Merge branch 'gs/commit-graph-path-filter'

Introduce an extension to the commit-graph to make it efficient to
check for the paths that were modified at each commit using Bloom
filters.

* gs/commit-graph-path-filter:
  bloom: ignore renames when computing changed paths
  commit-graph: add GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS test flag
  t4216: add end to end tests for git log with Bloom filters
  revision.c: add trace2 stats around Bloom filter usage
  revision.c: use Bloom filters to speed up path based revision walks
  commit-graph: add --changed-paths option to write subcommand
  commit-graph: reuse existing Bloom filters during write
  commit-graph: write Bloom filters to commit graph file
  commit-graph: examine commits by generation number
  commit-graph: examine changed-path objects in pack order
  commit-graph: compute Bloom filters for changed paths
  diff: halt tree-diff early after max_changes
  bloom.c: core Bloom filter implementation for changed paths.
  bloom.c: introduce core Bloom filter constructs
  bloom.c: add the murmur3 hash implementation
  commit-graph: define and use MAX_NUM_CHUNKS

Documentation/git-commit-graph.txt

@@ -57,6 +57,11 @@ or `--stdin-packs`.)
 With the `--append` option, include all commits that are present in the
 existing commit-graph file.
 +
+With the `--changed-paths` option, compute and write information about the
+paths changed between a commit and it's first parent. This operation can
+take a while on large repositories. It provides significant performance gains
+for getting history of a directory or a file with `git log -- <path>`.
++
 With the `--split[=<strategy>]` option, write the commit-graph as a
 chain of multiple commit-graph files stored in
 `<dir>/info/commit-graphs`. Commit-graph layers are merged based on the

Documentation/technical/commit-graph-format.txt

@@ -17,6 +17,9 @@ metadata, including:
 - The parents of the commit, stored using positional references within
   the graph file.
 
+- The Bloom filter of the commit carrying the paths that were changed between
+  the commit and its first parent, if requested.
+
 These positional references are stored as unsigned 32-bit integers
 corresponding to the array position within the list of commit OIDs. Due
 to some special constants we use to track parents, we can store at most
@@ -93,6 +96,33 @@ CHUNK DATA:
       positions for the parents until reaching a value with the most-significant
       bit on. The other bits correspond to the position of the last parent.
 
+  Bloom Filter Index (ID: {'B', 'I', 'D', 'X'}) (N * 4 bytes) [Optional]
+    * The ith entry, BIDX[i], stores the number of 8-byte word blocks in all
+      Bloom filters from commit 0 to commit i (inclusive) in lexicographic
+      order. The Bloom filter for the i-th commit spans from BIDX[i-1] to
+      BIDX[i] (plus header length), where BIDX[-1] is 0.
+    * The BIDX chunk is ignored if the BDAT chunk is not present.
+
+  Bloom Filter Data (ID: {'B', 'D', 'A', 'T'}) [Optional]
+    * It starts with header consisting of three unsigned 32-bit integers:
+      - Version of the hash algorithm being used. We currently only support
+	value 1 which corresponds to the 32-bit version of the murmur3 hash
+	implemented exactly as described in
+	https://en.wikipedia.org/wiki/MurmurHash#Algorithm and the double
+	hashing technique using seed values 0x293ae76f and 0x7e646e2 as
+	described in https://doi.org/10.1007/978-3-540-30494-4_26 "Bloom Filters
+	in Probabilistic Verification"
+      - The number of times a path is hashed and hence the number of bit positions
+	      that cumulatively determine whether a file is present in the commit.
+      - The minimum number of bits 'b' per entry in the Bloom filter. If the filter
+	      contains 'n' entries, then the filter size is the minimum number of 64-bit
+	      words that contain n*b bits.
+    * The rest of the chunk is the concatenation of all the computed Bloom
+      filters for the commits in lexicographic order.
+    * Note: Commits with no changes or more than 512 changes have Bloom filters
+      of length zero.
+    * The BDAT chunk is present if and only if BIDX is present.
+
   Base Graphs List (ID: {'B', 'A', 'S', 'E'}) [Optional]
       This list of H-byte hashes describe a set of B commit-graph files that
       form a commit-graph chain. The graph position for the ith commit in this

Makefile

@@ -689,6 +689,7 @@ X =
 PROGRAMS += $(patsubst %.o,git-%$X,$(PROGRAM_OBJS))
 
 TEST_BUILTINS_OBJS += test-advise.o
+TEST_BUILTINS_OBJS += test-bloom.o
 TEST_BUILTINS_OBJS += test-chmtime.o
 TEST_BUILTINS_OBJS += test-config.o
 TEST_BUILTINS_OBJS += test-ctype.o
@@ -834,6 +835,7 @@ LIB_OBJS += base85.o
 LIB_OBJS += bisect.o
 LIB_OBJS += blame.o
 LIB_OBJS += blob.o
+LIB_OBJS += bloom.o
 LIB_OBJS += branch.o
 LIB_OBJS += bulk-checkin.o
 LIB_OBJS += bundle.o

bloom.c

@@ -0,0 +1,276 @@
+#include "git-compat-util.h"
+#include "bloom.h"
+#include "diff.h"
+#include "diffcore.h"
+#include "revision.h"
+#include "hashmap.h"
+#include "commit-graph.h"
+#include "commit.h"
+
+define_commit_slab(bloom_filter_slab, struct bloom_filter);
+
+struct bloom_filter_slab bloom_filters;
+
+struct pathmap_hash_entry {
+    struct hashmap_entry entry;
+    const char path[FLEX_ARRAY];
+};
+
+static uint32_t rotate_left(uint32_t value, int32_t count)
+{
+	uint32_t mask = 8 * sizeof(uint32_t) - 1;
+	count &= mask;
+	return ((value << count) | (value >> ((-count) & mask)));
+}
+
+static inline unsigned char get_bitmask(uint32_t pos)
+{
+	return ((unsigned char)1) << (pos & (BITS_PER_WORD - 1));
+}
+
+static int load_bloom_filter_from_graph(struct commit_graph *g,
+				   struct bloom_filter *filter,
+				   struct commit *c)
+{
+	uint32_t lex_pos, start_index, end_index;
+
+	while (c->graph_pos < g->num_commits_in_base)
+		g = g->base_graph;
+
+	/* The commit graph commit 'c' lives in doesn't carry bloom filters. */
+	if (!g->chunk_bloom_indexes)
+		return 0;
+
+	lex_pos = c->graph_pos - g->num_commits_in_base;
+
+	end_index = get_be32(g->chunk_bloom_indexes + 4 * lex_pos);
+
+	if (lex_pos > 0)
+		start_index = get_be32(g->chunk_bloom_indexes + 4 * (lex_pos - 1));
+	else
+		start_index = 0;
+
+	filter->len = end_index - start_index;
+	filter->data = (unsigned char *)(g->chunk_bloom_data +
+					sizeof(unsigned char) * start_index +
+					BLOOMDATA_CHUNK_HEADER_SIZE);
+
+	return 1;
+}
+
+/*
+ * Calculate the murmur3 32-bit hash value for the given data
+ * using the given seed.
+ * Produces a uniformly distributed hash value.
+ * Not considered to be cryptographically secure.
+ * Implemented as described in https://en.wikipedia.org/wiki/MurmurHash#Algorithm
+ */
+uint32_t murmur3_seeded(uint32_t seed, const char *data, size_t len)
+{
+	const uint32_t c1 = 0xcc9e2d51;
+	const uint32_t c2 = 0x1b873593;
+	const uint32_t r1 = 15;
+	const uint32_t r2 = 13;
+	const uint32_t m = 5;
+	const uint32_t n = 0xe6546b64;
+	int i;
+	uint32_t k1 = 0;
+	const char *tail;
+
+	int len4 = len / sizeof(uint32_t);
+
+	uint32_t k;
+	for (i = 0; i < len4; i++) {
+		uint32_t byte1 = (uint32_t)data[4*i];
+		uint32_t byte2 = ((uint32_t)data[4*i + 1]) << 8;
+		uint32_t byte3 = ((uint32_t)data[4*i + 2]) << 16;
+		uint32_t byte4 = ((uint32_t)data[4*i + 3]) << 24;
+		k = byte1 | byte2 | byte3 | byte4;
+		k *= c1;
+		k = rotate_left(k, r1);
+		k *= c2;
+
+		seed ^= k;
+		seed = rotate_left(seed, r2) * m + n;
+	}
+
+	tail = (data + len4 * sizeof(uint32_t));
+
+	switch (len & (sizeof(uint32_t) - 1)) {
+	case 3:
+		k1 ^= ((uint32_t)tail[2]) << 16;
+		/*-fallthrough*/
+	case 2:
+		k1 ^= ((uint32_t)tail[1]) << 8;
+		/*-fallthrough*/
+	case 1:
+		k1 ^= ((uint32_t)tail[0]) << 0;
+		k1 *= c1;
+		k1 = rotate_left(k1, r1);
+		k1 *= c2;
+		seed ^= k1;
+		break;
+	}
+
+	seed ^= (uint32_t)len;
+	seed ^= (seed >> 16);
+	seed *= 0x85ebca6b;
+	seed ^= (seed >> 13);
+	seed *= 0xc2b2ae35;
+	seed ^= (seed >> 16);
+
+	return seed;
+}
+
+void fill_bloom_key(const char *data,
+					size_t len,
+					struct bloom_key *key,
+					const struct bloom_filter_settings *settings)
+{
+	int i;
+	const uint32_t seed0 = 0x293ae76f;
+	const uint32_t seed1 = 0x7e646e2c;
+	const uint32_t hash0 = murmur3_seeded(seed0, data, len);
+	const uint32_t hash1 = murmur3_seeded(seed1, data, len);
+
+	key->hashes = (uint32_t *)xcalloc(settings->num_hashes, sizeof(uint32_t));
+	for (i = 0; i < settings->num_hashes; i++)
+		key->hashes[i] = hash0 + i * hash1;
+}
+
+void add_key_to_filter(const struct bloom_key *key,
+					   struct bloom_filter *filter,
+					   const struct bloom_filter_settings *settings)
+{
+	int i;
+	uint64_t mod = filter->len * BITS_PER_WORD;
+
+	for (i = 0; i < settings->num_hashes; i++) {
+		uint64_t hash_mod = key->hashes[i] % mod;
+		uint64_t block_pos = hash_mod / BITS_PER_WORD;
+
+		filter->data[block_pos] |= get_bitmask(hash_mod);
+	}
+}
+
+void init_bloom_filters(void)
+{
+	init_bloom_filter_slab(&bloom_filters);
+}
+
+struct bloom_filter *get_bloom_filter(struct repository *r,
+				      struct commit *c,
+					  int compute_if_not_present)
+{
+	struct bloom_filter *filter;
+	struct bloom_filter_settings settings = DEFAULT_BLOOM_FILTER_SETTINGS;
+	int i;
+	struct diff_options diffopt;
+	int max_changes = 512;
+
+	if (bloom_filters.slab_size == 0)
+		return NULL;
+
+	filter = bloom_filter_slab_at(&bloom_filters, c);
+
+	if (!filter->data) {
+		load_commit_graph_info(r, c);
+		if (c->graph_pos != COMMIT_NOT_FROM_GRAPH &&
+			r->objects->commit_graph->chunk_bloom_indexes) {
+			if (load_bloom_filter_from_graph(r->objects->commit_graph, filter, c))
+				return filter;
+			else
+				return NULL;
+		}
+	}
+
+	if (filter->data || !compute_if_not_present)
+		return filter;
+
+	repo_diff_setup(r, &diffopt);
+	diffopt.flags.recursive = 1;
+	diffopt.detect_rename = 0;
+	diffopt.max_changes = max_changes;
+	diff_setup_done(&diffopt);
+
+	if (c->parents)
+		diff_tree_oid(&c->parents->item->object.oid, &c->object.oid, "", &diffopt);
+	else
+		diff_tree_oid(NULL, &c->object.oid, "", &diffopt);
+	diffcore_std(&diffopt);
+
+	if (diff_queued_diff.nr <= max_changes) {
+		struct hashmap pathmap;
+		struct pathmap_hash_entry *e;
+		struct hashmap_iter iter;
+		hashmap_init(&pathmap, NULL, NULL, 0);
+
+		for (i = 0; i < diff_queued_diff.nr; i++) {
+			const char *path = diff_queued_diff.queue[i]->two->path;
+
+			/*
+			* Add each leading directory of the changed file, i.e. for
+			* 'dir/subdir/file' add 'dir' and 'dir/subdir' as well, so
+			* the Bloom filter could be used to speed up commands like
+			* 'git log dir/subdir', too.
+			*
+			* Note that directories are added without the trailing '/'.
+			*/
+			do {
+				char *last_slash = strrchr(path, '/');
+
+				FLEX_ALLOC_STR(e, path, path);
+				hashmap_entry_init(&e->entry, strhash(path));
+				hashmap_add(&pathmap, &e->entry);
+
+				if (!last_slash)
+					last_slash = (char*)path;
+				*last_slash = '\0';
+
+			} while (*path);
+
+			diff_free_filepair(diff_queued_diff.queue[i]);
+		}
+
+		filter->len = (hashmap_get_size(&pathmap) * settings.bits_per_entry + BITS_PER_WORD - 1) / BITS_PER_WORD;
+		filter->data = xcalloc(filter->len, sizeof(unsigned char));
+
+		hashmap_for_each_entry(&pathmap, &iter, e, entry) {
+			struct bloom_key key;
+			fill_bloom_key(e->path, strlen(e->path), &key, &settings);
+			add_key_to_filter(&key, filter, &settings);
+		}
+
+		hashmap_free_entries(&pathmap, struct pathmap_hash_entry, entry);
+	} else {
+		for (i = 0; i < diff_queued_diff.nr; i++)
+			diff_free_filepair(diff_queued_diff.queue[i]);
+		filter->data = NULL;
+		filter->len = 0;
+	}
+
+	free(diff_queued_diff.queue);
+	DIFF_QUEUE_CLEAR(&diff_queued_diff);
+
+	return filter;
+}
+
+int bloom_filter_contains(const struct bloom_filter *filter,
+			  const struct bloom_key *key,
+			  const struct bloom_filter_settings *settings)
+{
+	int i;
+	uint64_t mod = filter->len * BITS_PER_WORD;
+
+	if (!mod)
+		return -1;
+
+	for (i = 0; i < settings->num_hashes; i++) {
+		uint64_t hash_mod = key->hashes[i] % mod;
+		uint64_t block_pos = hash_mod / BITS_PER_WORD;
+		if (!(filter->data[block_pos] & get_bitmask(hash_mod)))
+			return 0;
+	}
+
+	return 1;
+}

bloom.h

@@ -0,0 +1,90 @@
+#ifndef BLOOM_H
+#define BLOOM_H
+
+struct commit;
+struct repository;
+
+struct bloom_filter_settings {
+	/*
+	 * The version of the hashing technique being used.
+	 * We currently only support version = 1 which is
+	 * the seeded murmur3 hashing technique implemented
+	 * in bloom.c.
+	 */
+	uint32_t hash_version;
+
+	/*
+	 * The number of times a path is hashed, i.e. the
+	 * number of bit positions tht cumulatively
+	 * determine whether a path is present in the
+	 * Bloom filter.
+	 */
+	uint32_t num_hashes;
+
+	/*
+	 * The minimum number of bits per entry in the Bloom
+	 * filter. If the filter contains 'n' entries, then
+	 * filter size is the minimum number of 8-bit words
+	 * that contain n*b bits.
+	 */
+	uint32_t bits_per_entry;
+};
+
+#define DEFAULT_BLOOM_FILTER_SETTINGS { 1, 7, 10 }
+#define BITS_PER_WORD 8
+#define BLOOMDATA_CHUNK_HEADER_SIZE 3 * sizeof(uint32_t)
+
+/*
+ * A bloom_filter struct represents a data segment to
+ * use when testing hash values. The 'len' member
+ * dictates how many entries are stored in
+ * 'data'.
+ */
+struct bloom_filter {
+	unsigned char *data;
+	size_t len;
+};
+
+/*
+ * A bloom_key represents the k hash values for a
+ * given string. These can be precomputed and
+ * stored in a bloom_key for re-use when testing
+ * against a bloom_filter. The number of hashes is
+ * given by the Bloom filter settings and is the same
+ * for all Bloom filters and keys interacting with
+ * the loaded version of the commit graph file and
+ * the Bloom data chunks.
+ */
+struct bloom_key {
+	uint32_t *hashes;
+};
+
+/*
+ * Calculate the murmur3 32-bit hash value for the given data
+ * using the given seed.
+ * Produces a uniformly distributed hash value.
+ * Not considered to be cryptographically secure.
+ * Implemented as described in https://en.wikipedia.org/wiki/MurmurHash#Algorithm
+ */
+uint32_t murmur3_seeded(uint32_t seed, const char *data, size_t len);
+
+void fill_bloom_key(const char *data,
+		    size_t len,
+		    struct bloom_key *key,
+		    const struct bloom_filter_settings *settings);
+
+void add_key_to_filter(const struct bloom_key *key,
+					   struct bloom_filter *filter,
+					   const struct bloom_filter_settings *settings);
+
+void init_bloom_filters(void);
+
+struct bloom_filter *get_bloom_filter(struct repository *r,
+				      struct commit *c,
+				      int compute_if_not_present);
+
+int bloom_filter_contains(const struct bloom_filter *filter,
+			  const struct bloom_key *key,
+			  const struct bloom_filter_settings *settings);
+
+#endif

builtin/commit-graph.c

@@ -11,7 +11,7 @@ static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph verify [--object-dir <objdir>] [--shallow] [--[no-]progress]"),
 	N_("git commit-graph write [--object-dir <objdir>] [--append] "
 	   "[--split[=<strategy>]] [--reachable|--stdin-packs|--stdin-commits] "
-	   "[--[no-]progress] <split options>"),
+	   "[--changed-paths] [--[no-]progress] <split options>"),
 	NULL
 };
 
@@ -23,7 +23,7 @@ static const char * const builtin_commit_graph_verify_usage[] = {
 static const char * const builtin_commit_graph_write_usage[] = {
 	N_("git commit-graph write [--object-dir <objdir>] [--append] "
 	   "[--split[=<strategy>]] [--reachable|--stdin-packs|--stdin-commits] "
-	   "[--[no-]progress] <split options>"),
+	   "[--changed-paths] [--[no-]progress] <split options>"),
 	NULL
 };
 
@@ -36,6 +36,7 @@ static struct opts_commit_graph {
 	int split;
 	int shallow;
 	int progress;
+	int enable_changed_paths;
 } opts;
 
 static struct object_directory *find_odb(struct repository *r,
@@ -158,6 +159,8 @@ static int graph_write(int argc, const char **argv)
 			N_("start walk at commits listed by stdin")),
 		OPT_BOOL(0, "append", &opts.append,
 			N_("include all commits already in the commit-graph file")),
+		OPT_BOOL(0, "changed-paths", &opts.enable_changed_paths,
+			N_("enable computation for changed paths")),
 		OPT_BOOL(0, "progress", &opts.progress, N_("force progress reporting")),
 		OPT_CALLBACK_F(0, "split", &split_opts.flags, NULL,
 			N_("allow writing an incremental commit-graph file"),
@@ -193,6 +196,9 @@ static int graph_write(int argc, const char **argv)
 		flags |= COMMIT_GRAPH_WRITE_SPLIT;
 	if (opts.progress)
 		flags |= COMMIT_GRAPH_WRITE_PROGRESS;
+	if (opts.enable_changed_paths ||
+	    git_env_bool(GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS, 0))
+		flags |= COMMIT_GRAPH_WRITE_BLOOM_FILTERS;
 
 	read_replace_refs = 0;
 	odb = find_odb(the_repository, opts.obj_dir);

ci/run-build-and-tests.sh

@@ -19,6 +19,7 @@ linux-gcc)
 	export GIT_TEST_OE_SIZE=10
 	export GIT_TEST_OE_DELTA_SIZE=5
 	export GIT_TEST_COMMIT_GRAPH=1
+	export GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=1
 	export GIT_TEST_MULTI_PACK_INDEX=1
 	export GIT_TEST_ADD_I_USE_BUILTIN=1
 	make test

commit-graph.c

@@ -16,13 +16,18 @@
 #include "hashmap.h"
 #include "replace-object.h"
 #include "progress.h"
+#include "bloom.h"
+#include "commit-slab.h"
 
 #define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
 #define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
 #define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
 #define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
 #define GRAPH_CHUNKID_EXTRAEDGES 0x45444745 /* "EDGE" */
+#define GRAPH_CHUNKID_BLOOMINDEXES 0x42494458 /* "BIDX" */
+#define GRAPH_CHUNKID_BLOOMDATA 0x42444154 /* "BDAT" */
 #define GRAPH_CHUNKID_BASE 0x42415345 /* "BASE" */
+#define MAX_NUM_CHUNKS 7
 
 #define GRAPH_DATA_WIDTH (the_hash_algo->rawsz + 16)
 
@@ -44,9 +49,51 @@
 /* Remember to update object flag allocation in object.h */
 #define REACHABLE       (1u<<15)
 
-char *get_commit_graph_filename(struct object_directory *odb)
+/* Keep track of the order in which commits are added to our list. */
+define_commit_slab(commit_pos, int);
+static struct commit_pos commit_pos = COMMIT_SLAB_INIT(1, commit_pos);
+
+static void set_commit_pos(struct repository *r, const struct object_id *oid)
+{
+	static int32_t max_pos;
+	struct commit *commit = lookup_commit(r, oid);
+
+	if (!commit)
+		return; /* should never happen, but be lenient */
+
+	*commit_pos_at(&commit_pos, commit) = max_pos++;
+}
+
+static int commit_pos_cmp(const void *va, const void *vb)
+{
+	const struct commit *a = *(const struct commit **)va;
+	const struct commit *b = *(const struct commit **)vb;
+	return commit_pos_at(&commit_pos, a) -
+	       commit_pos_at(&commit_pos, b);
+}
+
+static int commit_gen_cmp(const void *va, const void *vb)
+{
+	const struct commit *a = *(const struct commit **)va;
+	const struct commit *b = *(const struct commit **)vb;
+
+	/* lower generation commits first */
+	if (a->generation < b->generation)
+		return -1;
+	else if (a->generation > b->generation)
+		return 1;
+
+	/* use date as a heuristic when generations are equal */
+	if (a->date < b->date)
+		return -1;
+	else if (a->date > b->date)
+		return 1;
+	return 0;
+}
+
+char *get_commit_graph_filename(struct object_directory *obj_dir)
 {
-	return xstrfmt("%s/info/commit-graph", odb->path);
+	return xstrfmt("%s/info/commit-graph", obj_dir->path);
 }
 
 static char *get_split_graph_filename(struct object_directory *odb,
@@ -270,6 +317,32 @@ struct commit_graph *parse_commit_graph(void *graph_map, size_t graph_size)
 				chunk_repeated = 1;
 			else
 				graph->chunk_base_graphs = data + chunk_offset;
+			break;
+
+		case GRAPH_CHUNKID_BLOOMINDEXES:
+			if (graph->chunk_bloom_indexes)
+				chunk_repeated = 1;
+			else
+				graph->chunk_bloom_indexes = data + chunk_offset;
+			break;
+
+		case GRAPH_CHUNKID_BLOOMDATA:
+			if (graph->chunk_bloom_data)
+				chunk_repeated = 1;
+			else {
+				uint32_t hash_version;
+				graph->chunk_bloom_data = data + chunk_offset;
+				hash_version = get_be32(data + chunk_offset);
+
+				if (hash_version != 1)
+					break;
+
+				graph->bloom_filter_settings = xmalloc(sizeof(struct bloom_filter_settings));
+				graph->bloom_filter_settings->hash_version = hash_version;
+				graph->bloom_filter_settings->num_hashes = get_be32(data + chunk_offset + 4);
+				graph->bloom_filter_settings->bits_per_entry = get_be32(data + chunk_offset + 8);
+			}
+			break;
 		}
 
 		if (chunk_repeated) {
@@ -288,6 +361,15 @@ struct commit_graph *parse_commit_graph(void *graph_map, size_t graph_size)
 		last_chunk_offset = chunk_offset;
 	}
 
+	if (graph->chunk_bloom_indexes && graph->chunk_bloom_data) {
+		init_bloom_filters();
+	} else {
+		/* We need both the bloom chunks to exist together. Else ignore the data */
+		graph->chunk_bloom_indexes = NULL;
+		graph->chunk_bloom_data = NULL;
+		graph->bloom_filter_settings = NULL;
+	}
+
 	hashcpy(graph->oid.hash, graph->data + graph->data_len - graph->hash_len);
 
 	if (verify_commit_graph_lite(graph)) {
@@ -784,9 +866,12 @@ struct write_commit_graph_context {
 	unsigned append:1,
 		 report_progress:1,
 		 split:1,
-		 check_oids:1;
+		 check_oids:1,
+		 changed_paths:1,
+		 order_by_pack:1;
 
 	const struct split_commit_graph_opts *split_opts;
+	size_t total_bloom_filter_data_size;
 };
 
 static void write_graph_chunk_fanout(struct hashfile *f,
@@ -982,6 +1067,59 @@ static void write_graph_chunk_extra_edges(struct hashfile *f,
 	}
 }
 
+static void write_graph_chunk_bloom_indexes(struct hashfile *f,
+					    struct write_commit_graph_context *ctx)
+{
+	struct commit **list = ctx->commits.list;
+	struct commit **last = ctx->commits.list + ctx->commits.nr;
+	uint32_t cur_pos = 0;
+	struct progress *progress = NULL;
+	int i = 0;
+
+	if (ctx->report_progress)
+		progress = start_delayed_progress(
+			_("Writing changed paths Bloom filters index"),
+			ctx->commits.nr);
+
+	while (list < last) {
+		struct bloom_filter *filter = get_bloom_filter(ctx->r, *list, 0);
+		cur_pos += filter->len;
+		display_progress(progress, ++i);
+		hashwrite_be32(f, cur_pos);
+		list++;
+	}
+
+	stop_progress(&progress);
+}
+
+static void write_graph_chunk_bloom_data(struct hashfile *f,
+					 struct write_commit_graph_context *ctx,
+					 const struct bloom_filter_settings *settings)
+{
+	struct commit **list = ctx->commits.list;
+	struct commit **last = ctx->commits.list + ctx->commits.nr;
+	struct progress *progress = NULL;
+	int i = 0;
+
+	if (ctx->report_progress)
+		progress = start_delayed_progress(
+			_("Writing changed paths Bloom filters data"),
+			ctx->commits.nr);
+
+	hashwrite_be32(f, settings->hash_version);
+	hashwrite_be32(f, settings->num_hashes);
+	hashwrite_be32(f, settings->bits_per_entry);
+
+	while (list < last) {
+		struct bloom_filter *filter = get_bloom_filter(ctx->r, *list, 0);
+		display_progress(progress, ++i);
+		hashwrite(f, filter->data, filter->len * sizeof(unsigned char));
+		list++;
+	}
+
+	stop_progress(&progress);
+}
+
 static int oid_compare(const void *_a, const void *_b)
 {
 	const struct object_id *a = (const struct object_id *)_a;
@@ -1013,6 +1151,8 @@ static int add_packed_commits(const struct object_id *oid,
 	oidcpy(&(ctx->oids.list[ctx->oids.nr]), oid);
 	ctx->oids.nr++;
 
+	set_commit_pos(ctx->r, oid);
+
 	return 0;
 }
 
@@ -1132,6 +1272,38 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
 	stop_progress(&ctx->progress);
 }
 
+static void compute_bloom_filters(struct write_commit_graph_context *ctx)
+{
+	int i;
+	struct progress *progress = NULL;
+	struct commit **sorted_commits;
+
+	init_bloom_filters();
+
+	if (ctx->report_progress)
+		progress = start_delayed_progress(
+			_("Computing commit changed paths Bloom filters"),
+			ctx->commits.nr);
+
+	ALLOC_ARRAY(sorted_commits, ctx->commits.nr);
+	COPY_ARRAY(sorted_commits, ctx->commits.list, ctx->commits.nr);
+
+	if (ctx->order_by_pack)
+		QSORT(sorted_commits, ctx->commits.nr, commit_pos_cmp);
+	else
+		QSORT(sorted_commits, ctx->commits.nr, commit_gen_cmp);
+
+	for (i = 0; i < ctx->commits.nr; i++) {
+		struct commit *c = sorted_commits[i];
+		struct bloom_filter *filter = get_bloom_filter(ctx->r, c, 1);
+		ctx->total_bloom_filter_data_size += sizeof(unsigned char) * filter->len;
+		display_progress(progress, i + 1);
+	}
+
+	free(sorted_commits);
+	stop_progress(&progress);
+}
+
 static int add_ref_to_set(const char *refname,
 			  const struct object_id *oid,
 			  int flags, void *cb_data)
@@ -1361,12 +1533,13 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 	int fd;
 	struct hashfile *f;
 	struct lock_file lk = LOCK_INIT;
-	uint32_t chunk_ids[6];
-	uint64_t chunk_offsets[6];
+	uint32_t chunk_ids[MAX_NUM_CHUNKS + 1];
+	uint64_t chunk_offsets[MAX_NUM_CHUNKS + 1];
 	const unsigned hashsz = the_hash_algo->rawsz;
 	struct strbuf progress_title = STRBUF_INIT;
 	int num_chunks = 3;
 	struct object_id file_hash;
+	const struct bloom_filter_settings bloom_settings = DEFAULT_BLOOM_FILTER_SETTINGS;
 
 	if (ctx->split) {
 		struct strbuf tmp_file = STRBUF_INIT;
@@ -1411,6 +1584,12 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 		chunk_ids[num_chunks] = GRAPH_CHUNKID_EXTRAEDGES;
 		num_chunks++;
 	}
+	if (ctx->changed_paths) {
+		chunk_ids[num_chunks] = GRAPH_CHUNKID_BLOOMINDEXES;
+		num_chunks++;
+		chunk_ids[num_chunks] = GRAPH_CHUNKID_BLOOMDATA;
+		num_chunks++;
+	}
 	if (ctx->num_commit_graphs_after > 1) {
 		chunk_ids[num_chunks] = GRAPH_CHUNKID_BASE;
 		num_chunks++;
@@ -1429,6 +1608,15 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 						4 * ctx->num_extra_edges;
 		num_chunks++;
 	}
+	if (ctx->changed_paths) {
+		chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
+						sizeof(uint32_t) * ctx->commits.nr;
+		num_chunks++;
+
+		chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
+						sizeof(uint32_t) * 3 + ctx->total_bloom_filter_data_size;
+		num_chunks++;
+	}
 	if (ctx->num_commit_graphs_after > 1) {
 		chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
 						hashsz * (ctx->num_commit_graphs_after - 1);
@@ -1466,6 +1654,10 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 	write_graph_chunk_data(f, hashsz, ctx);
 	if (ctx->num_extra_edges)
 		write_graph_chunk_extra_edges(f, ctx);
+	if (ctx->changed_paths) {
+		write_graph_chunk_bloom_indexes(f, ctx);
+		write_graph_chunk_bloom_data(f, ctx, &bloom_settings);
+	}
 	if (ctx->num_commit_graphs_after > 1 &&
 	    write_graph_chunk_base(f, ctx)) {
 		return -1;
@@ -1804,6 +1996,8 @@ int write_commit_graph(struct object_directory *odb,
 	ctx->split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0;
 	ctx->check_oids = flags & COMMIT_GRAPH_WRITE_CHECK_OIDS ? 1 : 0;
 	ctx->split_opts = split_opts;
+	ctx->changed_paths = flags & COMMIT_GRAPH_WRITE_BLOOM_FILTERS ? 1 : 0;
+	ctx->total_bloom_filter_data_size = 0;
 
 	if (ctx->split) {
 		struct commit_graph *g;
@@ -1856,6 +2050,7 @@ int write_commit_graph(struct object_directory *odb,
 	}
 
 	if (pack_indexes) {
+		ctx->order_by_pack = 1;
 		if ((res = fill_oids_from_packs(ctx, pack_indexes)))
 			goto cleanup;
 	}
@@ -1865,8 +2060,10 @@ int write_commit_graph(struct object_directory *odb,
 			goto cleanup;
 	}
 
-	if (!pack_indexes && !commits)
+	if (!pack_indexes && !commits) {
+		ctx->order_by_pack = 1;
 		fill_oids_from_all_packs(ctx);
+	}
 
 	close_reachable(ctx);
 
@@ -1902,6 +2099,9 @@ int write_commit_graph(struct object_directory *odb,
 
 	compute_generation_numbers(ctx);
 
+	if (ctx->changed_paths)
+		compute_bloom_filters(ctx);
+
 	res = write_commit_graph_file(ctx);
 
 	if (ctx->split)
@@ -2126,6 +2326,7 @@ void free_commit_graph(struct commit_graph *g)
 		g->data = NULL;
 	}
 	free(g->filename);
+	free(g->bloom_filter_settings);
 	free(g);
 }
 

commit-graph.h

@@ -10,8 +10,10 @@
 
 #define GIT_TEST_COMMIT_GRAPH "GIT_TEST_COMMIT_GRAPH"
 #define GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD "GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD"
+#define GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS "GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS"
 
 struct commit;
+struct bloom_filter_settings;
 
 char *get_commit_graph_filename(struct object_directory *odb);
 int open_commit_graph(const char *graph_file, int *fd, struct stat *st);
@@ -58,6 +60,10 @@ struct commit_graph {
 	const unsigned char *chunk_commit_data;
 	const unsigned char *chunk_extra_edges;
 	const unsigned char *chunk_base_graphs;
+	const unsigned char *chunk_bloom_indexes;
+	const unsigned char *chunk_bloom_data;
+
+	struct bloom_filter_settings *bloom_filter_settings;
 };
 
 struct commit_graph *load_commit_graph_one_fd_st(int fd, struct stat *st,
@@ -77,7 +83,8 @@ enum commit_graph_write_flags {
 	COMMIT_GRAPH_WRITE_PROGRESS   = (1 << 1),
 	COMMIT_GRAPH_WRITE_SPLIT      = (1 << 2),
 	/* Make sure that each OID in the input is a valid commit OID. */
-	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3)
+	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3),
+	COMMIT_GRAPH_WRITE_BLOOM_FILTERS = (1 << 4),
 };
 
 enum commit_graph_split_flags {

diff.h

@@ -285,6 +285,11 @@ struct diff_options {
 	/* Number of hexdigits to abbreviate raw format output to. */
 	int abbrev;
 
+	/* If non-zero, then stop computing after this many changes. */
+	int max_changes;
+	/* For internal use only. */
+	int num_changes;
+
 	int ita_invisible_in_index;
 /* white-space error highlighting */
 #define WSEH_NEW (1<<12)

revision.c

@@ -29,6 +29,8 @@
 #include "prio-queue.h"
 #include "hashmap.h"
 #include "utf8.h"
+#include "bloom.h"
+#include "json-writer.h"
 
 volatile show_early_output_fn_t show_early_output;
 
@@ -624,11 +626,116 @@ static void file_change(struct diff_options *options,
 	options->flags.has_changes = 1;
 }
 
+static int bloom_filter_atexit_registered;
+static unsigned int count_bloom_filter_maybe;
+static unsigned int count_bloom_filter_definitely_not;
+static unsigned int count_bloom_filter_false_positive;
+static unsigned int count_bloom_filter_not_present;
+static unsigned int count_bloom_filter_length_zero;
+
+static void trace2_bloom_filter_statistics_atexit(void)
+{
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	jw_object_intmax(&jw, "filter_not_present", count_bloom_filter_not_present);
+	jw_object_intmax(&jw, "zero_length_filter", count_bloom_filter_length_zero);
+	jw_object_intmax(&jw, "maybe", count_bloom_filter_maybe);
+	jw_object_intmax(&jw, "definitely_not", count_bloom_filter_definitely_not);
+	jw_object_intmax(&jw, "false_positive", count_bloom_filter_false_positive);
+	jw_end(&jw);
+
+	trace2_data_json("bloom", the_repository, "statistics", &jw);
+
+	jw_release(&jw);
+}
+
+static void prepare_to_use_bloom_filter(struct rev_info *revs)
+{
+	struct pathspec_item *pi;
+	char *path_alloc = NULL;
+	const char *path;
+	int last_index;
+	int len;
+
+	if (!revs->commits)
+	    return;
+
+	repo_parse_commit(revs->repo, revs->commits->item);
+
+	if (!revs->repo->objects->commit_graph)
+		return;
+
+	revs->bloom_filter_settings = revs->repo->objects->commit_graph->bloom_filter_settings;
+	if (!revs->bloom_filter_settings)
+		return;
+
+	pi = &revs->pruning.pathspec.items[0];
+	last_index = pi->len - 1;
+
+	/* remove single trailing slash from path, if needed */
+	if (pi->match[last_index] == '/') {
+	    path_alloc = xstrdup(pi->match);
+	    path_alloc[last_index] = '\0';
+	    path = path_alloc;
+	} else
+	    path = pi->match;
+
+	len = strlen(path);
+
+	revs->bloom_key = xmalloc(sizeof(struct bloom_key));
+	fill_bloom_key(path, len, revs->bloom_key, revs->bloom_filter_settings);
+
+	if (trace2_is_enabled() && !bloom_filter_atexit_registered) {
+		atexit(trace2_bloom_filter_statistics_atexit);
+		bloom_filter_atexit_registered = 1;
+	}
+
+	free(path_alloc);
+}
+
+static int check_maybe_different_in_bloom_filter(struct rev_info *revs,
+						 struct commit *commit)
+{
+	struct bloom_filter *filter;
+	int result;
+
+	if (!revs->repo->objects->commit_graph)
+		return -1;
+
+	if (commit->generation == GENERATION_NUMBER_INFINITY)
+		return -1;
+
+	filter = get_bloom_filter(revs->repo, commit, 0);
+
+	if (!filter) {
+		count_bloom_filter_not_present++;
+		return -1;
+	}
+
+	if (!filter->len) {
+		count_bloom_filter_length_zero++;
+		return -1;
+	}
+
+	result = bloom_filter_contains(filter,
+				       revs->bloom_key,
+				       revs->bloom_filter_settings);
+
+	if (result)
+		count_bloom_filter_maybe++;
+	else
+		count_bloom_filter_definitely_not++;
+
+	return result;
+}
+
 static int rev_compare_tree(struct rev_info *revs,
-			    struct commit *parent, struct commit *commit)
+			    struct commit *parent, struct commit *commit, int nth_parent)
 {
 	struct tree *t1 = get_commit_tree(parent);
 	struct tree *t2 = get_commit_tree(commit);
+	int bloom_ret = 1;
 
 	if (!t1)
 		return REV_TREE_NEW;
@@ -653,11 +760,23 @@ static int rev_compare_tree(struct rev_info *revs,
 			return REV_TREE_SAME;
 	}
 
+	if (revs->bloom_key && !nth_parent) {
+		bloom_ret = check_maybe_different_in_bloom_filter(revs, commit);
+
+		if (bloom_ret == 0)
+			return REV_TREE_SAME;
+	}
+
 	tree_difference = REV_TREE_SAME;
 	revs->pruning.flags.has_changes = 0;
 	if (diff_tree_oid(&t1->object.oid, &t2->object.oid, "",
 			   &revs->pruning) < 0)
 		return REV_TREE_DIFFERENT;
+
+	if (!nth_parent)
+		if (bloom_ret == 1 && tree_difference == REV_TREE_SAME)
+			count_bloom_filter_false_positive++;
+
 	return tree_difference;
 }
 
@@ -855,7 +974,7 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
 			die("cannot simplify commit %s (because of %s)",
 			    oid_to_hex(&commit->object.oid),
 			    oid_to_hex(&p->object.oid));
-		switch (rev_compare_tree(revs, p, commit)) {
+		switch (rev_compare_tree(revs, p, commit, nth_parent)) {
 		case REV_TREE_SAME:
 			if (!revs->simplify_history || !relevant_commit(p)) {
 				/* Even if a merge with an uninteresting
@@ -3385,6 +3504,8 @@ int prepare_revision_walk(struct rev_info *revs)
 				       FOR_EACH_OBJECT_PROMISOR_ONLY);
 	}
 
+	if (revs->pruning.pathspec.nr == 1 && !revs->reflog_info)
+		prepare_to_use_bloom_filter(revs);
 	if (revs->no_walk != REVISION_WALK_NO_WALK_UNSORTED)
 		commit_list_sort_by_date(&revs->commits);
 	if (revs->no_walk)
@@ -3402,6 +3523,7 @@ int prepare_revision_walk(struct rev_info *revs)
 		simplify_merges(revs);
 	if (revs->children.name)
 		set_children(revs);
+
 	return 0;
 }
 

revision.h

@@ -59,6 +59,8 @@ struct repository;
 struct rev_info;
 struct string_list;
 struct saved_parents;
+struct bloom_key;
+struct bloom_filter_settings;
 define_shared_commit_slab(revision_sources, char *);
 
 struct rev_cmdline_info {
@@ -296,6 +298,15 @@ struct rev_info {
 	struct revision_sources *sources;
 
 	struct topo_walk_info *topo_walk_info;
+
+	/* Commit graph bloom filter fields */
+	/* The bloom filter key for the pathspec */
+	struct bloom_key *bloom_key;
+	/*
+	 * The bloom filter settings used to generate the key.
+	 * This is loaded from the commit-graph being used.
+	 */
+	struct bloom_filter_settings *bloom_filter_settings;
 };
 
 int ref_excluded(struct string_list *, const char *path);

t/README

@@ -379,6 +379,11 @@ GIT_TEST_COMMIT_GRAPH=<boolean>, when true, forces the commit-graph to
 be written after every 'git commit' command, and overrides the
 'core.commitGraph' setting to true.
 
+GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=<boolean>, when true, forces
+commit-graph write to compute and write changed path Bloom filters for
+every 'git commit-graph write', as if the `--changed-paths` option was
+passed in.
+
 GIT_TEST_FSMONITOR=$PWD/t7519/fsmonitor-all exercises the fsmonitor
 code path for utilizing a file system monitor to speed up detecting
 new or changed files.

t/helper/test-bloom.c

@@ -0,0 +1,81 @@
+#include "git-compat-util.h"
+#include "bloom.h"
+#include "test-tool.h"
+#include "commit.h"
+
+struct bloom_filter_settings settings = DEFAULT_BLOOM_FILTER_SETTINGS;
+
+static void add_string_to_filter(const char *data, struct bloom_filter *filter) {
+		struct bloom_key key;
+		int i;
+
+		fill_bloom_key(data, strlen(data), &key, &settings);
+		printf("Hashes:");
+		for (i = 0; i < settings.num_hashes; i++){
+			printf("0x%08x|", key.hashes[i]);
+		}
+		printf("\n");
+		add_key_to_filter(&key, filter, &settings);
+}
+
+static void print_bloom_filter(struct bloom_filter *filter) {
+	int i;
+
+	if (!filter) {
+		printf("No filter.\n");
+		return;
+	}
+	printf("Filter_Length:%d\n", (int)filter->len);
+	printf("Filter_Data:");
+	for (i = 0; i < filter->len; i++){
+		printf("%02x|", filter->data[i]);
+	}
+	printf("\n");
+}
+
+static void get_bloom_filter_for_commit(const struct object_id *commit_oid)
+{
+	struct commit *c;
+	struct bloom_filter *filter;
+	setup_git_directory();
+	c = lookup_commit(the_repository, commit_oid);
+	filter = get_bloom_filter(the_repository, c, 1);
+	print_bloom_filter(filter);
+}
+
+int cmd__bloom(int argc, const char **argv)
+{
+	if (!strcmp(argv[1], "get_murmur3")) {
+		uint32_t hashed = murmur3_seeded(0, argv[2], strlen(argv[2]));
+		printf("Murmur3 Hash with seed=0:0x%08x\n", hashed);
+	}
+
+    if (!strcmp(argv[1], "generate_filter")) {
+		struct bloom_filter filter;
+		int i = 2;
+		filter.len =  (settings.bits_per_entry + BITS_PER_WORD - 1) / BITS_PER_WORD;
+		filter.data = xcalloc(filter.len, sizeof(unsigned char));
+
+		if (!argv[2]){
+			die("at least one input string expected");
+		}
+
+		while (argv[i]) {
+			add_string_to_filter(argv[i], &filter);
+			i++;
+		}
+
+		print_bloom_filter(&filter);
+	}
+
+    if (!strcmp(argv[1], "get_filter_for_commit")) {
+		struct object_id oid;
+		const char *end;
+		if (parse_oid_hex(argv[2], &oid, &end))
+			die("cannot parse oid '%s'", argv[2]);
+		init_bloom_filters();
+		get_bloom_filter_for_commit(&oid);
+	}
+
+	return 0;
+}

t/helper/test-read-graph.c

@@ -34,6 +34,10 @@ int cmd__read_graph(int argc, const char **argv)
 		printf(" commit_metadata");
 	if (graph->chunk_extra_edges)
 		printf(" extra_edges");
+	if (graph->chunk_bloom_indexes)
+		printf(" bloom_indexes");
+	if (graph->chunk_bloom_data)
+		printf(" bloom_data");
 	printf("\n");
 
 	UNLEAK(graph);

t/helper/test-tool.c

@@ -15,6 +15,7 @@ struct test_cmd {
 
 static struct test_cmd cmds[] = {
 	{ "advise", cmd__advise_if_enabled },
+	{ "bloom", cmd__bloom },
 	{ "chmtime", cmd__chmtime },
 	{ "config", cmd__config },
 	{ "ctype", cmd__ctype },

t/helper/test-tool.h

@@ -5,6 +5,7 @@
 #include "git-compat-util.h"
 
 int cmd__advise_if_enabled(int argc, const char **argv);
+int cmd__bloom(int argc, const char **argv);
 int cmd__chmtime(int argc, const char **argv);
 int cmd__config(int argc, const char **argv);
 int cmd__ctype(int argc, const char **argv);

t/t0095-bloom.sh

@@ -0,0 +1,117 @@
+#!/bin/sh
+
+test_description='Testing the various Bloom filter computations in bloom.c'
+. ./test-lib.sh
+
+test_expect_success 'compute unseeded murmur3 hash for empty string' '
+	cat >expect <<-\EOF &&
+	Murmur3 Hash with seed=0:0x00000000
+	EOF
+	test-tool bloom get_murmur3 "" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'compute unseeded murmur3 hash for test string 1' '
+	cat >expect <<-\EOF &&
+	Murmur3 Hash with seed=0:0x627b0c2c
+	EOF
+	test-tool bloom get_murmur3 "Hello world!" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'compute unseeded murmur3 hash for test string 2' '
+	cat >expect <<-\EOF &&
+	Murmur3 Hash with seed=0:0x2e4ff723
+	EOF
+	test-tool bloom get_murmur3 "The quick brown fox jumps over the lazy dog" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'compute bloom key for empty string' '
+	cat >expect <<-\EOF &&
+	Hashes:0x5615800c|0x5b966560|0x61174ab4|0x66983008|0x6c19155c|0x7199fab0|0x771ae004|
+	Filter_Length:2
+	Filter_Data:11|11|
+	EOF
+	test-tool bloom generate_filter "" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'compute bloom key for whitespace' '
+	cat >expect <<-\EOF &&
+	Hashes:0xf178874c|0x5f3d6eb6|0xcd025620|0x3ac73d8a|0xa88c24f4|0x16510c5e|0x8415f3c8|
+	Filter_Length:2
+	Filter_Data:51|55|
+	EOF
+	test-tool bloom generate_filter " " >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'compute bloom key for test string 1' '
+	cat >expect <<-\EOF &&
+	Hashes:0xb270de9b|0x1bb6f26e|0x84fd0641|0xee431a14|0x57892de7|0xc0cf41ba|0x2a15558d|
+	Filter_Length:2
+	Filter_Data:92|6c|
+	EOF
+	test-tool bloom generate_filter "Hello world!" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'compute bloom key for test string 2' '
+	cat >expect <<-\EOF &&
+	Hashes:0x20ab385b|0xf5237fe2|0xc99bc769|0x9e140ef0|0x728c5677|0x47049dfe|0x1b7ce585|
+	Filter_Length:2
+	Filter_Data:a5|4a|
+	EOF
+	test-tool bloom generate_filter "file.txt" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'get bloom filters for commit with no changes' '
+	git init &&
+	git commit --allow-empty -m "c0" &&
+	cat >expect <<-\EOF &&
+	Filter_Length:0
+	Filter_Data:
+	EOF
+	test-tool bloom get_filter_for_commit "$(git rev-parse HEAD)" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'get bloom filter for commit with 10 changes' '
+	rm actual &&
+	rm expect &&
+	mkdir smallDir &&
+	for i in $(test_seq 0 9)
+	do
+		echo $i >smallDir/$i
+	done &&
+	git add smallDir &&
+	git commit -m "commit with 10 changes" &&
+	cat >expect <<-\EOF &&
+	Filter_Length:25
+	Filter_Data:82|a0|65|47|0c|92|90|c0|a1|40|02|a0|e2|40|e0|04|0a|9a|66|cf|80|19|85|42|23|
+	EOF
+	test-tool bloom get_filter_for_commit "$(git rev-parse HEAD)" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success EXPENSIVE 'get bloom filter for commit with 513 changes' '
+	rm actual &&
+	rm expect &&
+	mkdir bigDir &&
+	for i in $(test_seq 0 512)
+	do
+		echo $i >bigDir/$i
+	done &&
+	git add bigDir &&
+	git commit -m "commit with 513 changes" &&
+	cat >expect <<-\EOF &&
+	Filter_Length:0
+	Filter_Data:
+	EOF
+	test-tool bloom get_filter_for_commit "$(git rev-parse HEAD)" >actual &&
+	test_cmp expect actual
+'
+
+test_done

t/t4216-log-bloom.sh

@@ -0,0 +1,155 @@
+#!/bin/sh
+
+test_description='git log for a path with Bloom filters'
+. ./test-lib.sh
+
+GIT_TEST_COMMIT_GRAPH=0
+GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
+
+test_expect_success 'setup test - repo, commits, commit graph, log outputs' '
+	git init &&
+	mkdir A A/B A/B/C &&
+	test_commit c1 A/file1 &&
+	test_commit c2 A/B/file2 &&
+	test_commit c3 A/B/C/file3 &&
+	test_commit c4 A/file1 &&
+	test_commit c5 A/B/file2 &&
+	test_commit c6 A/B/C/file3 &&
+	test_commit c7 A/file1 &&
+	test_commit c8 A/B/file2 &&
+	test_commit c9 A/B/C/file3 &&
+	test_commit c10 file_to_be_deleted &&
+	git checkout -b side HEAD~4 &&
+	test_commit side-1 file4 &&
+	git checkout master &&
+	git merge side &&
+	test_commit c11 file5 &&
+	mv file5 file5_renamed &&
+	git add file5_renamed &&
+	git commit -m "rename" &&
+	rm file_to_be_deleted &&
+	git add . &&
+	git commit -m "file removed" &&
+	git commit-graph write --reachable --changed-paths
+'
+graph_read_expect () {
+	NUM_CHUNKS=5
+	cat >expect <<- EOF
+	header: 43475048 1 1 $NUM_CHUNKS 0
+	num_commits: $1
+	chunks: oid_fanout oid_lookup commit_metadata bloom_indexes bloom_data
+	EOF
+	test-tool read-graph >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'commit-graph write wrote out the bloom chunks' '
+	graph_read_expect 15
+'
+
+# Turn off any inherited trace2 settings for this test.
+sane_unset GIT_TRACE2 GIT_TRACE2_PERF GIT_TRACE2_EVENT
+sane_unset GIT_TRACE2_PERF_BRIEF
+sane_unset GIT_TRACE2_CONFIG_PARAMS
+
+setup () {
+	rm "$TRASH_DIRECTORY/trace.perf"
+	git -c core.commitGraph=false log --pretty="format:%s" $1 >log_wo_bloom &&
+	GIT_TRACE2_PERF="$TRASH_DIRECTORY/trace.perf" git -c core.commitGraph=true log --pretty="format:%s" $1 >log_w_bloom
+}
+
+test_bloom_filters_used () {
+	log_args=$1
+	bloom_trace_prefix="statistics:{\"filter_not_present\":0,\"zero_length_filter\":0,\"maybe\""
+	setup "$log_args" &&
+	grep -q "$bloom_trace_prefix" "$TRASH_DIRECTORY/trace.perf" &&
+	test_cmp log_wo_bloom log_w_bloom &&
+    test_path_is_file "$TRASH_DIRECTORY/trace.perf"
+}
+
+test_bloom_filters_not_used () {
+	log_args=$1
+	setup "$log_args" &&
+	!(grep -q "statistics:{\"filter_not_present\":" "$TRASH_DIRECTORY/trace.perf") &&
+	test_cmp log_wo_bloom log_w_bloom
+}
+
+for path in A A/B A/B/C A/file1 A/B/file2 A/B/C/file3 file4 file5 file5_renamed file_to_be_deleted
+do
+	for option in "" \
+	      "--all" \
+		      "--full-history" \
+		      "--full-history --simplify-merges" \
+		      "--simplify-merges" \
+		      "--simplify-by-decoration" \
+		      "--follow" \
+		      "--first-parent" \
+		      "--topo-order" \
+		      "--date-order" \
+		      "--author-date-order" \
+		      "--ancestry-path side..master"
+	do
+		test_expect_success "git log option: $option for path: $path" '
+			test_bloom_filters_used "$option -- $path"
+		'
+	done
+done
+
+test_expect_success 'git log -- folder works with and without the trailing slash' '
+	test_bloom_filters_used "-- A" &&
+	test_bloom_filters_used "-- A/"
+'
+
+test_expect_success 'git log for path that does not exist. ' '
+	test_bloom_filters_used "-- path_does_not_exist"
+'
+
+test_expect_success 'git log with --walk-reflogs does not use Bloom filters' '
+	test_bloom_filters_not_used "--walk-reflogs -- A"
+'
+
+test_expect_success 'git log -- multiple path specs does not use Bloom filters' '
+	test_bloom_filters_not_used "-- file4 A/file1"
+'
+
+test_expect_success 'git log with wildcard that resolves to a single path uses Bloom filters' '
+	test_bloom_filters_used "-- *4" &&
+	test_bloom_filters_used "-- *renamed"
+'
+
+test_expect_success 'git log with wildcard that resolves to a multiple paths does not uses Bloom filters' '
+	test_bloom_filters_not_used "-- *" &&
+	test_bloom_filters_not_used "-- file*"
+'
+
+test_expect_success 'setup - add commit-graph to the chain without Bloom filters' '
+	test_commit c14 A/anotherFile2 &&
+	test_commit c15 A/B/anotherFile2 &&
+	test_commit c16 A/B/C/anotherFile2 &&
+	GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0 git commit-graph write --reachable --split &&
+	test_line_count = 2 .git/objects/info/commit-graphs/commit-graph-chain
+'
+
+test_expect_success 'Do not use Bloom filters if the latest graph does not have Bloom filters.' '
+	test_bloom_filters_not_used "-- A/B"
+'
+
+test_expect_success 'setup - add commit-graph to the chain with Bloom filters' '
+	test_commit c17 A/anotherFile3 &&
+	git commit-graph write --reachable --changed-paths --split &&
+	test_line_count = 3 .git/objects/info/commit-graphs/commit-graph-chain
+'
+
+test_bloom_filters_used_when_some_filters_are_missing () {
+	log_args=$1
+	bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"zero_length_filter\":0,\"maybe\":8,\"definitely_not\":6"
+	setup "$log_args" &&
+	grep -q "$bloom_trace_prefix" "$TRASH_DIRECTORY/trace.perf" &&
+	test_cmp log_wo_bloom log_w_bloom
+}
+
+test_expect_success 'Use Bloom filters if they exist in the latest but not all commit graphs in the chain.' '
+	test_bloom_filters_used_when_some_filters_are_missing "-- A/B"
+'
+
+test_done

t/t5318-commit-graph.sh

@@ -3,6 +3,8 @@
 test_description='commit graph'
 . ./test-lib.sh
 
+GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
+
 test_expect_success 'setup full repo' '
 	mkdir full &&
 	cd "$TRASH_DIRECTORY/full" &&

t/t5324-split-commit-graph.sh

@@ -4,6 +4,7 @@ test_description='split commit graph'
 . ./test-lib.sh
 
 GIT_TEST_COMMIT_GRAPH=0
+GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
 
 test_expect_success 'setup repo' '
 	git init &&

tree-diff.c

@@ -434,6 +434,9 @@ static struct combine_diff_path *ll_diff_tree_paths(
 		if (diff_can_quit_early(opt))
 			break;
 
+		if (opt->max_changes && opt->num_changes > opt->max_changes)
+			break;
+
 		if (opt->pathspec.nr) {
 			skip_uninteresting(&t, base, opt);
 			for (i = 0; i < nparent; i++)
@@ -518,6 +521,7 @@ static struct combine_diff_path *ll_diff_tree_paths(
 
 			/* t↓ */
 			update_tree_entry(&t);
+			opt->num_changes++;
 		}
 
 		/* t > p[imin] */
@@ -535,6 +539,7 @@ static struct combine_diff_path *ll_diff_tree_paths(
 		skip_emit_tp:
 			/* ∀ pi=p[imin]  pi↓ */
 			update_tp_entries(tp, nparent);
+			opt->num_changes++;
 		}
 	}
 
@@ -552,6 +557,7 @@ struct combine_diff_path *diff_tree_paths(
 	const struct object_id **parents_oid, int nparent,
 	struct strbuf *base, struct diff_options *opt)
 {
+	opt->num_changes = 0;
 	p = ll_diff_tree_paths(p, oid, parents_oid, nparent, base, opt);
 
 	/*