Merge branch 'tb/multi-pack-reuse-experiment'

Setting `feature.experimental` opts the user into multi-pack reuse
experiment

* tb/multi-pack-reuse-experiment:
  pack-objects: enable multi-pack reuse via `feature.experimental`
  t5332-multi-pack-reuse.sh: extract pack-objects helper functions

Documentation/config/feature.txt

@@ -17,6 +17,9 @@ skipping more commits at a time, reducing the number of round trips.
 +
 * `pack.useBitmapBoundaryTraversal=true` may improve bitmap traversal times by
 walking fewer objects.
++
+* `pack.allowPackReuse=multi` may improve the time it takes to create a pack by
+reusing objects from multiple packs instead of just one.
 
 feature.manyFiles::
 	Enable config options that optimize for repos with many files in the

builtin/pack-objects.c

@@ -4396,6 +4396,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 		prepare_repo_settings(the_repository);
 		if (sparse < 0)
 			sparse = the_repository->settings.pack_use_sparse;
+		if (the_repository->settings.pack_use_multi_pack_reuse)
+			allow_pack_reuse = MULTI_PACK_REUSE;
 	}
 
 	reset_pack_idx_option(&pack_idx_opts);

repo-settings.c

@@ -43,6 +43,7 @@ void prepare_repo_settings(struct repository *r)
 	if (experimental) {
 		r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
 		r->settings.pack_use_bitmap_boundary_traversal = 1;
+		r->settings.pack_use_multi_pack_reuse = 1;
 	}
 	if (manyfiles) {
 		r->settings.index_version = 4;

repository.h

@@ -39,6 +39,7 @@ struct repo_settings {
 	int sparse_index;
 	int pack_read_reverse_index;
 	int pack_use_bitmap_boundary_traversal;
+	int pack_use_multi_pack_reuse;
 
 	/*
 	 * Does this repository have core.useReplaceRefs=true (on by

t/t5332-multi-pack-reuse.sh

@@ -24,6 +24,27 @@ pack_position () {
 	grep "$1" objects | cut -d" " -f1
 }
 
+# test_pack_objects_reused_all <pack-reused> <packs-reused>
+test_pack_objects_reused_all () {
+	: >trace2.txt &&
+	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
+		git pack-objects --stdout --revs --all --delta-base-offset \
+		>/dev/null &&
+
+	test_pack_reused "$1" <trace2.txt &&
+	test_packs_reused "$2" <trace2.txt
+}
+
+# test_pack_objects_reused <pack-reused> <packs-reused>
+test_pack_objects_reused () {
+	: >trace2.txt &&
+	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
+		git pack-objects --stdout --revs >/dev/null &&
+
+	test_pack_reused "$1" <trace2.txt &&
+	test_packs_reused "$2" <trace2.txt
+}
+
 test_expect_success 'preferred pack is reused for single-pack reuse' '
 	test_config pack.allowPackReuse single &&
 
@@ -35,12 +56,24 @@ test_expect_success 'preferred pack is reused for single-pack reuse' '
 
 	git multi-pack-index write --bitmap &&
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --revs --all >/dev/null &&
+	test_pack_objects_reused_all 3 1
+'
 
-	test_pack_reused 3 <trace2.txt &&
-	test_packs_reused 1 <trace2.txt
+test_expect_success 'multi-pack reuse is disabled by default' '
+	test_pack_objects_reused_all 3 1
+'
+
+test_expect_success 'feature.experimental implies multi-pack reuse' '
+	test_config feature.experimental true &&
+
+	test_pack_objects_reused_all 6 2
+'
+
+test_expect_success 'multi-pack reuse can be disabled with feature.experimental' '
+	test_config feature.experimental true &&
+	test_config pack.allowPackReuse single &&
+
+	test_pack_objects_reused_all 3 1
 '
 
 test_expect_success 'enable multi-pack reuse' '
@@ -58,21 +91,11 @@ test_expect_success 'reuse all objects from subset of bitmapped packs' '
 	^$(git rev-parse A)
 	EOF
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --revs <in >/dev/null &&
-
-	test_pack_reused 6 <trace2.txt &&
-	test_packs_reused 2 <trace2.txt
+	test_pack_objects_reused 6 2 <in
 '
 
 test_expect_success 'reuse all objects from all packs' '
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --revs --all >/dev/null &&
-
-	test_pack_reused 9 <trace2.txt &&
-	test_packs_reused 3 <trace2.txt
+	test_pack_objects_reused_all 9 3
 '
 
 test_expect_success 'reuse objects from first pack with middle gap' '
@@ -105,12 +128,7 @@ test_expect_success 'reuse objects from first pack with middle gap' '
 	^$(git rev-parse D)
 	EOF
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --delta-base-offset --revs <in >/dev/null &&
-
-	test_pack_reused 3 <trace2.txt &&
-	test_packs_reused 1 <trace2.txt
+	test_pack_objects_reused 3 1 <in
 '
 
 test_expect_success 'reuse objects from middle pack with middle gap' '
@@ -126,12 +144,7 @@ test_expect_success 'reuse objects from middle pack with middle gap' '
 	^$(git rev-parse D)
 	EOF
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --delta-base-offset --revs <in >/dev/null &&
-
-	test_pack_reused 3 <trace2.txt &&
-	test_packs_reused 1 <trace2.txt
+	test_pack_objects_reused 3 1 <in
 '
 
 test_expect_success 'omit delta with uninteresting base (same pack)' '
@@ -161,10 +174,6 @@ test_expect_success 'omit delta with uninteresting base (same pack)' '
 	^$base
 	EOF
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --delta-base-offset --revs <in >/dev/null &&
-
 	# We can only reuse the 3 objects corresponding to "other" from
 	# the latest pack.
 	#
@@ -176,8 +185,7 @@ test_expect_success 'omit delta with uninteresting base (same pack)' '
 	# The remaining objects from the other pack are similarly not
 	# reused because their objects are on the uninteresting side of
 	# the query.
-	test_pack_reused 3 <trace2.txt &&
-	test_packs_reused 1 <trace2.txt
+	test_pack_objects_reused 3 1 <in
 '
 
 test_expect_success 'omit delta from uninteresting base (cross pack)' '
@@ -190,15 +198,10 @@ test_expect_success 'omit delta from uninteresting base (cross pack)' '
 
 	git multi-pack-index write --bitmap --preferred-pack="pack-$P.idx" &&
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --delta-base-offset --all >/dev/null &&
-
 	packs_nr="$(find $packdir -type f -name "pack-*.pack" | wc -l)" &&
 	objects_nr="$(git rev-list --count --all --objects)" &&
 
-	test_pack_reused $(($objects_nr - 1)) <trace2.txt &&
-	test_packs_reused $packs_nr <trace2.txt
+	test_pack_objects_reused_all $(($objects_nr - 1)) $packs_nr
 '
 
 test_done