diff --git a/cache.h b/cache.h
index ce377e1354..55dd4e3c8e 100644
--- a/cache.h
+++ b/cache.h
@@ -1236,6 +1236,8 @@ __attribute__((format (printf, 2, 3)))
 extern void trace_argv_printf(const char **argv, const char *format, ...);
 extern void trace_repo_setup(const char *prefix);
 extern int trace_want(const char *key);
+__attribute__((format (printf, 2, 3)))
+extern void trace_printf_key(const char *key, const char *fmt, ...);
 extern void trace_strbuf(const char *key, const struct strbuf *buf);
 
 void packet_trace_identity(const char *prog);
diff --git a/commit.h b/commit.h
index 1faf717212..9ead93bffb 100644
--- a/commit.h
+++ b/commit.h
@@ -193,6 +193,8 @@ extern struct commit_list *get_octopus_merge_bases(struct commit_list *in);
 /* largest positive number a signed 32-bit integer can contain */
 #define INFINITE_DEPTH 0x7fffffff
 
+struct sha1_array;
+struct ref;
 extern int register_shallow(const unsigned char *sha1);
 extern int unregister_shallow(const unsigned char *sha1);
 extern int for_each_commit_graft(each_commit_graft_fn, void *);
@@ -209,6 +211,19 @@ extern void setup_alternate_shallow(struct lock_file *shallow_lock,
 extern char *setup_temporary_shallow(const struct sha1_array *extra);
 extern void advertise_shallow_grafts(int);
 
+struct shallow_info {
+	struct sha1_array *shallow;
+	int *ours, nr_ours;
+	int *theirs, nr_theirs;
+	struct sha1_array *ref;
+};
+
+extern void prepare_shallow_info(struct shallow_info *, struct sha1_array *);
+extern void clear_shallow_info(struct shallow_info *);
+extern void remove_nonexistent_theirs_shallow(struct shallow_info *);
+extern void remove_nonexistent_ours_in_pack(struct shallow_info *,
+					    struct packed_git *);
+
 int is_descendant_of(struct commit *, struct commit_list *);
 int in_merge_bases(struct commit *, struct commit *);
 int in_merge_bases_many(struct commit *, int, struct commit **);
diff --git a/shallow.c b/shallow.c
index 822c626600..ecd950fd04 100644
--- a/shallow.c
+++ b/shallow.c
@@ -2,6 +2,12 @@
 #include "commit.h"
 #include "tag.h"
 #include "pkt-line.h"
+#include "remote.h"
+#include "refs.h"
+#include "sha1-array.h"
+#include "diff.h"
+#include "revision.h"
+#include "commit-slab.h"
 
 static int is_shallow = -1;
 static struct stat shallow_stat;
@@ -245,3 +251,69 @@ void advertise_shallow_grafts(int fd)
 		return;
 	for_each_commit_graft(advertise_shallow_grafts_cb, &fd);
 }
+
+#define TRACE_KEY "GIT_TRACE_SHALLOW"
+
+/*
+ * Step 1, split sender shallow commits into "ours" and "theirs"
+ * Step 2, clean "ours" based on .git/shallow
+ */
+void prepare_shallow_info(struct shallow_info *info, struct sha1_array *sa)
+{
+	int i;
+	trace_printf_key(TRACE_KEY, "shallow: prepare_shallow_info\n");
+	memset(info, 0, sizeof(*info));
+	info->shallow = sa;
+	if (!sa)
+		return;
+	info->ours = xmalloc(sizeof(*info->ours) * sa->nr);
+	info->theirs = xmalloc(sizeof(*info->theirs) * sa->nr);
+	for (i = 0; i < sa->nr; i++) {
+		if (has_sha1_file(sa->sha1[i])) {
+			struct commit_graft *graft;
+			graft = lookup_commit_graft(sa->sha1[i]);
+			if (graft && graft->nr_parent < 0)
+				continue;
+			info->ours[info->nr_ours++] = i;
+		} else
+			info->theirs[info->nr_theirs++] = i;
+	}
+}
+
+void clear_shallow_info(struct shallow_info *info)
+{
+	free(info->ours);
+	free(info->theirs);
+}
+
+/* Step 4, remove non-existent ones in "theirs" after getting the pack */
+
+void remove_nonexistent_theirs_shallow(struct shallow_info *info)
+{
+	unsigned char (*sha1)[20] = info->shallow->sha1;
+	int i, dst;
+	trace_printf_key(TRACE_KEY, "shallow: remove_nonexistent_theirs_shallow\n");
+	for (i = dst = 0; i < info->nr_theirs; i++) {
+		if (i != dst)
+			info->theirs[dst] = info->theirs[i];
+		if (has_sha1_file(sha1[info->theirs[i]]))
+			dst++;
+	}
+	info->nr_theirs = dst;
+}
+
+/* Step 5, remove non-existent ones in "ours" in the pack */
+void remove_nonexistent_ours_in_pack(struct shallow_info *info,
+				     struct packed_git *p)
+{
+	unsigned char (*sha1)[20] = info->shallow->sha1;
+	int i, dst;
+	trace_printf_key(TRACE_KEY, "shallow: remove_nonexistent_ours_in_pack\n");
+	for (i = dst = 0; i < info->nr_ours; i++) {
+		if (i != dst)
+			info->ours[dst] = info->ours[i];
+		if (find_pack_entry_one(sha1[info->ours[i]], p))
+			dst++;
+	}
+	info->nr_ours = dst;
+}
diff --git a/trace.c b/trace.c
index 3d744d1d4d..08180a90bc 100644
--- a/trace.c
+++ b/trace.c
@@ -76,7 +76,7 @@ static void trace_vprintf(const char *key, const char *fmt, va_list ap)
 }
 
 __attribute__((format (printf, 2, 3)))
-static void trace_printf_key(const char *key, const char *fmt, ...)
+void trace_printf_key(const char *key, const char *fmt, ...)
 {
 	va_list ap;
 	va_start(ap, fmt);