[PATCH v2] fetch-pack: grow stateless RPC windows exponentially

[Jonathan Tan <jonathantanmy@google.com>]

When updating large repositories, the LARGE_FLUSH limit (that is, the
limit at which the window growth strategy switches from exponential to
linear) is reached quite quickly. Use a conservative exponential growth
strategy when that limit is reached instead (and increase LARGE_FLUSH so
that there is no regression in window size).

This optimization is only applied during stateless RPCs to avoid the
issue raised and fixed in commit
44d8dc54e73e8010c4bdf57a422fc8d5ce709029.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
 fetch-pack.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/fetch-pack.c b/fetch-pack.c
index b501d5c..85e77af 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -243,16 +243,21 @@ static void insert_one_alternate_ref(const struct ref *ref, void *unused)
 
 #define INITIAL_FLUSH 16
 #define PIPESAFE_FLUSH 32
-#define LARGE_FLUSH 1024
+#define LARGE_FLUSH 16384
 
 static int next_flush(struct fetch_pack_args *args, int count)
 {
-	int flush_limit = args->stateless_rpc ? LARGE_FLUSH : PIPESAFE_FLUSH;
-
-	if (count < flush_limit)
-		count <<= 1;
-	else
-		count += flush_limit;
+	if (args->stateless_rpc) {
+		if (count < LARGE_FLUSH)
+			count <<= 1;
+		else
+			count = count * 11 / 10;
+	} else {
+		if (count < PIPESAFE_FLUSH)
+			count <<= 1;
+		else
+			count += PIPESAFE_FLUSH;
+	}
 	return count;
 }
 
-- 
2.8.0.rc3.226.g39d4020