From: Han Xin <hanxin.hx@xxxxxxxxxxxxxxx>
We used to call "get_data()" in "unpack_non_delta_entry()" to read the
entire contents of a blob object, no matter how big it is. This
implementation may consume all the memory and cause OOM.
By implementing a zstream version of input_stream interface, we can use
a small fixed buffer for "unpack_non_delta_entry()". However, unpack
non-delta objects from a stream instead of from an entrie buffer will
have 10% performance penalty.
$ hyperfine \
--setup \
'if ! test -d scalar.git; then git clone --bare
https://github.com/microsoft/scalar.git;
cp scalar.git/objects/pack/*.pack small.pack; fi' \
--prepare 'rm -rf dest.git && git init --bare dest.git' \
...
Summary
'./git -C dest.git -c core.bigFileThreshold=512m
unpack-objects <small.pack' in 'origin/master'
1.01 ± 0.04 times faster than './git -C dest.git
-c core.bigFileThreshold=512m unpack-objects
<small.pack' in 'HEAD~1'
1.01 ± 0.04 times faster than './git -C dest.git
-c core.bigFileThreshold=512m unpack-objects
<small.pack' in 'HEAD~0'
1.03 ± 0.10 times faster than './git -C dest.git
-c core.bigFileThreshold=16k unpack-objects
<small.pack' in 'origin/master'
1.02 ± 0.07 times faster than './git -C dest.git
-c core.bigFileThreshold=16k unpack-objects
<small.pack' in 'HEAD~0'
1.10 ± 0.04 times faster than './git -C dest.git
-c core.bigFileThreshold=16k unpack-objects
<small.pack' in 'HEAD~1'
Therefore, only unpack objects larger than the "core.bigFileThreshold"
in zstream. Until now, the config variable has been used in the
following cases, and our new case belongs to the packfile category.
* Archive:
+ archive.c: write_entry(): write large blob entries to archive in
stream.
* Loose objects:
+ object-file.c: index_fd(): when hashing large files in worktree,
read files in a stream, and create one packfile per large blob if
want to save files to git object store.
+ object-file.c: read_loose_object(): when checking loose objects
using "git-fsck", do not read full content of large loose objects.
* Packfile:
+ fast-import.c: parse_and_store_blob(): streaming large blob from
foreign source to packfile.
+ index-pack.c: check_collison(): read and check large blob in stream.
+ index-pack.c: unpack_entry_data(): do not return the entire
contents of the big blob from packfile, but uses a fixed buf to
perform some integrity checks on the object.
+ pack-check.c: verify_packfile(): used by "git-fsck" and will call
check_object_signature() to check large blob in pack with the
streaming interface.
+ pack-objects.c: get_object_details(): set "no_try_delta" for large
blobs when counting objects.
+ pack-objects.c: write_no_reuse_object(): streaming large blob to
pack.
+ unpack-objects.c: unpack_non_delta_entry(): unpack large blob in
stream from packfile.
* Others:
+ diff.c: diff_populate_filespec(): treat large blob file as binary.
+ streaming.c: istream_source(): as a helper of "open_istream()" to
select proper streaming interface to read large blob from packfile.
Helped-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
Helped-by: Derrick Stolee <stolee@xxxxxxxxx>
Helped-by: Jiang Xin <zhiyou.jx@xxxxxxxxxxxxxxx>
Signed-off-by: Han Xin <hanxin.hx@xxxxxxxxxxxxxxx>
---
builtin/unpack-objects.c | 71 ++++++++++++++++++++++++++++++++-
t/t5328-unpack-large-objects.sh | 23 +++++++++--
2 files changed, 90 insertions(+), 4 deletions(-)
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index c6d6c17072..e9ec2b349d 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -343,11 +343,80 @@ static void added_object(unsigned nr, enum object_type type,
}
}
+struct input_zstream_data {
+ git_zstream *zstream;
+ unsigned char buf[8192];
+ int status;
+};
+
+static const void *feed_input_zstream(struct input_stream *in_stream,
+ unsigned long *readlen)
+{
+ struct input_zstream_data *data = in_stream->data;
+ git_zstream *zstream = data->zstream;
+ void *in = fill(1);
+
+ if (in_stream->is_finished) {
+ *readlen = 0;
+ return NULL;
+ }
+
+ zstream->next_out = data->buf;
+ zstream->avail_out = sizeof(data->buf);
+ zstream->next_in = in;
+ zstream->avail_in = len;
+
+ data->status = git_inflate(zstream, 0);
+
+ in_stream->is_finished = data->status != Z_OK;
+ use(len - zstream->avail_in);
+ *readlen = sizeof(data->buf) - zstream->avail_out;
+
+ return data->buf;
+}
+
+static void write_stream_blob(unsigned nr, size_t size)
+{
+ git_zstream zstream = { 0 };
+ struct input_zstream_data data = { 0 };
+ struct input_stream in_stream = {
+ .read = feed_input_zstream,
+ .data = &data,
+ };
+
+ data.zstream = &zstream;
+ git_inflate_init(&zstream);
+
+ if (stream_loose_object(&in_stream, size, &obj_list[nr].oid))
+ die(_("failed to write object in stream"));
+
+ if (data.status != Z_STREAM_END)
+ die(_("inflate returned (%d)"), data.status);
+ git_inflate_end(&zstream);
+
+ if (strict) {
+ struct blob *blob =
+ lookup_blob(the_repository, &obj_list[nr].oid);
+ if (blob)
+ blob->object.flags |= FLAG_WRITTEN;
+ else
+ die(_("invalid blob object from stream"));
+ }
+ obj_list[nr].obj = NULL;
+}
+
static void unpack_non_delta_entry(enum object_type type, unsigned long size,
unsigned nr)
{
- void *buf = get_data(size);
+ void *buf;
+
+ /* Write large blob in stream without allocating full buffer. */
+ if (!dry_run && type == OBJ_BLOB && size > big_file_threshold) {
+ write_stream_blob(nr, size);
+ return;
+ }
+ buf = get_data(size);
if (buf)
write_object(nr, type, buf, size);
}
diff --git a/t/t5328-unpack-large-objects.sh b/t/t5328-unpack-large-objects.sh
index 45a3316e06..f4129979f9 100755
--- a/t/t5328-unpack-large-objects.sh
+++ b/t/t5328-unpack-large-objects.sh
@@ -9,7 +9,11 @@ test_description='git unpack-objects with large objects'
prepare_dest () {
test_when_finished "rm -rf dest.git" &&
- git init --bare dest.git
+ git init --bare dest.git &&
+ if test -n "$1"
+ then
+ git -C dest.git config core.bigFileThreshold $1
+ fi
}
test_no_loose () {
@@ -33,16 +37,29 @@ test_expect_success 'set memory limitation to 1MB' '
'
test_expect_success 'unpack-objects failed under memory limitation' '
- prepare_dest &&
+ prepare_dest 2m &&
test_must_fail git -C dest.git unpack-objects <test-$PACK.pack 2>err &&
grep "fatal: attempting to allocate" err
'
test_expect_success 'unpack-objects works with memory limitation in dry-run mode' '
- prepare_dest &&
+ prepare_dest 2m &&
git -C dest.git unpack-objects -n <test-$PACK.pack &&
test_no_loose &&
test_dir_is_empty dest.git/objects/pack
'
+test_expect_success 'unpack big object in stream' '
+ prepare_dest 1m &&
+ git -C dest.git unpack-objects <test-$PACK.pack &&
+ test_dir_is_empty dest.git/objects/pack
+'
+
+test_expect_success 'do not unpack existing large objects' '
+ prepare_dest 1m &&
+ git -C dest.git index-pack --stdin <test-$PACK.pack &&
+ git -C dest.git unpack-objects <test-$PACK.pack &&
+ test_no_loose
+'
+
test_done
--
2.34.1.52.gc288e771b4.agit.6.5.6
