Revision b16a8277644e4b1d21c08d97de757105039dc7ae authored by Derrick Stolee on 16 September 2020, 18:07:52 UTC, committed by Junio C Hamano on 17 September 2020, 16:31:25 UTC
Commit e3696980 (diff: halt tree-diff early after max_changes, 2020-03-30) intended to create a mechanism to short-circuit a diff calculation after a certain number of paths were modified. By incrementing a "num_changes" counter throughout the recursive ll_diff_tree_paths(), this was supposed to match the number of changes that would be written into the changed-path Bloom filters. Unfortunately, this was not implemented correctly and instead misses simple cases like file modifications. This then does not stop very large changed-path filters from being written (unless they add or remove many files). To start, change the implementation in ll_diff_tree_paths() to instead use the global diff_queue_diff struct's 'nr' member as the count. This is a way to simplify the logic instead of making more mistakes in the complicated diff code. This has a drawback: the diff_queue_diff struct only lists the paths corresponding to blob changes, not their leading directories. Thus, get_or_compute_bloom_filter() needs an additional check to see if the hashmap with the leading directories becomes too large. One reason why this was not caught by test cases was that the test in t4216-log-bloom.sh that was supposed to check this "too many changes" condition only checked this on the initial commit of a repository. The old logic counted these values correctly. Update this test in a few ways: 1. Use GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS to reduce the limit, allowing smaller commits to engage with this logic. 2. Create several interesting cases of edits, adds, removes, and mode changes (in the second commit). By testing both sides of the inequality with the *_MAX_CHANGED_PATHS variable, we can see that the count is exactly correct, so none of these changes are missed or over-counted. 3. Use the trace2 data value filter_found_large to verify that these commits are on the correct side of the limit. Another way to verify the behavior is correct is through performance tests. By testing on my local copies of the Git repository and the Linux kernel repository, I could measure the effect of these short-circuits when computing a fresh commit-graph file with changed-path Bloom filters using the command GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS=N time \ git commit-graph write --reachable --changed-paths and reporting the wall time and resulting commit-graph size. For Git, the results are | | N=1 | N=10 | N=512 | |--------|----------------|----------------|----------------| | HEAD~1 | 10.90s 9.18MB | 11.11s 9.34MB | 11.31s 9.35MB | | HEAD | 9.21s 8.62MB | 11.11s 9.29MB | 11.29s 9.34MB | For Linux, the results are | | N=1 | N=20 | N=512 | |--------|----------------|---------------|---------------| | HEAD~1 | 61.28s 64.3MB | 76.9s 72.6MB | 77.6s 72.6MB | | HEAD | 49.44s 56.3MB | 68.7s 65.9MB | 69.2s 65.9MB | Naturally, the improvement becomes much less as the limit grows, as fewer commits satisfy the short-circuit. Reported-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
1 parent 9a7a9ed
zlib.c
/*
* zlib wrappers to make sure we don't silently miss errors
* at init time.
*/
#include "cache.h"
static const char *zerr_to_string(int status)
{
switch (status) {
case Z_MEM_ERROR:
return "out of memory";
case Z_VERSION_ERROR:
return "wrong version";
case Z_NEED_DICT:
return "needs dictionary";
case Z_DATA_ERROR:
return "data stream error";
case Z_STREAM_ERROR:
return "stream consistency error";
default:
return "unknown error";
}
}
/*
* avail_in and avail_out in zlib are counted in uInt, which typically
* limits the size of the buffer we can use to 4GB when interacting
* with zlib in a single call to inflate/deflate.
*/
/* #define ZLIB_BUF_MAX ((uInt)-1) */
#define ZLIB_BUF_MAX ((uInt) 1024 * 1024 * 1024) /* 1GB */
static inline uInt zlib_buf_cap(unsigned long len)
{
return (ZLIB_BUF_MAX < len) ? ZLIB_BUF_MAX : len;
}
static void zlib_pre_call(git_zstream *s)
{
s->z.next_in = s->next_in;
s->z.next_out = s->next_out;
s->z.total_in = s->total_in;
s->z.total_out = s->total_out;
s->z.avail_in = zlib_buf_cap(s->avail_in);
s->z.avail_out = zlib_buf_cap(s->avail_out);
}
static void zlib_post_call(git_zstream *s)
{
unsigned long bytes_consumed;
unsigned long bytes_produced;
bytes_consumed = s->z.next_in - s->next_in;
bytes_produced = s->z.next_out - s->next_out;
if (s->z.total_out != s->total_out + bytes_produced)
BUG("total_out mismatch");
if (s->z.total_in != s->total_in + bytes_consumed)
BUG("total_in mismatch");
s->total_out = s->z.total_out;
s->total_in = s->z.total_in;
s->next_in = s->z.next_in;
s->next_out = s->z.next_out;
s->avail_in -= bytes_consumed;
s->avail_out -= bytes_produced;
}
void git_inflate_init(git_zstream *strm)
{
int status;
zlib_pre_call(strm);
status = inflateInit(&strm->z);
zlib_post_call(strm);
if (status == Z_OK)
return;
die("inflateInit: %s (%s)", zerr_to_string(status),
strm->z.msg ? strm->z.msg : "no message");
}
void git_inflate_init_gzip_only(git_zstream *strm)
{
/*
* Use default 15 bits, +16 is to accept only gzip and to
* yield Z_DATA_ERROR when fed zlib format.
*/
const int windowBits = 15 + 16;
int status;
zlib_pre_call(strm);
status = inflateInit2(&strm->z, windowBits);
zlib_post_call(strm);
if (status == Z_OK)
return;
die("inflateInit2: %s (%s)", zerr_to_string(status),
strm->z.msg ? strm->z.msg : "no message");
}
void git_inflate_end(git_zstream *strm)
{
int status;
zlib_pre_call(strm);
status = inflateEnd(&strm->z);
zlib_post_call(strm);
if (status == Z_OK)
return;
error("inflateEnd: %s (%s)", zerr_to_string(status),
strm->z.msg ? strm->z.msg : "no message");
}
int git_inflate(git_zstream *strm, int flush)
{
int status;
for (;;) {
zlib_pre_call(strm);
/* Never say Z_FINISH unless we are feeding everything */
status = inflate(&strm->z,
(strm->z.avail_in != strm->avail_in)
? 0 : flush);
if (status == Z_MEM_ERROR)
die("inflate: out of memory");
zlib_post_call(strm);
/*
* Let zlib work another round, while we can still
* make progress.
*/
if ((strm->avail_out && !strm->z.avail_out) &&
(status == Z_OK || status == Z_BUF_ERROR))
continue;
break;
}
switch (status) {
/* Z_BUF_ERROR: normal, needs more space in the output buffer */
case Z_BUF_ERROR:
case Z_OK:
case Z_STREAM_END:
return status;
default:
break;
}
error("inflate: %s (%s)", zerr_to_string(status),
strm->z.msg ? strm->z.msg : "no message");
return status;
}
#if defined(NO_DEFLATE_BOUND) || ZLIB_VERNUM < 0x1200
#define deflateBound(c,s) ((s) + (((s) + 7) >> 3) + (((s) + 63) >> 6) + 11)
#endif
unsigned long git_deflate_bound(git_zstream *strm, unsigned long size)
{
return deflateBound(&strm->z, size);
}
void git_deflate_init(git_zstream *strm, int level)
{
int status;
memset(strm, 0, sizeof(*strm));
zlib_pre_call(strm);
status = deflateInit(&strm->z, level);
zlib_post_call(strm);
if (status == Z_OK)
return;
die("deflateInit: %s (%s)", zerr_to_string(status),
strm->z.msg ? strm->z.msg : "no message");
}
static void do_git_deflate_init(git_zstream *strm, int level, int windowBits)
{
int status;
memset(strm, 0, sizeof(*strm));
zlib_pre_call(strm);
status = deflateInit2(&strm->z, level,
Z_DEFLATED, windowBits,
8, Z_DEFAULT_STRATEGY);
zlib_post_call(strm);
if (status == Z_OK)
return;
die("deflateInit2: %s (%s)", zerr_to_string(status),
strm->z.msg ? strm->z.msg : "no message");
}
void git_deflate_init_gzip(git_zstream *strm, int level)
{
/*
* Use default 15 bits, +16 is to generate gzip header/trailer
* instead of the zlib wrapper.
*/
do_git_deflate_init(strm, level, 15 + 16);
}
void git_deflate_init_raw(git_zstream *strm, int level)
{
/*
* Use default 15 bits, negate the value to get raw compressed
* data without zlib header and trailer.
*/
do_git_deflate_init(strm, level, -15);
}
int git_deflate_abort(git_zstream *strm)
{
int status;
zlib_pre_call(strm);
status = deflateEnd(&strm->z);
zlib_post_call(strm);
return status;
}
void git_deflate_end(git_zstream *strm)
{
int status = git_deflate_abort(strm);
if (status == Z_OK)
return;
error("deflateEnd: %s (%s)", zerr_to_string(status),
strm->z.msg ? strm->z.msg : "no message");
}
int git_deflate_end_gently(git_zstream *strm)
{
int status;
zlib_pre_call(strm);
status = deflateEnd(&strm->z);
zlib_post_call(strm);
return status;
}
int git_deflate(git_zstream *strm, int flush)
{
int status;
for (;;) {
zlib_pre_call(strm);
/* Never say Z_FINISH unless we are feeding everything */
status = deflate(&strm->z,
(strm->z.avail_in != strm->avail_in)
? 0 : flush);
if (status == Z_MEM_ERROR)
die("deflate: out of memory");
zlib_post_call(strm);
/*
* Let zlib work another round, while we can still
* make progress.
*/
if ((strm->avail_out && !strm->z.avail_out) &&
(status == Z_OK || status == Z_BUF_ERROR))
continue;
break;
}
switch (status) {
/* Z_BUF_ERROR: normal, needs more space in the output buffer */
case Z_BUF_ERROR:
case Z_OK:
case Z_STREAM_END:
return status;
default:
break;
}
error("deflate: %s (%s)", zerr_to_string(status),
strm->z.msg ? strm->z.msg : "no message");
return status;
}
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