git/commit-reach.c, branch v2.28.1

Merge branch 'cb/is-descendant-of'

2020-07-07T05:09:16Z

Code clean-up. * cb/is-descendant-of: commit-reach: avoid is_descendant_of() shim

Merge branch 'ak/commit-graph-to-slab'

2020-07-07T05:09:14Z

A few fields in "struct commit" that do not have to always be present have been moved to commit slabs. * ak/commit-graph-to-slab: commit-graph: minimize commit_graph_data_slab access commit: move members graph_pos, generation to a slab commit-graph: introduce commit_graph_data_slab object: drop parsed_object_pool->commit_count

Merge branch 'rs/commit-reach-leakfix'

2020-06-29T21:17:27Z

Leakfix. * rs/commit-reach-leakfix: commit-reach: plug minor memory leak after using is_descendant_of()

commit-reach: avoid is_descendant_of() shim

2020-06-23T23:36:53Z

d91d6fbf26 (commit-reach: create repo_is_descendant_of(), 2020-06-17) adds a repository aware version of is_descendant_of() and a backward compatibility shim that is barely used. Update all callers to directly use the new repo_is_descendant_of() function instead; making the codebase simpler and pushing more the_repository references higher up the stack. Helped-by: Derrick Stolee Signed-off-by: Carlo Marcelo Arenas Belón Reviewed-by: Derrick Stolee Signed-off-by: Junio C Hamano

commit-reach: plug minor memory leak after using is_descendant_of()

2020-06-19T18:06:01Z

ref_newer() builds a commit_list to pass a single potential ancestor to is_descendant_of(). The latter leaves the list intact. Release the allocated memory after the call. Signed-off-by: René Scharfe Acked-by: Derrick Stolee Signed-off-by: Junio C Hamano

commit-graph: minimize commit_graph_data_slab access

2020-06-17T21:37:52Z

In an earlier patch, multiple struct acccesses to `graph_pos` and `generation` were auto-converted to multiple method calls. Since the values are fixed and commit-slab access costly, we would be better off with storing the values as a local variable and reusing it. Signed-off-by: Abhishek Kumar Signed-off-by: Junio C Hamano

commit: move members graph_pos, generation to a slab

2020-06-17T21:37:30Z

We remove members `graph_pos` and `generation` from the struct commit. The default assignments in init_commit_node() are no longer valid, which is fine as the slab helpers return appropriate default values and the assignments are removed. We will replace existing use of commit->generation and commit->graph_pos by commit_graph_data_slab helpers using `contrib/coccinelle/commit.cocci'. Signed-off-by: Abhishek Kumar Signed-off-by: Junio C Hamano

commit-reach: use fast logic in repo_in_merge_base

2020-06-17T20:49:38Z

The repo_is_descendant_of() method is aware of the existence of the commit-graph file. It checks for generation_numbers_enabled() before deciding on using can_all_from_reach() or repo_in_merge_bases() depending on the situation. The reason here is that can_all_from_reach() uses a depth-first search that is limited by the minimum generation number of the target commits, and that algorithm can be very slow when generation numbers are not present. The alternative uses paint_down_to_common() which will walk the entire merge-base boundary, which is typically slower. This method is used by commands like "git tag --contains" and "git branch --contains" for very fast results when a commit-graph file exists. Unfortunately, it is _not_ used in commands like "git merge-base --is-ancestor" which is doing an even simpler request. This issue was raised recently [1] with respect to a change to how generation numbers are stored, but was also reported much earlier [2] before commit-reach.c existed to simplify these reachability queries. [1] https://lore.kernel.org/git/20200607195347.GA8232@szeder.dev/ [2] https://lore.kernel.org/git/87608bawoa.fsf@evledraar.gmail.com/ The root cause is that builtin/merge-base.c has a method handle_is_ancestor() that calls in_merge_bases(), an older version of repo_in_merge_bases(). It would be better if we have every caller to in_merge_bases() use the logic in can_all_from_reach() when possible. This is where things get a little tricky: repo_is_descendant_of() calls repo_in_merge_bases() in the non-generation numbers enabled case! If we simply update repo_in_merge_bases() to call repo_is_descendant_of() instead of repo_in_merge_bases_many(), then we will get a recursive call loop. Thankfully, this is caught by the test suite in the default mode (i.e. GIT_TEST_COMMIT_GRAPH=0). The trick, then, is to make the non-generation number case for repo_is_descendant_of() call repo_in_merge_bases_many() directly, skipping the non-_many version. This allows us to take advantage of this faster code path, when possible. The easiest way to measure the performance impact is to test the following command on the Linux kernel repository: git merge-base --is-ancestor | A | B | Time Before | Time After | |------|------|-------------|------------| | v3.0 | v5.7 | 0.459s | 0.028s | | v4.0 | v5.7 | 0.267s | 0.021s | | v5.0 | v5.7 | 0.074s | 0.013s | Note that each of these samples return success. The old code performed the same operation when and are swapped. However, can_all_from_reach() will return immediately if the generation numbers show that has larger generation number than . Thus, the time for the swapped case is universally 0.004s in each case. Reported-by: Ævar Arnfjörð Bjarmason Reported-by: SZEDER Gábor Signed-off-by: Derrick Stolee Signed-off-by: Junio C Hamano

commit-reach: create repo_is_descendant_of()

2020-06-17T20:49:36Z
The next change will make repo_in_merge_bases() depend on the logic in is_descendant_of(), but we need to make the method independent of the_repository first. Signed-off-by: Derrick Stolee Signed-off-by: Junio C Hamano

commit-graph: fix writing first commit-graph during fetch

2019-10-25T02:19:16Z
The previous commit includes a failing test for an issue around fetch.writeCommitGraph and fetching in a repo with a submodule. Here, we fix that bug and set the test to "test_expect_success". The problem arises with this set of commands when the remote repo at has a submodule. Note that --recurse-submodules is not needed to demonstrate the bug. $ git clone test $ cd test $ git -c fetch.writeCommitGraph=true fetch origin Computing commit graph generation numbers: 100% (12/12), done. BUG: commit-graph.c:886: missing parent for commit Aborted (core dumped) As an initial fix, I converted the code in builtin/fetch.c that calls write_commit_graph_reachable() to instead launch a "git commit-graph write --reachable --split" process. That code worked, but is not how we want the feature to work long-term. That test did demonstrate that the issue must be something to do with internal state of the 'git fetch' process. The write_commit_graph() method in commit-graph.c ensures the commits we plan to write are "closed under reachability" using close_reachable(). This method walks from the input commits, and uses the UNINTERESTING flag to mark which commits have already been visited. This allows the walk to take O(N) time, where N is the number of commits, instead of O(P) time, where P is the number of paths. (The number of paths can be exponential in the number of commits.) However, the UNINTERESTING flag is used in lots of places in the codebase. This flag usually means some barrier to stop a commit walk, such as in revision-walking to compare histories. It is not often cleared after the walk completes because the starting points of those walks do not have the UNINTERESTING flag, and clear_commit_marks() would stop immediately. This is happening during a 'git fetch' call with a remote. The fetch negotiation is comparing the remote refs with the local refs and marking some commits as UNINTERESTING. I tested running clear_commit_marks_many() to clear the UNINTERESTING flag inside close_reachable(), but the tips did not have the flag, so that did nothing. It turns out that the calculate_changed_submodule_paths() method is at fault. Thanks, Peff, for pointing out this detail! More specifically, for each submodule, the collect_changed_submodules() runs a revision walk to essentially do file-history on the list of submodules. That revision walk marks commits UNININTERESTING if they are simplified away by not changing the submodule. Instead, I finally arrived on the conclusion that I should use a flag that is not used in any other part of the code. In commit-reach.c, a number of flags were defined for commit walk algorithms. The REACHABLE flag seemed like it made the most sense, and it seems it was not actually used in the file. The REACHABLE flag was used in early versions of commit-reach.c, but was removed by 4fbcca4 (commit-reach: make can_all_from_reach... linear, 2018-07-20). Add the REACHABLE flag to commit-graph.c and use it instead of UNINTERESTING in close_reachable(). This fixes the bug in manual testing. Reported-by: Johannes Schindelin Helped-by: Jeff King Helped-by: Szeder Gábor Signed-off-by: Derrick Stolee Signed-off-by: Junio C Hamano