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| author | Han Xin <hanxin.hx@alibaba-inc.com> | 2022-06-11 10:44:16 +0800 |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2022-06-13 10:22:35 -0700 |
| commit | a1bf5ca29f7ebb41e24318147518fc7c738303e5 (patch) | |
| tree | 12bd174f216456e38cb12cd4624b59b3bd0335b9 | |
| parent | ab336e8f1c8009c8b1aab8deb592148e69217085 (diff) | |
| download | git-a1bf5ca29f7ebb41e24318147518fc7c738303e5.tar.gz | |
unpack-objects: low memory footprint for get_data() in dry_run mode
As the name implies, "get_data(size)" will allocate and return a given
amount of memory. Allocating memory for a large blob object may cause the
system to run out of memory. Before preparing to replace calling of
"get_data()" to unpack large blob objects in latter commits, refactor
"get_data()" to reduce memory footprint for dry_run mode.
Because in dry_run mode, "get_data()" is only used to check the
integrity of data, and the returned buffer is not used at all, we can
allocate a smaller buffer and use it as zstream output. Make the function
return NULL in the dry-run mode, as no callers use the returned buffer.
The "find [...]objects/?? -type f | wc -l" test idiom being used here
is adapted from the same "find" use added to another test in
d9545c7f465 (fast-import: implement unpack limit, 2016-04-25).
Suggested-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
Signed-off-by: Han Xin <chiyutianyi@gmail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
| -rw-r--r-- | builtin/unpack-objects.c | 37 | ||||
| -rwxr-xr-x | t/t5351-unpack-large-objects.sh | 41 |
2 files changed, 67 insertions, 11 deletions
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c index 56d05e2725..32e8b47059 100644 --- a/builtin/unpack-objects.c +++ b/builtin/unpack-objects.c @@ -97,15 +97,27 @@ static void use(int bytes) display_throughput(progress, consumed_bytes); } +/* + * Decompress zstream from the standard input into a newly + * allocated buffer of specified size and return the buffer. + * The caller is responsible to free the returned buffer. + * + * But for dry_run mode, "get_data()" is only used to check the + * integrity of data, and the returned buffer is not used at all. + * Therefore, in dry_run mode, "get_data()" will release the small + * allocated buffer which is reused to hold temporary zstream output + * and return NULL instead of returning garbage data. + */ static void *get_data(unsigned long size) { git_zstream stream; - void *buf = xmallocz(size); + unsigned long bufsize = dry_run && size > 8192 ? 8192 : size; + void *buf = xmallocz(bufsize); memset(&stream, 0, sizeof(stream)); stream.next_out = buf; - stream.avail_out = size; + stream.avail_out = bufsize; stream.next_in = fill(1); stream.avail_in = len; git_inflate_init(&stream); @@ -125,8 +137,17 @@ static void *get_data(unsigned long size) } stream.next_in = fill(1); stream.avail_in = len; + if (dry_run) { + /* reuse the buffer in dry_run mode */ + stream.next_out = buf; + stream.avail_out = bufsize > size - stream.total_out ? + size - stream.total_out : + bufsize; + } } git_inflate_end(&stream); + if (dry_run) + FREE_AND_NULL(buf); return buf; } @@ -326,10 +347,8 @@ static void unpack_non_delta_entry(enum object_type type, unsigned long size, { void *buf = get_data(size); - if (!dry_run && buf) + if (buf) write_object(nr, type, buf, size); - else - free(buf); } static int resolve_against_held(unsigned nr, const struct object_id *base, @@ -359,10 +378,8 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size, oidread(&base_oid, fill(the_hash_algo->rawsz)); use(the_hash_algo->rawsz); delta_data = get_data(delta_size); - if (dry_run || !delta_data) { - free(delta_data); + if (!delta_data) return; - } if (has_object_file(&base_oid)) ; /* Ok we have this one */ else if (resolve_against_held(nr, &base_oid, @@ -398,10 +415,8 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size, die("offset value out of bound for delta base object"); delta_data = get_data(delta_size); - if (dry_run || !delta_data) { - free(delta_data); + if (!delta_data) return; - } lo = 0; hi = nr; while (lo < hi) { diff --git a/t/t5351-unpack-large-objects.sh b/t/t5351-unpack-large-objects.sh new file mode 100755 index 0000000000..8d84313221 --- /dev/null +++ b/t/t5351-unpack-large-objects.sh @@ -0,0 +1,41 @@ +#!/bin/sh +# +# Copyright (c) 2022 Han Xin +# + +test_description='git unpack-objects with large objects' + +. ./test-lib.sh + +prepare_dest () { + test_when_finished "rm -rf dest.git" && + git init --bare dest.git +} + +test_expect_success "create large objects (1.5 MB) and PACK" ' + test-tool genrandom foo 1500000 >big-blob && + test_commit --append foo big-blob && + test-tool genrandom bar 1500000 >big-blob && + test_commit --append bar big-blob && + PACK=$(echo HEAD | git pack-objects --revs pack) +' + +test_expect_success 'set memory limitation to 1MB' ' + GIT_ALLOC_LIMIT=1m && + export GIT_ALLOC_LIMIT +' + +test_expect_success 'unpack-objects failed under memory limitation' ' + prepare_dest && + test_must_fail git -C dest.git unpack-objects <pack-$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 && + git -C dest.git unpack-objects -n <pack-$PACK.pack && + test_stdout_line_count = 0 find dest.git/objects -type f && + test_dir_is_empty dest.git/objects/pack +' + +test_done |