Re: [PATCH v2 1/5] speed up alt_odb_usable() with many alternates

From: "René Scharfe" <l.s.r@web.de>
To: Eric Wong <e@80x24.org>, git@vger.kernel.org
Cc: Jeff King <peff@peff.net>
Subject: Re: [PATCH v2 1/5] speed up alt_odb_usable() with many alternates
Date: Sun, 4 Jul 2021 11:02:19 +0200	[thread overview]
Message-ID: <d069bc0b-f989-0d15-61ec-19f85841bc51@web.de> (raw)
In-Reply-To: <fc342ddd-1b35-62cc-dd4b-e0462d595819@web.de>

Am 03.07.21 um 12:05 schrieb René Scharfe:
> Am 29.06.21 um 22:53 schrieb Eric Wong:
>> +	*pos = kh_put_odb_path_map(o->odb_by_path, path->buf, &r);
>> +	if (r < 0) die_errno(_("kh_put_odb_path_map"));

>> +	/* r: 0 = exists, 1 = never used, 2 = deleted */
>> +	return r == 0 ? 0 : 1;

> I like the solution in oidset.c to make this more readable, though: Call
> the return value "added" instead of "r" and then a "return !added;"
> makes sense without additional comments.

That's probably because I wrote that part; see 8b2f8cbcb1 (oidset: use
khash, 2018-10-04) -- I had somehow forgotten about that. o_O

And here we wouldn't negate.  Passing on the value verbatim, without
normalizing 2 to 1, would work fine.

alt_odb_usable() and its caller become quite entangled due to the
hashmap insert operation being split between them.  I suspect the code
would improve by inlining the function in a follow-up patch, making
return code considerations moot.  The improvement is not significant
enough to hold up this series in case you don't like the idea, though.

Rough demo:

 object-file.c | 82 +++++++++++++++++++++++++++--------------------------------
 1 file changed, 37 insertions(+), 45 deletions(-)

diff --git a/object-file.c b/object-file.c
index 304af3a172..a5e91091ee 100644
--- a/object-file.c
+++ b/object-file.c
@@ -512,45 +512,6 @@ const char *loose_object_path(struct repository *r, struct strbuf *buf,
 	return odb_loose_path(r->objects->odb, buf, oid);
 }

-/*
- * Return non-zero iff the path is usable as an alternate object database.
- */
-static int alt_odb_usable(struct raw_object_store *o,
-			  struct strbuf *path,
-			  const char *normalized_objdir, khiter_t *pos)
-{
-	int r;
-
-	/* Detect cases where alternate disappeared */
-	if (!is_directory(path->buf)) {
-		error(_("object directory %s does not exist; "
-			"check .git/objects/info/alternates"),
-		      path->buf);
-		return 0;
-	}
-
-	/*
-	 * Prevent the common mistake of listing the same
-	 * thing twice, or object directory itself.
-	 */
-	if (!o->odb_by_path) {
-		khiter_t p;
-
-		o->odb_by_path = kh_init_odb_path_map();
-		assert(!o->odb->next);
-		p = kh_put_odb_path_map(o->odb_by_path, o->odb->path, &r);
-		if (r < 0) die_errno(_("kh_put_odb_path_map"));
-		assert(r == 1); /* never used */
-		kh_value(o->odb_by_path, p) = o->odb;
-	}
-	if (!fspathcmp(path->buf, normalized_objdir))
-		return 0;
-	*pos = kh_put_odb_path_map(o->odb_by_path, path->buf, &r);
-	if (r < 0) die_errno(_("kh_put_odb_path_map"));
-	/* r: 0 = exists, 1 = never used, 2 = deleted */
-	return r == 0 ? 0 : 1;
-}
-
 /*
  * Prepare alternate object database registry.
  *
@@ -575,6 +536,9 @@ static int link_alt_odb_entry(struct repository *r, const char *entry,
 	struct object_directory *ent;
 	struct strbuf pathbuf = STRBUF_INIT;
 	khiter_t pos;
+	int ret = -1;
+	int added;
+	struct raw_object_store *o = r->objects;

 	if (!is_absolute_path(entry) && relative_base) {
 		strbuf_realpath(&pathbuf, relative_base, 1);
@@ -585,8 +549,7 @@ static int link_alt_odb_entry(struct repository *r, const char *entry,
 	if (strbuf_normalize_path(&pathbuf) < 0 && relative_base) {
 		error(_("unable to normalize alternate object path: %s"),
 		      pathbuf.buf);
-		strbuf_release(&pathbuf);
-		return -1;
+		goto out;
 	}

 	/*
@@ -596,11 +559,37 @@ static int link_alt_odb_entry(struct repository *r, const char *entry,
 	while (pathbuf.len && pathbuf.buf[pathbuf.len - 1] == '/')
 		strbuf_setlen(&pathbuf, pathbuf.len - 1);

-	if (!alt_odb_usable(r->objects, &pathbuf, normalized_objdir, &pos)) {
-		strbuf_release(&pathbuf);
-		return -1;
+	/* Detect cases where alternate disappeared */
+	if (!is_directory(pathbuf.buf)) {
+		error(_("object directory %s does not exist; "
+			"check .git/objects/info/alternates"),
+		      pathbuf.buf);
+		goto out;
+	}
+
+	/*
+	 * Prevent the common mistake of listing the same
+	 * thing twice, or object directory itself.
+	 */
+	if (!o->odb_by_path) {
+		khiter_t p;
+
+		o->odb_by_path = kh_init_odb_path_map();
+		assert(!o->odb->next);
+		p = kh_put_odb_path_map(o->odb_by_path, o->odb->path, &added);
+		if (added < 0) die_errno(_("kh_put_odb_path_map"));
+		assert(added);
+		kh_value(o->odb_by_path, p) = o->odb;
 	}

+	if (!fspathcmp(pathbuf.buf, normalized_objdir))
+		goto out;
+
+	pos = kh_put_odb_path_map(o->odb_by_path, pathbuf.buf, &added);
+	if (added < 0) die_errno(_("kh_put_odb_path_map"));
+	if (!added)
+		goto out;
+
 	CALLOC_ARRAY(ent, 1);
 	/* pathbuf.buf is already in r->objects->odb_by_path */
 	ent->path = strbuf_detach(&pathbuf, NULL);
@@ -615,7 +604,10 @@ static int link_alt_odb_entry(struct repository *r, const char *entry,
 	/* recursively add alternates */
 	read_info_alternates(r, ent->path, depth + 1);

-	return 0;
+	ret = 0;
+out:
+	strbuf_release(&pathbuf);
+	return ret;
 }

 static const char *parse_alt_odb_entry(const char *string,

