oidtree: a crit-bit tree for odb_loose_cache
This saves 8K per `struct object_directory', meaning it saves
around 800MB in my case involving 100K alternates (half or more
of those alternates are unlikely to hold loose objects).
This is implemented in two parts: a generic, allocation-free
`cbtree' and the `oidtree' wrapper on top of it. The latter
provides allocation using alloc_state as a memory pool to
improve locality and reduce free(3) overhead.
Unlike oid-array, the crit-bit tree does not require sorting.
Performance is bound by the key length, for oidtree that is
fixed at sizeof(struct object_id). There's no need to have
256 oidtrees to mitigate the O(n log n) overhead like we did
with oid-array.
Being a prefix trie, it is natively suited for expanding short
object IDs via prefix-limited iteration in
`find_short_object_filename'.
On my busy workstation, p4205 performance seems to be roughly
unchanged (+/-8%). Startup with 100K total alternates with no
loose objects seems around 10-20% faster on a hot cache.
(800MB in memory savings means more memory for the kernel FS
cache).
The generic cbtree implementation does impose some extra
overhead for oidtree in that it uses memcmp(3) on
"struct object_id" so it wastes cycles comparing 12 extra bytes
on SHA-1 repositories. I've not yet explored reducing this
overhead, but I expect there are many places in our code base
where we'd want to investigate this.
More information on crit-bit trees: https://cr.yp.to/critbit.html
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/object-file.c b/object-file.c
index 91ded8c..35f3e7e 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1173,7 +1173,7 @@ static int quick_has_loose(struct repository *r,
prepare_alt_odb(r);
for (odb = r->objects->odb; odb; odb = odb->next) {
- if (oid_array_lookup(odb_loose_cache(odb, oid), oid) >= 0)
+ if (oidtree_contains(odb_loose_cache(odb, oid), oid))
return 1;
}
return 0;
@@ -2452,11 +2452,11 @@ int for_each_loose_object(each_loose_object_fn cb, void *data,
static int append_loose_object(const struct object_id *oid, const char *path,
void *data)
{
- oid_array_append(data, oid);
+ oidtree_insert(data, oid);
return 0;
}
-struct oid_array *odb_loose_cache(struct object_directory *odb,
+struct oidtree *odb_loose_cache(struct object_directory *odb,
const struct object_id *oid)
{
int subdir_nr = oid->hash[0];
@@ -2472,24 +2472,25 @@ struct oid_array *odb_loose_cache(struct object_directory *odb,
bitmap = &odb->loose_objects_subdir_seen[word_index];
if (*bitmap & mask)
- return &odb->loose_objects_cache[subdir_nr];
-
+ return odb->loose_objects_cache;
+ if (!odb->loose_objects_cache) {
+ ALLOC_ARRAY(odb->loose_objects_cache, 1);
+ oidtree_init(odb->loose_objects_cache);
+ }
strbuf_addstr(&buf, odb->path);
for_each_file_in_obj_subdir(subdir_nr, &buf,
append_loose_object,
NULL, NULL,
- &odb->loose_objects_cache[subdir_nr]);
+ odb->loose_objects_cache);
*bitmap |= mask;
strbuf_release(&buf);
- return &odb->loose_objects_cache[subdir_nr];
+ return odb->loose_objects_cache;
}
void odb_clear_loose_cache(struct object_directory *odb)
{
- int i;
-
- for (i = 0; i < ARRAY_SIZE(odb->loose_objects_cache); i++)
- oid_array_clear(&odb->loose_objects_cache[i]);
+ oidtree_clear(odb->loose_objects_cache);
+ FREE_AND_NULL(odb->loose_objects_cache);
memset(&odb->loose_objects_subdir_seen, 0,
sizeof(odb->loose_objects_subdir_seen));
}
