diff mbox series

[v3,3/5] make object_directory.loose_objects_subdir_seen a bitmap

Message ID 20210707231019.14738-4-e@80x24.org (mailing list archive)
State Accepted
Commit 33f379eee63a0529f85079857598ac6325d3aec5
Headers show
Series [v3,1/5] speed up alt_odb_usable() with many alternates | expand

Commit Message

Eric Wong July 7, 2021, 11:10 p.m. UTC 
There's no point in using 8 bits per-directory when 1 bit
will do.  This saves us 224 bytes per object directory, which
ends up being 22MB when dealing with 100K alternates.

v2: use bitsizeof() macro and better variable names

Signed-off-by: Eric Wong <e@80x24.org>
---
 object-file.c  | 11 ++++++++---
 object-store.h |  2 +-
 2 files changed, 9 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/object-file.c b/object-file.c
index 2dd70ddf3a..91ded8c22a 100644
--- a/object-file.c
+++ b/object-file.c
@@ -2461,12 +2461,17 @@  struct oid_array *odb_loose_cache(struct object_directory *odb,
 {
 	int subdir_nr = oid->hash[0];
 	struct strbuf buf = STRBUF_INIT;
+	size_t word_bits = bitsizeof(odb->loose_objects_subdir_seen[0]);
+	size_t word_index = subdir_nr / word_bits;
+	size_t mask = 1 << (subdir_nr % word_bits);
+	uint32_t *bitmap;
 
 	if (subdir_nr < 0 ||
-	    subdir_nr >= ARRAY_SIZE(odb->loose_objects_subdir_seen))
+	    subdir_nr >= bitsizeof(odb->loose_objects_subdir_seen))
 		BUG("subdir_nr out of range");
 
-	if (odb->loose_objects_subdir_seen[subdir_nr])
+	bitmap = &odb->loose_objects_subdir_seen[word_index];
+	if (*bitmap & mask)
 		return &odb->loose_objects_cache[subdir_nr];
 
 	strbuf_addstr(&buf, odb->path);
@@ -2474,7 +2479,7 @@  struct oid_array *odb_loose_cache(struct object_directory *odb,
 				    append_loose_object,
 				    NULL, NULL,
 				    &odb->loose_objects_cache[subdir_nr]);
-	odb->loose_objects_subdir_seen[subdir_nr] = 1;
+	*bitmap |= mask;
 	strbuf_release(&buf);
 	return &odb->loose_objects_cache[subdir_nr];
 }
diff --git a/object-store.h b/object-store.h
index 6077065d90..ab6d469970 100644
--- a/object-store.h
+++ b/object-store.h
@@ -22,7 +22,7 @@  struct object_directory {
 	 *
 	 * Be sure to call odb_load_loose_cache() before using.
 	 */
-	char loose_objects_subdir_seen[256];
+	uint32_t loose_objects_subdir_seen[8]; /* 256 bits */
 	struct oid_array loose_objects_cache[256];
 
 	/*