git/line-log.c, branch v2.35.3

use CALLOC_ARRAY

2021-03-14T00:00:09Z

Add and apply a semantic patch for converting code that open-codes CALLOC_ARRAY to use it instead. It shortens the code and infers the element size automatically. Signed-off-by: René Scharfe Signed-off-by: Junio C Hamano

line-log: handle deref_tag() returning NULL

2020-10-12T19:25:14Z

Signed-off-by: René Scharfe Signed-off-by: Junio C Hamano

Merge branch 'tb/bloom-improvements'

2020-09-29T21:01:20Z

"git commit-graph write" learned to limit the number of bloom filters that are computed from scratch with the --max-new-filters option. * tb/bloom-improvements: commit-graph: introduce 'commitGraph.maxNewFilters' builtin/commit-graph.c: introduce '--max-new-filters=' commit-graph: rename 'split_commit_graph_opts' bloom: encode out-of-bounds filters as non-empty bloom/diff: properly short-circuit on max_changes bloom: use provided 'struct bloom_filter_settings' bloom: split 'get_bloom_filter()' in two commit-graph.c: store maximum changed paths commit-graph: respect 'commitGraph.readChangedPaths' t/helper/test-read-graph.c: prepare repo settings commit-graph: pass a 'struct repository *' in more places t4216: use an '&&'-chain commit-graph: introduce 'get_bloom_filter_settings()'

bloom: split 'get_bloom_filter()' in two

2020-09-17T16:31:25Z

'get_bloom_filter' takes a flag to control whether it will compute a Bloom filter if the requested one is missing. In the next patch, we'll add yet another parameter to this method, which would force all but one caller to specify an extra 'NULL' parameter at the end. Instead of doing this, split 'get_bloom_filter' into two functions: 'get_bloom_filter' and 'get_or_compute_bloom_filter'. The former only looks up a Bloom filter (and does not compute one if it's missing, thus dropping the 'compute_if_not_present' flag). The latter does compute missing Bloom filters, with an additional parameter to store whether or not it needed to do so. This simplifies many call-sites, since the majority of existing callers to 'get_bloom_filter' do not want missing Bloom filters to be computed (so they can drop the parameter entirely and use the simpler version of the function). While we're at it, instrument the new 'get_or_compute_bloom_filter()' with counters in the 'write_commit_graph_context' struct which store the number of filters that we did and didn't compute, as well as filters that were truncated. It would be nice to drop the 'compute_if_not_present' flag entirely, since all remaining callers of 'get_or_compute_bloom_filter' pass it as '1', but this will change in a future patch and hence cannot be removed. Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano

strvec: convert more callers away from argv_array name

2020-07-28T22:02:18Z

We eventually want to drop the argv_array name and just use strvec consistently. There's no particular reason we have to do it all at once, or care about interactions between converted and unconverted bits. Because of our preprocessor compat layer, the names are interchangeable to the compiler (so even a definition and declaration using different names is OK). This patch converts remaining files from the first half of the alphabet, to keep the diff to a manageable size. The conversion was done purely mechanically with: git ls-files '*.c' '*.h' | xargs perl -i -pe ' s/ARGV_ARRAY/STRVEC/g; s/argv_array/strvec/g; ' and then selectively staging files with "git add '[abcdefghjkl]*'". We'll deal with any indentation/style fallouts separately. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

strvec: rename files from argv-array to strvec

2020-07-28T22:02:17Z

This requires updating #include lines across the code-base, but that's all fairly mechanical, and was done with: git ls-files '*.c' '*.h' | xargs perl -i -pe 's/argv-array.h/strvec.h/' Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

Merge branch 'ds/line-log-on-bloom'

2020-06-09T01:06:26Z

"git log -L..." now takes advantage of the "which paths are touched by this commit?" info stored in the commit-graph system. * ds/line-log-on-bloom: line-log: integrate with changed-path Bloom filters line-log: try to use generation number-based topo-ordering line-log: more responsive, incremental 'git log -L' t4211-line-log: add tests for parent oids line-log: remove unused fields from 'struct line_log_data'

line-log: integrate with changed-path Bloom filters

2020-05-11T16:33:56Z

The previous changes to the line-log machinery focused on making the first result appear faster. This was achieved by no longer walking the entire commit history before returning the early results. There is still another way to improve the performance: walk most commits much faster. Let's use the changed-path Bloom filters to reduce time spent computing diffs. Since the line-log computation requires opening blobs and checking the content-diff, there is still a lot of necessary computation that cannot be replaced with changed-path Bloom filters. The part that we can reduce is most effective when checking the history of a file that is deep in several directories and those directories are modified frequently. In this case, the computation to check if a commit is TREESAME to its first parent takes a large fraction of the time. That is ripe for improvement with changed-path Bloom filters. We must ensure that prepare_to_use_bloom_filters() is called in revision.c so that the bloom_filter_settings are loaded into the struct rev_info from the commit-graph. Of course, some cases are still forbidden, but in the line-log case the pathspec is provided in a different way than normal. Since multiple paths and segments could be requested, we compute the struct bloom_key data dynamically during the commit walk. This could likely be improved, but adds code complexity that is not valuable at this time. There are two cases to care about: merge commits and "ordinary" commits. Merge commits have multiple parents, but if we are TREESAME to our first parent in every range, then pass the blame for all ranges to the first parent. Ordinary commits have the same condition, but each is done slightly differently in the process_ranges_[merge|ordinary]_commit() methods. By checking if the changed-path Bloom filter can guarantee TREESAME, we can avoid that tree-diff cost. If the filter says "probably changed", then we need to run the tree-diff and then the blob-diff if there was a real edit. The Linux kernel repository is a good testing ground for the performance improvements claimed here. There are two different cases to test. The first is the "entire history" case, where we output the entire history to /dev/null to see how long it would take to compute the full line-log history. The second is the "first result" case, where we find how long it takes to show the first value, which is an indicator of how quickly a user would see responses when waiting at a terminal. To test, I selected the paths that were changed most frequently in the top 10,000 commits using this command (stolen from StackOverflow [1]): git log --pretty=format: --name-only -n 10000 | sort | \ uniq -c | sort -rg | head -10 which results in 121 MAINTAINERS 63 fs/namei.c 60 arch/x86/kvm/cpuid.c 59 fs/io_uring.c 58 arch/x86/kvm/vmx/vmx.c 51 arch/x86/kvm/x86.c 45 arch/x86/kvm/svm.c 42 fs/btrfs/disk-io.c 42 Documentation/scsi/index.rst (along with a bogus first result). It appears that the path arch/x86/kvm/svm.c was renamed, so we ignore that entry. This leaves the following results for the real command time: | | Entire History | First Result | | Path | Before | After | Before | After | |------------------------------|--------|--------|--------|--------| | MAINTAINERS | 4.26 s | 3.87 s | 0.41 s | 0.39 s | | fs/namei.c | 1.99 s | 0.99 s | 0.42 s | 0.21 s | | arch/x86/kvm/cpuid.c | 5.28 s | 1.12 s | 0.16 s | 0.09 s | | fs/io_uring.c | 4.34 s | 0.99 s | 0.94 s | 0.27 s | | arch/x86/kvm/vmx/vmx.c | 5.01 s | 1.34 s | 0.21 s | 0.12 s | | arch/x86/kvm/x86.c | 2.24 s | 1.18 s | 0.21 s | 0.14 s | | fs/btrfs/disk-io.c | 1.82 s | 1.01 s | 0.06 s | 0.05 s | | Documentation/scsi/index.rst | 3.30 s | 0.89 s | 1.46 s | 0.03 s | It is worth noting that the least speedup comes for the MAINTAINERS file which is * edited frequently, * low in the directory heirarchy, and * quite a large file. All of those points lead to spending more time doing the blob diff and less time doing the tree diff. Still, we see some improvement in that case and significant improvement in other cases. A 2-4x speedup is likely the more typical case as opposed to the small 5% change for that file. Signed-off-by: Derrick Stolee Signed-off-by: Junio C Hamano

line-log: more responsive, incremental 'git log -L'

2020-05-11T16:33:56Z

The current line-level log implementation performs a preprocessing step in prepare_revision_walk(), during which the line_log_filter() function filters and rewrites history to keep only commits modifying the given line range. This preprocessing affects both responsiveness and correctness: - Git doesn't produce any output during this preprocessing step. Checking whether a commit modified the given line range is somewhat expensive, so depending on the size of the given revision range this preprocessing can result in a significant delay before the first commit is shown. - Limiting the number of displayed commits (e.g. 'git log -3 -L...') doesn't limit the amount of work during preprocessing, because that limit is applied during history traversal. Alas, by that point this expensive preprocessing step has already churned through the whole revision range to find all commits modifying the revision range, even though only a few of them need to be shown. - It rewrites parents, with no way to turn it off. Without the user explicitly requesting parent rewriting any parent object ID shown should be that of the immediate parent, just like in case of a pathspec-limited history traversal without parent rewriting. However, after that preprocessing step rewrote history, the subsequent "regular" history traversal (i.e. get_revision() in a loop) only sees commits modifying the given line range. Consequently, it can only show the object ID of the last ancestor that modified the given line range (which might happen to be the immediate parent, but many-many times it isn't). This patch addresses both the correctness and, at least for the common case, the responsiveness issues by integrating line-level log filtering into the regular revision walking machinery: - Make process_ranges_arbitrary_commit(), the static function in 'line-log.c' deciding whether a commit modifies the given line range, public by removing the static keyword and adding the 'line_log_' prefix, so it can be called from other parts of the revision walking machinery. - If the user didn't explicitly ask for parent rewriting (which, I believe, is the most common case): - Call this now-public function during regular history traversal, namely from get_commit_action() to ignore any commits not modifying the given line range. Note that while this check is relatively expensive, it must be performed before other, much cheaper conditions, because the tracked line range must be adjusted even when the commit will end up being ignored by other conditions. - Skip the line_log_filter() call, i.e. the expensive preprocessing step, in prepare_revision_walk(), because, thanks to the above points, the revision walking machinery is now able to filter out commits not modifying the given line range while traversing history. This way the regular history traversal sees the unmodified history, and is therefore able to print the object ids of the immediate parents of the listed commits. The eliminated preprocessing step can greatly reduce the delay before the first commit is shown, see the numbers below. - However, if the user did explicitly ask for parent rewriting via '--parents' or a similar option, then stick with the current implementation for now, i.e. perform that expensive filtering and history rewriting in the preprocessing step just like we did before, leaving the initial delay as long as it was. I tried to integrate line-level log filtering with parent rewriting into the regular history traversal, but, unfortunately, several subtleties resisted... :) Maybe someday we'll figure out how to do that, but until then at least the simple and common (i.e. without parent rewriting) 'git log -L:func:file' commands can benefit from the reduced delay. This change makes the failing 'parent oids without parent rewriting' test in 't4211-line-log.sh' succeed. The reduced delay is most noticable when there's a commit modifying the line range near the tip of a large-ish revision range: # no parent rewriting requested, no commit-graph present $ time git --no-pager log -L:read_alternate_refs:sha1-file.c -1 v2.23.0 Before: real 0m9.570s user 0m9.494s sys 0m0.076s After: real 0m0.718s user 0m0.674s sys 0m0.044s A significant part of the remaining delay is spent reading and parsing commit objects in limit_list(). With the help of the commit-graph we can eliminate most of that reading and parsing overhead, so here are the timing results of the same command as above, but this time using the commit-graph: Before: real 0m8.874s user 0m8.816s sys 0m0.057s After: real 0m0.107s user 0m0.091s sys 0m0.013s The next patch will further reduce the remaining delay. To be clear: this patch doesn't actually optimize the line-level log, but merely moves most of the work from the preprocessing step to the history traversal, so the commits modifying the line range can be shown as soon as they are processed, and the traversal can be terminated as soon as the given number of commits are shown. Consequently, listing the full history of a line range, potentially all the way to the root commit, will take the same time as before (but at least the user might start reading the output earlier). Furthermore, if the most recent commit modifying the line range is far away from the starting revision, then that initial delay will still be significant. Additional testing by Derrick Stolee: In the Linux kernel repository, the MAINTAINERS file was changed ~3,500 times across the ~915,000 commits. In addition to that edit frequency, the file itself is quite large (~18,700 lines). This means that a significant portion of the computation is taken up by computing the patch-diff of the file. This patch improves the real time it takes to output the first result quite a bit: Command: git log -L 100,200:MAINTAINERS -n 1 >/dev/null Before: 3.88 s After: 0.71 s If we drop the "-n 1" in the command, then there is no change in end-to-end process time. This is because the command still needs to walk the entire commit history, which negates the point of this patch. This is expected. As a note for future reference, the ~4.3 seconds in the old code spends ~2.6 seconds computing the patch-diffs, and the rest of the time is spent walking commits and computing diffs for which paths changed at each commit. The changed-path Bloom filters could improve the end-to-end computation time (i.e. no "-n 1" in the command). Signed-off-by: SZEDER Gábor Signed-off-by: Derrick Stolee Signed-off-by: Junio C Hamano

diff: make diff_populate_filespec_options struct

2020-04-07T23:09:29Z

The behavior of diff_populate_filespec() currently can be customized through a bitflag, but a subsequent patch requires it to support a non-boolean option. Replace the bitflag with an options struct. Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano