = name->tip_name;
+				new_name = strdup(name->tip_name);
 				generation = name->generation + 1;
 				distance = name->distance + 1;
 			}
@@ -174,7 +171,7 @@ static void name_rev(struct commit *start_commit,
 				last_new_parent = commit_list_append(parent,
 						  last_new_parent);
 			else
-				free((char*) new_name_to_free);
+				free((char*) new_name);
 		}
 
 		*last_new_parent = list;
@@ -313,7 +310,7 @@ static int name_ref(const char *path, const struct object_id *oid, int flags, vo
 		if (taggerdate == TIME_MAX)
 			taggerdate = commit->date;
 		path = name_ref_abbrev(path, can_abbreviate_output);
-		name_rev(commit, xstrdup(path), taggerdate, from_tag, deref);
+		name_rev(commit, path, taggerdate, from_tag, deref);
 	}
 	return 0;
 }
-- 
2.23.0.331.g4e51dcdf11