From 64404a24cf60761baba0e04a337c419f0e86c0f9 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 29 Apr 2019 09:18:55 -0700
Subject: midx: pass a repository pointer

Much of the multi-pack-index code focuses on the multi_pack_index
struct, and so we only pass a pointer to the current one. However,
we will insert a dependency on the packed_git linked list in a
future change, so we will need a repository reference. Inserting
these parameters is a significant enough change to split out.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index ae6e476..72dfd3d 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -46,7 +46,7 @@ int cmd_multi_pack_index(int argc, const char **argv,
 	if (!strcmp(argv[0], "write"))
 		return write_midx_file(opts.object_dir);
 	if (!strcmp(argv[0], "verify"))
-		return verify_midx_file(opts.object_dir);
+		return verify_midx_file(the_repository, opts.object_dir);
 
 	die(_("unrecognized verb: %s"), argv[0]);
 }
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 2d9a3bd..e606b9e 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1078,7 +1078,7 @@ static int want_object_in_pack(const struct object_id *oid,
 
 	for (m = get_multi_pack_index(the_repository); m; m = m->next) {
 		struct pack_entry e;
-		if (fill_midx_entry(oid, &e, m)) {
+		if (fill_midx_entry(the_repository, oid, &e, m)) {
 			struct packed_git *p = e.p;
 			off_t offset;
 
diff --git a/midx.c b/midx.c
index d5d2e95..8b8faec 100644
--- a/midx.c
+++ b/midx.c
@@ -201,7 +201,7 @@ void close_midx(struct multi_pack_index *m)
 	FREE_AND_NULL(m->pack_names);
 }
 
-int prepare_midx_pack(struct multi_pack_index *m, uint32_t pack_int_id)
+int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id)
 {
 	struct strbuf pack_name = STRBUF_INIT;
 
@@ -261,7 +261,10 @@ static uint32_t nth_midxed_pack_int_id(struct multi_pack_index *m, uint32_t pos)
 	return get_be32(m->chunk_object_offsets + pos * MIDX_CHUNK_OFFSET_WIDTH);
 }
 
-static int nth_midxed_pack_entry(struct multi_pack_index *m, struct pack_entry *e, uint32_t pos)
+static int nth_midxed_pack_entry(struct repository *r,
+				 struct multi_pack_index *m,
+				 struct pack_entry *e,
+				 uint32_t pos)
 {
 	uint32_t pack_int_id;
 	struct packed_git *p;
@@ -271,7 +274,7 @@ static int nth_midxed_pack_entry(struct multi_pack_index *m, struct pack_entry *
 
 	pack_int_id = nth_midxed_pack_int_id(m, pos);
 
-	if (prepare_midx_pack(m, pack_int_id))
+	if (prepare_midx_pack(r, m, pack_int_id))
 		die(_("error preparing packfile from multi-pack-index"));
 	p = m->packs[pack_int_id];
 
@@ -301,14 +304,17 @@ static int nth_midxed_pack_entry(struct multi_pack_index *m, struct pack_entry *
 	return 1;
 }
 
-int fill_midx_entry(const struct object_id *oid, struct pack_entry *e, struct multi_pack_index *m)
+int fill_midx_entry(struct repository * r,
+		    const struct object_id *oid,
+		    struct pack_entry *e,
+		    struct multi_pack_index *m)
 {
 	uint32_t pos;
 
 	if (!bsearch_midx(oid, m, &pos))
 		return 0;
 
-	return nth_midxed_pack_entry(m, e, pos);
+	return nth_midxed_pack_entry(r, m, e, pos);
 }
 
 /* Match "foo.idx" against either "foo.pack" _or_ "foo.idx". */
@@ -1020,7 +1026,7 @@ static int compare_pair_pos_vs_id(const void *_a, const void *_b)
 			display_progress(progress, _n); \
 	} while (0)
 
-int verify_midx_file(const char *object_dir)
+int verify_midx_file(struct repository *r, const char *object_dir)
 {
 	struct pair_pos_vs_id *pairs = NULL;
 	uint32_t i;
@@ -1034,7 +1040,7 @@ int verify_midx_file(const char *object_dir)
 	progress = start_progress(_("Looking for referenced packfiles"),
 				  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
-		if (prepare_midx_pack(m, i))
+		if (prepare_midx_pack(r, m, i))
 			midx_report("failed to load pack in position %d", i);
 
 		display_progress(progress, i + 1);
@@ -1099,7 +1105,7 @@ int verify_midx_file(const char *object_dir)
 
 		nth_midxed_object_oid(&oid, m, pairs[i].pos);
 
-		if (!fill_midx_entry(&oid, &e, m)) {
+		if (!fill_midx_entry(r, &oid, &e, m)) {
 			midx_report(_("failed to load pack entry for oid[%d] = %s"),
 				    pairs[i].pos, oid_to_hex(&oid));
 			continue;
diff --git a/midx.h b/midx.h
index 26dd042..3eb2973 100644
--- a/midx.h
+++ b/midx.h
@@ -5,6 +5,7 @@
 
 struct object_id;
 struct pack_entry;
+struct repository;
 
 #define GIT_TEST_MULTI_PACK_INDEX "GIT_TEST_MULTI_PACK_INDEX"
 
@@ -37,18 +38,18 @@ struct multi_pack_index {
 };
 
 struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local);
-int prepare_midx_pack(struct multi_pack_index *m, uint32_t pack_int_id);
+int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
 int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result);
 struct object_id *nth_midxed_object_oid(struct object_id *oid,
 					struct multi_pack_index *m,
 					uint32_t n);
-int fill_midx_entry(const struct object_id *oid, struct pack_entry *e, struct multi_pack_index *m);
+int fill_midx_entry(struct repository *r, const struct object_id *oid, struct pack_entry *e, struct multi_pack_index *m);
 int midx_contains_pack(struct multi_pack_index *m, const char *idx_or_pack_name);
 int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, int local);
 
 int write_midx_file(const char *object_dir);
 void clear_midx_file(struct repository *r);
-int verify_midx_file(const char *object_dir);
+int verify_midx_file(struct repository *r, const char *object_dir);
 
 void close_midx(struct multi_pack_index *m);
 
diff --git a/packfile.c b/packfile.c
index cdf6b6e..7b94a14 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1035,7 +1035,7 @@ struct packed_git *get_all_packs(struct repository *r)
 		for (m = r->objects->multi_pack_index; m; m = m->next) {
 			uint32_t i;
 			for (i = 0; i < m->num_packs; i++) {
-				if (!prepare_midx_pack(m, i)) {
+				if (!prepare_midx_pack(r, m, i)) {
 					m->packs[i]->next = p;
 					p = m->packs[i];
 				}
@@ -1998,7 +1998,7 @@ int find_pack_entry(struct repository *r, const struct object_id *oid, struct pa
 		return 0;
 
 	for (m = r->objects->multi_pack_index; m; m = m->next) {
-		if (fill_midx_entry(oid, e, m))
+		if (fill_midx_entry(r, oid, e, m))
 			return 1;
 	}
 
-- 
cgit v0.10.2-6-g49f6


From af96fe3392fb078cb5447bcb94f2ed8d79d0a4a8 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 29 Apr 2019 09:18:56 -0700
Subject: midx: add packs to packed_git linked list

The multi-pack-index allows searching for objects across multiple
packs using one object list. The original design gains many of
these performance benefits by keeping the packs in the
multi-pack-index out of the packed_git list.

Unfortunately, this has one major drawback. If the multi-pack-index
covers thousands of packs, and a command loads many of those packs,
then we can hit the limit for open file descriptors. The
close_one_pack() method is used to limit this resource, but it
only looks at the packed_git list, and uses an LRU cache to prevent
thrashing.

Instead of complicating this close_one_pack() logic to include
direct references to the multi-pack-index, simply add the packs
opened by the multi-pack-index to the packed_git list. This
immediately solves the file-descriptor limit problem, but requires
some extra steps to avoid performance issues or other problems:

1. Create a multi_pack_index bit in the packed_git struct that is
   one if and only if the pack was loaded from a multi-pack-index.

2. Skip packs with the multi_pack_index bit when doing object
   lookups and abbreviations. These algorithms already check the
   multi-pack-index before the packed_git struct. This has a very
   small performance hit, as we need to walk more packed_git
   structs. This is acceptable, since these operations run binary
   search on the other packs, so this walk-and-ignore logic is
   very fast by comparison.

3. When closing a multi-pack-index file, do not close its packs,
   as those packs will be closed using close_all_packs(). In some
   cases, such as 'git repack', we run 'close_midx()' without also
   closing the packs, so we need to un-set the multi_pack_index bit
   in those packs. This is necessary, and caught by running
   t6501-freshen-objects.sh with GIT_TEST_MULTI_PACK_INDEX=1.

To manually test this change, I inserted trace2 logging into
close_pack_fd() and set pack_max_fds to 10, then ran 'git rev-list
--all --objects' on a copy of the Git repo with 300+ pack-files and
a multi-pack-index. The logs verified the packs are closed as
we read them beyond the file descriptor limit.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/midx.c b/midx.c
index 8b8faec..e7e1fe4 100644
--- a/midx.c
+++ b/midx.c
@@ -192,10 +192,8 @@ void close_midx(struct multi_pack_index *m)
 	m->fd = -1;
 
 	for (i = 0; i < m->num_packs; i++) {
-		if (m->packs[i]) {
-			close_pack(m->packs[i]);
-			free(m->packs[i]);
-		}
+		if (m->packs[i])
+			m->packs[i]->multi_pack_index = 0;
 	}
 	FREE_AND_NULL(m->packs);
 	FREE_AND_NULL(m->pack_names);
@@ -204,6 +202,7 @@ void close_midx(struct multi_pack_index *m)
 int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id)
 {
 	struct strbuf pack_name = STRBUF_INIT;
+	struct packed_git *p;
 
 	if (pack_int_id >= m->num_packs)
 		die(_("bad pack-int-id: %u (%u total packs)"),
@@ -215,9 +214,18 @@ int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t
 	strbuf_addf(&pack_name, "%s/pack/%s", m->object_dir,
 		    m->pack_names[pack_int_id]);
 
-	m->packs[pack_int_id] = add_packed_git(pack_name.buf, pack_name.len, m->local);
+	p = add_packed_git(pack_name.buf, pack_name.len, m->local);
 	strbuf_release(&pack_name);
-	return !m->packs[pack_int_id];
+
+	if (!p)
+		return 1;
+
+	p->multi_pack_index = 1;
+	m->packs[pack_int_id] = p;
+	install_packed_git(r, p);
+	list_add_tail(&p->mru, &r->objects->packed_git_mru);
+
+	return 0;
 }
 
 int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result)
diff --git a/object-store.h b/object-store.h
index b086f5e..7acbc7f 100644
--- a/object-store.h
+++ b/object-store.h
@@ -76,7 +76,8 @@ struct packed_git {
 		 pack_keep_in_core:1,
 		 freshened:1,
 		 do_not_close:1,
-		 pack_promisor:1;
+		 pack_promisor:1,
+		 multi_pack_index:1;
 	unsigned char hash[GIT_MAX_RAWSZ];
 	struct revindex_entry *revindex;
 	/* something like ".git/objects/pack/xxxxx.pack" */
@@ -129,12 +130,6 @@ struct raw_object_store {
 	struct list_head packed_git_mru;
 
 	/*
-	 * A linked list containing all packfiles, starting with those
-	 * contained in the multi_pack_index.
-	 */
-	struct packed_git *all_packs;
-
-	/*
 	 * A fast, rough count of the number of objects in the repository.
 	 * These two fields are not meant for direct access. Use
 	 * approximate_object_count() instead.
diff --git a/packfile.c b/packfile.c
index 7b94a14..060de42 100644
--- a/packfile.c
+++ b/packfile.c
@@ -994,8 +994,6 @@ static void prepare_packed_git(struct repository *r)
 	}
 	rearrange_packed_git(r);
 
-	r->objects->all_packs = NULL;
-
 	prepare_packed_git_mru(r);
 	r->objects->packed_git_initialized = 1;
 }
@@ -1026,26 +1024,16 @@ struct multi_pack_index *get_multi_pack_index(struct repository *r)
 
 struct packed_git *get_all_packs(struct repository *r)
 {
-	prepare_packed_git(r);
-
-	if (!r->objects->all_packs) {
-		struct packed_git *p = r->objects->packed_git;
-		struct multi_pack_index *m;
-
-		for (m = r->objects->multi_pack_index; m; m = m->next) {
-			uint32_t i;
-			for (i = 0; i < m->num_packs; i++) {
-				if (!prepare_midx_pack(r, m, i)) {
-					m->packs[i]->next = p;
-					p = m->packs[i];
-				}
-			}
-		}
+	struct multi_pack_index *m;
 
-		r->objects->all_packs = p;
+	prepare_packed_git(r);
+	for (m = r->objects->multi_pack_index; m; m = m->next) {
+		uint32_t i;
+		for (i = 0; i < m->num_packs; i++)
+			prepare_midx_pack(r, m, i);
 	}
 
-	return r->objects->all_packs;
+	return r->objects->packed_git;
 }
 
 struct list_head *get_packed_git_mru(struct repository *r)
@@ -2004,7 +1992,7 @@ int find_pack_entry(struct repository *r, const struct object_id *oid, struct pa
 
 	list_for_each(pos, &r->objects->packed_git_mru) {
 		struct packed_git *p = list_entry(pos, struct packed_git, mru);
-		if (fill_pack_entry(oid, e, p)) {
+		if (!p->multi_pack_index && fill_pack_entry(oid, e, p)) {
 			list_move(&p->mru, &r->objects->packed_git_mru);
 			return 1;
 		}
diff --git a/sha1-name.c b/sha1-name.c
index 07c71a7..42ac1c5 100644
--- a/sha1-name.c
+++ b/sha1-name.c
@@ -157,6 +157,9 @@ static void unique_in_pack(struct packed_git *p,
 	uint32_t num, i, first = 0;
 	const struct object_id *current = NULL;
 
+	if (p->multi_pack_index)
+		return;
+
 	if (open_pack_index(p) || !p->num_objects)
 		return;
 
@@ -589,6 +592,9 @@ static void find_abbrev_len_for_pack(struct packed_git *p,
 	struct object_id oid;
 	const struct object_id *mad_oid;
 
+	if (p->multi_pack_index)
+		return;
+
 	if (open_pack_index(p) || !p->num_objects)
 		return;
 
-- 
cgit v0.10.2-6-g49f6