We loop over the set of commits to merge, and for each one compute the
merge base against the existing set of merge base candidates we've
found. Then we replace the candidate set with a simple assignment of the
list head, leaking the old list. We should free it first before
assignment.
This makes t5521 leak-free, so mark it as such.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
alloc_nr, ALLOC_GROW, and ALLOC_GROW_BY are commonly used macros for
dynamic array allocation. Moving these macros to git-compat-util.h with
the other alloc macros focuses alloc.[ch] to allocation for Git objects
and additionally allows us to remove inclusions to alloc.h from files
that solely used the above macros.
Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is a leak that has existed since the method was first created
in fcb2c0769d (commit-reach: implement get_reachable_subset,
2018-11-02).
Signed-off-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Code clean-up around the use of the_repository.
* ab/remove-implicit-use-of-the-repository:
libs: use "struct repository *" argument, not "the_repository"
post-cocci: adjust comments for recent repo_* migration
cocci: apply the "revision.h" part of "the_repository.pending"
cocci: apply the "rerere.h" part of "the_repository.pending"
cocci: apply the "refs.h" part of "the_repository.pending"
cocci: apply the "promisor-remote.h" part of "the_repository.pending"
cocci: apply the "packfile.h" part of "the_repository.pending"
cocci: apply the "pretty.h" part of "the_repository.pending"
cocci: apply the "object-store.h" part of "the_repository.pending"
cocci: apply the "diff.h" part of "the_repository.pending"
cocci: apply the "commit.h" part of "the_repository.pending"
cocci: apply the "commit-reach.h" part of "the_repository.pending"
cocci: apply the "cache.h" part of "the_repository.pending"
cocci: add missing "the_repository" macros to "pending"
cocci: sort "the_repository" rules by header
cocci: fix incorrect & verbose "the_repository" rules
cocci: remove dead rule from "the_repository.pending.cocci"
"git for-each-ref" learns '%(ahead-behind:<base>)' that computes the
distances from a single reference point in the history with bunch
of commits in bulk.
* ds/ahead-behind:
commit-reach: add tips_reachable_from_bases()
for-each-ref: add ahead-behind format atom
commit-reach: implement ahead_behind() logic
commit-graph: introduce `ensure_generations_valid()`
commit-graph: return generation from memory
commit-graph: simplify compute_generation_numbers()
commit-graph: refactor compute_topological_levels()
for-each-ref: explicitly test no matches
for-each-ref: add --stdin option
As can easily be seen from grepping in our sources, we had these uses
of "the_repository" in various library code in cases where the
function in question was already getting a "struct repository *"
argument. Let's use that argument instead.
Out of these changes only the changes to "cache-tree.c",
"commit-reach.c", "shallow.c" and "upload-pack.c" would have cleanly
applied before the migration away from the "repo_*()" wrapper macros
in the preceding commits.
The rest aren't new, as we'd previously implicitly refer to
"the_repository", but it's now more obvious that we were doing the
wrong thing all along, and should have used the parameter instead.
The change to change "get_index_format_default(the_repository)" in
"read-cache.c" to use the "r" variable instead should arguably have
been part of [1], or in the subsequent cleanup in [2]. Let's do it
here, as can be seen from the initial code in [3] it's not important
that we use "the_repository" there, but would prefer to always use the
current repository.
This change excludes the "the_repository" use in "upload-pack.c"'s
upload_pack_advertise(), as the in-flight [4] makes that change.
1. ee1f0c242e (read-cache: add index.skipHash config option,
2023-01-06)
2. 6269f8eaad (treewide: always have a valid "index_state.repo"
member, 2023-01-17)
3. 7211b9e753 (repo-settings: consolidate some config settings,
2019-08-13)
4. <Y/hbUsGPVNAxTdmS@coredump.intra.peff.net>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Apply the part of "the_repository.pending.cocci" pertaining to
"commit.h".
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Apply the part of "the_repository.pending.cocci" pertaining to
"commit-reach.h".
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Both 'git for-each-ref --merged=<X>' and 'git branch --merged=<X>' use
the ref-filter machinery to select references or branches (respectively)
that are reachable from a set of commits presented by one or more
--merged arguments. This happens within reach_filter(), which uses the
revision-walk machinery to walk history in a standard way.
However, the commit-reach.c file is full of custom searches that are
more efficient, especially for reachability queries that can terminate
early when reachability is discovered. Add a new
tips_reachable_from_bases() method to commit-reach.c and call it from
within reach_filter() in ref-filter.c. This affects both 'git branch'
and 'git for-each-ref' as tested in p1500-graph-walks.sh.
For the Linux kernel repository, we take an already-fast algorithm and
make it even faster:
Test HEAD~1 HEAD
-------------------------------------------------------------------
1500.5: contains: git for-each-ref --merged 0.13 0.02 -84.6%
1500.6: contains: git branch --merged 0.14 0.02 -85.7%
1500.7: contains: git tag --merged 0.15 0.03 -80.0%
(Note that we remove the iterative 'git rev-list' test from p1500
because it no longer makes sense as a comparison to 'git for-each-ref'
and would just waste time running it for these comparisons.)
The algorithm is implemented in commit-reach.c in the method
tips_reachable_from_base(). This method takes a string_list of tips and
assigns the 'util' for each item with the value 1 if the base commit can
reach those tips.
Like other reachability queries in commit-reach.c, the fastest way to
search for "can A reach B?" is to do a depth-first search up to the
generation number of B, preferring to explore first parents before later
parents. While we must walk all reachable commits up to that generation
number when the answer is "no", the depth-first search can answer "yes"
much faster than other approaches in most cases.
This search becomes trickier when there are multiple targets for the
depth-first search. The commits with lower generation number are more
likely to be within the history of the start commit, but we don't want
to waste time searching commits of low generation number if the commit
target with lowest generation number has already been found.
The trick here is to take the input commits and sort them by generation
number in ascending order. Track the index within this order as
min_generation_index. When we find a commit, if its index in the list is
equal to min_generation_index, then we can increase the generation
number boundary of our search to the next-lowest value in the list.
With this mechanism, the number of commits to search is minimized with
respect to the depth-first search heuristic. We will walk all commits up
to the minimum generation number of a commit that is _not_ reachable
from the start, but we will walk only the necessary portion of the
depth-first search for the reachable commits of lower generation.
Add extra tests for this behavior in t6600-test-reach.sh as the
interesting data shape of that repository can sometimes demonstrate
corner case bugs.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Fully implement the commit-counting logic required to determine
ahead/behind counts for a batch of commit pairs. This is a new library
method within commit-reach.h. This method will be linked to the
for-each-ref builtin in the next change.
The interface for ahead_behind() uses two arrays. The first array of
commits contains the list of all starting points for the walk. This
includes all tip commits _and_ base commits. The second array specifies
base/tip pairs by pointing to commits within the first array, by index.
The second array also stores the resulting ahead/behind counts for each
of these pairs.
This implementation of ahead_behind() allows multiple bases, if desired.
Even with multiple bases, there is only one commit walk used for
counting the ahead/behind values, saving time when the base/tip ranges
overlap significantly.
This interface for ahead_behind() also makes it very easy to call
ensure_generations_valid() on the entire array of bases and tips. This
call is necessary because it is critical that the walk that counts
ahead/behind values never walks a commit more than once. Without
generation numbers on every commit, there is a possibility that a
commit date skew could cause the walk to revisit a commit and then
double-count it. For this reason, it is strongly recommended that 'git
ahead-behind' is only run in a repository with a commit-graph file that
covers most of the reachable commits, storing precomputed generation
numbers. If no commit-graph exists, this walk will be much slower as it
must walk all reachable commits in ensure_generations_valid() before
performing the counting logic.
It is possible to detect if generation numbers are available at run time
and redirect the implementation to another algorithm that does not
require this property. However, that implementation requires a commit
walk per base/tip pair _and_ can be slower due to the commit date
heuristics required. Such an implementation could be considered in the
future if there is a reason to include it, but most Git hosts should
already be generating a commit-graph file as part of repository
maintenance. Most Git clients should also be generating commit-graph
files as part of background maintenance or automatic GCs.
Now, let's discuss the ahead/behind counting algorithm.
The first array of commits are considered the starting commits. The
index within that array will play a critical role.
We create a new commit slab that maps commits to a bitmap. For a given
commit (anywhere in the history), its bitmap stores information relative
to which of the input commits can reach that commit. The ith bit will be
on if the ith commit from the starting list can reach that commit. It is
important to notice that these bitmaps are not the typical "reachability
bitmaps" that are stored in .bitmap files. Instead of signalling which
objects are reachable from the current commit, they instead signal
"which starting commits can reach me?" It is also important to know that
the bitmap is not necessarily "complete" until we walk that commit. We
will perform a commit walk by generation number in such a way that we
can guarantee the bitmap is correct when we visit that commit.
At the beginning of the ahead_behind() method, we initialize the bitmaps
for each of the starting commits. By enabling the ith bit for the ith
starting commit, we signal "the ith commit can reach itself."
We walk commits by popping the commit with maximum generation number out
of the queue, guaranteeing that we will never walk a child of that
commit in any future steps.
As we walk, we load the bitmap for the current commit and perform two
main steps. The _second_ step examines each parent of the current commit
and adds the current commit's bitmap bits to each parent's bitmap. (We
create a new bitmap for the parent if this is our first time seeing that
parent.) After adding the bits to the parent's bitmap, the parent is
added to the walk queue. Due to this passing of bits to parents, the
current commit has a guarantee that the ith bit is enabled on its bitmap
if and only if the ith commit can reach the current commit.
The first step of the walk is to examine the bitmask on the current
commit and decide which ranges the commit is in or not. Due to the "bit
pushing" in the second step, we have a guarantee that the ith bit of the
current commit's bitmap is on if and only if the ith starting commit can
reach it. For each ahead_behind_count struct, check the base_index and
tip_index to see if those bits are enabled on the current bitmap. If
exactly one bit is enabled, then increment the corresponding 'ahead' or
'behind' count. This increment is the reason we _absolutely need_ to
walk commits at most once.
The only subtle thing to do with this walk is to check to see if a
parent has all bits on in its bitmap, in which case it becomes "stale"
and is marked with the STALE bit. This allows queue_has_nonstale() to be
the terminating condition of the walk, which greatly reduces the number
of commits walked if all of the commits are nearby in history. It avoids
walking a large number of common commits when there is a deep history.
We also use the helper method insert_no_dup() to add commits to the
priority queue without adding them multiple times. This uses the PARENT2
flag. Thus, we must clear both the STALE and PARENT2 bits of all
commits, in case ahead_behind() is called multiple times in the same
process.
Co-authored-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Fix a segfaulting loop. The function and its caller may need
further clean-up.
* ew/commit-reach-clean-up-flags-fix:
commit-reach: avoid NULL dereference
This allows us to replace includes of cache.h with includes of the much
smaller alloc.h in many places. It does mean that we also need to add
includes of alloc.h in a number of C files.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The loop at the top of can_all_from_reach_with_flag() already
accounts for `from->objects[i].item' being NULL, so it follows
the cleanup loop should also account for a NULL `from_one'.
I managed to segfault here on one of my giant, many-remote repos
using `git fetch --negotiation-tip=... --negotiation-only'
where the --negotiation-tip= argument was a glob which (inadvertently)
captured more refs than I wanted. I have not reproduced this
in a standalone test case.
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a semantic patch for replace ALLOC_ARRAY+COPY_ARRAY with DUP_ARRAY
to reduce code duplication and apply its results.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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 <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The remove_redundant_with_gen() algorithm performs a depth-first-search
to find commits in the 'array' list, starting at the parents of each
commit in 'array'. The result is that commits in 'array' are marked
STALE when they are reachable from another commit in 'array'.
This depth-first-search is fast when commits lie on or near the
first-parent history of the higher commits. The search terminates early
if all but one commit becomes marked STALE.
However, it is possible that there are two independent commits with high
generation number. In that case, the depth-first-search might languish
by searching in lower generations due to the fixed min_generation used
throughout the method.
With the expectation that commits with lower generation are expected to
become STALE more often, we can optimize further by increasing that
min_generation boundary upon discovery of the commit with minimum
generation.
We must first sort the commits in 'array' by generation. We cannot sort
'array' itself since it must preserve relative order among the returned
results (see revision.c:mark_redundant_parents() for an example).
This simplifies the initialization of min_generation, but it also allows
us to increase the new min_generation when we find the commit with
smallest generation remaining.
This requires more than two commits in order to test, so I used the
Linux kernel repository with a few commits that are slightly off of the
first-parent history. I timed the following command:
git merge-base --independent 2ecedd756908 d2360a398f0b \
1253935ad801 160bab43419e 0e2209629fec 1d0e16ac1a9e
The first two commits have similar generation and are near the v5.10
tag. Commit 160bab43419e is off of the first-parent history behind v5.5,
while the others are scattered somewhere reachable from v5.9. This is
designed to demonstrate the optimization, as that commit within v5.5
would normally cause a lot of extra commit walking.
Since remove_redundant_with_alg() is called only when at least one of
the input commits has a finite generation number, this algorithm is
tested with a commit-graph generated starting at a number of different
tags, the earliest being v5.5.
commit-graph at v5.5:
| Method | Time |
|-----------------------+-------|
| *_no_gen() | 864ms |
| *_with_gen() (before) | 858ms |
| *_with_gen() (after) | 810ms |
commit-graph at v5.7:
| Method | Time |
|-----------------------+-------|
| *_no_gen() | 625ms |
| *_with_gen() (before) | 572ms |
| *_with_gen() (after) | 517ms |
commit-graph at v5.9:
| Method | Time |
|-----------------------+-------|
| *_no_gen() | 268ms |
| *_with_gen() (before) | 224ms |
| *_with_gen() (after) | 202ms |
commit-graph at v5.10:
| Method | Time |
|-----------------------+-------|
| *_no_gen() | 72ms |
| *_with_gen() (before) | 37ms |
| *_with_gen() (after) | 9ms |
Note that these are only modest improvements for the case where the two
independent commits are not in the commit-graph (not until v5.10). All
algorithms get faster as more commits are indexed, which is not a
surprise. However, the cost of walking extra commits is more and more
prevalent in relative terms as more commits are indexed. Finally, the
last case allows us to jump to the minimum generation between the last
two commits (that are actually independent) so we greatly reduce the
cost in that case.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Reachability algorithms in commit-reach.c frequently benefit from using
the first-parent history as a heuristic for satisfying reachability
queries. The most obvious example was implemented in 4fbcca4e
(commit-reach: make can_all_from_reach... linear, 2018-07-20).
Update the walk in remove_redundant() to use this same heuristic. Here,
we are walking starting at the parents of the input commits. Sort those
parents and walk from the highest generation to lower. Each time, use
the heuristic of searching the first parent history before continuing to
expand the walk.
The order in which we explore the commits matters, so update
compare_commits_by_gen to break generation number ties with commit date.
This has no effect when the commits are in a commit-graph file with
corrected commit dates computed, but it will assist when the commits are
in the region "above" the commit-graph with "infinite" generation
number. Note that we cannot shift to use
compare_commits_by_gen_then_commit_date as the method prototype is
different. We use compare_commits_by_gen for QSORT() as opposed to as a
priority function.
The important piece is to ensure we short-circuit the walk when we find
that there is a single non-redundant commit. This happens frequently
when looking for merge-bases or comparing several tags with 'git
merge-base --independent'. Use a new count 'count_still_independent' and
if that hits 1 we can stop walking.
To update 'count_still_independent' properly, we add use of the RESULT
flag on the input commits. Then we can detect when we reach one of these
commits and decrease the count. We need to remove the RESULT flag at
that moment because we might re-visit that commit when popping the
stack.
We use the STALE flag to mark parents that have been added to the new
walk_start list, but we need to clear that flag before we start walking
so those flags don't halt our depth-first-search walk.
On my copy of the Linux kernel repository, the performance of 'git
merge-base --independent <all-tags>' goes from 1.1 seconds to 0.11
seconds.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Move this earlier in the file so it can be used by more methods.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The current implementation of remove_redundant() uses several calls to
paint_down_to_common() to determine that commits are independent of each
other. This leads to quadratic behavior when many inputs are passed to
commands such as 'git merge-base'.
For example, in the Linux kernel repository, I tested the performance
by passing all tags:
git merge-base --independent $(git for-each-ref refs/tags --format="$(refname)")
(Note: I had to delete the tags v2.6.11-tree and v2.6.11 as they do
not point to commits.)
Here is the performance improvement introduced by this change:
Before: 16.4s
After: 1.1s
This performance improvement requires the commit-graph file to be
present. We keep the old algorithm around as remove_redundant_no_gen()
and use it when generation_numbers_enabled() is false. This is similar
to other algorithms within commit-reach.c. The new algorithm is
implemented in remove_redundant_with_gen().
The basic approach is to do one commit walk instead of many. First, scan
all commits in the list and mark their _parents_ with the STALE flag.
This flag will indicate commits that are reachable from one of the
inputs, except not including themselves. Then, walk commits until
covering all commits up to the minimum generation number pushing the
STALE flag throughout.
At the end, we need to clear the STALE bit from all of the commits
we walked. We move the non-stale commits in 'array' to the beginning of
the list, and this might overwrite stale commits. However, we store an
array of commits that started the walk, and use clear_commit_marks() on
each of those starting commits. That method will walk the reachable
commits with the STALE bit and clear them all. This makes the algorithm
safe for re-entry or for other uses of those commits after this walk.
This logic is covered by tests in t6600-test-reach.sh, so the behavior
does not change. This is tested both in the case with a commit-graph and
without.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Remove a comment at the beggining of remove_redundant() that mentions a
reordering of the input array to have the initial segment be the
independent commits and the final segment be the redundant commits.
While this behavior is followed in remove_redundant(), no callers rely
on that behavior.
Remove the final loop that copies this final segment and update the
comment to match the new behavior.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
091f4cf (commit: don't use generation numbers if not needed,
2018-08-30) changed paint_down_to_common() to use commit dates instead
of generation numbers v1 (topological levels) as the performance
regressed on certain topologies. With generation number v2 (corrected
commit dates) implemented, we no longer have to rely on commit dates and
can use generation numbers.
For example, the command `git merge-base v4.8 v4.9` on the Linux
repository walks 167468 commits, taking 0.135s for committer date and
167496 commits, taking 0.157s for corrected committer date respectively.
While using corrected commit dates, Git walks nearly the same number of
commits as commit date, the process is slower as for each comparision we
have to access a commit-slab (for corrected committer date) instead of
accessing struct member (for committer date).
This change incidentally broke the fragile t6404-recursive-merge test.
t6404-recursive-merge sets up a unique repository where all commits have
the same committer date without a well-defined merge-base.
While running tests with GIT_TEST_COMMIT_GRAPH unset, we use committer
date as a heuristic in paint_down_to_common(). 6404.1 'combined merge
conflicts' merges commits in the order:
- Merge C with B to form an intermediate commit.
- Merge the intermediate commit with A.
With GIT_TEST_COMMIT_GRAPH=1, we write a commit-graph and subsequently
use the corrected committer date, which changes the order in which
commits are merged:
- Merge A with B to form an intermediate commit.
- Merge the intermediate commit with C.
While resulting repositories are equivalent, 6404.4 'virtual trees were
processed' fails with GIT_TEST_COMMIT_GRAPH=1 as we are selecting
different merge-bases and thus have different object ids for the
intermediate commits.
As this has already causes problems (as noted in 859fdc0 (commit-graph:
define GIT_TEST_COMMIT_GRAPH, 2018-08-29)), we disable commit graph
within t6404-recursive-merge.
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In a preparatory step for introducing corrected commit dates, let's
return timestamp_t values from commit_graph_generation(), use
timestamp_t for local variables and define GENERATION_NUMBER_INFINITY
as (2 ^ 63 - 1) instead.
We rename GENERATION_NUMBER_MAX to GENERATION_NUMBER_V1_MAX to
represent the largest topological level we can store in the commit data
chunk.
With corrected commit dates implemented, we will have two such *_MAX
variables to denote the largest offset and largest topological level
that can be stored.
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Way back in f9b8908b (commit.c: use generation numbers for
in_merge_bases(), 2018-05-01), a heuristic was used to short-circuit
the in_merge_bases() walk. This works just fine as long as the
caller is checking only two commits, but when there are multiple,
there is a possibility that this heuristic is _very wrong_.
Some code moves since then has changed this method to
repo_in_merge_bases_many() inside commit-reach.c. The heuristic
computes the minimum generation number of the "reference" list, then
compares this number to the generation number of the "commit".
In a recent topic, a test was added that used in_merge_bases_many()
to test if a commit was reachable from a number of commits pulled
from a reflog. However, this highlighted the problem: if any of the
reference commits have a smaller generation number than the given
commit, then the walk is skipped _even if there exist some with
higher generation number_.
This heuristic is wrong! It must check the MAXIMUM generation number
of the reference commits, not the MINIMUM.
This highlights a testing gap. t6600-test-reach.sh covers many
methods in commit-reach.c, including in_merge_bases() and
get_merge_bases_many(), but since these methods either restrict to
two input commits or actually look for the full list of merge bases,
they don't check this heuristic!
Add a possible input to "test-tool reach" that tests
in_merge_bases_many() and add tests to t6600-test-reach.sh that
cover this heuristic. This includes cases for the reference commits
having generation above and below the generation of the input commit,
but also having maximum generation below the generation of the input
commit.
The fix itself is to swap min_generation with a max_generation in
repo_in_merge_bases_many().
Reported-by: Srinidhi Kaushik <shrinidhi.kaushik@gmail.com>
Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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
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 <dstolee@microsoft.com>
Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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 <l.s.r@web.de>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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 <abhishekkumar8222@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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 <abhishekkumar8222@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
| 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 <A> and <B> are swapped. However,
can_all_from_reach() will return immediately if the generation numbers
show that <A> has larger generation number than <B>. Thus, the time for
the swapped case is universally 0.004s in each case.
Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reported-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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 <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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
<url> has a submodule. Note that --recurse-submodules is not needed to
demonstrate the bug.
$ git clone <url> 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 <hash1> for commit <hash2>
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 <johannes.schindelin@gmx.de>
Helped-by: Jeff King <peff@peff.net>
Helped-by: Szeder Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The in-core repository instances are passed through more codepaths.
* sb/more-repo-in-api: (23 commits)
t/helper/test-repository: celebrate independence from the_repository
path.h: make REPO_GIT_PATH_FUNC repository agnostic
commit: prepare free_commit_buffer and release_commit_memory for any repo
commit-graph: convert remaining functions to handle any repo
submodule: don't add submodule as odb for push
submodule: use submodule repos for object lookup
pretty: prepare format_commit_message to handle arbitrary repositories
commit: prepare logmsg_reencode to handle arbitrary repositories
commit: prepare repo_unuse_commit_buffer to handle any repo
commit: prepare get_commit_buffer to handle any repo
commit-reach: prepare in_merge_bases[_many] to handle any repo
commit-reach: prepare get_merge_bases to handle any repo
commit-reach.c: allow get_merge_bases_many_0 to handle any repo
commit-reach.c: allow remove_redundant to handle any repo
commit-reach.c: allow merge_bases_many to handle any repo
commit-reach.c: allow paint_down_to_common to handle any repo
commit: allow parse_commit* to handle any repo
object: parse_object to honor its repository argument
object-store: prepare has_{sha1, object}_file to handle any repo
object-store: prepare read_object_file to deal with any repo
...
Similarly to previous patches, the get_merge_base functions are used
often in the code base, which makes migrating them hard.
Implement the new functions, prefixed with 'repo_' and hide the old
functions behind a wrapper macro.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As the function is file local and not widely used, migrate it all at once.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The existing reachability algorithms in commit-reach.c focus on
finding merge-bases or determining if all commits in a set X can
reach at least one commit in a set Y. However, for two commits sets
X and Y, we may also care about which commits in Y are reachable
from at least one commit in X.
Implement get_reachable_subset() which answers this question. Given
two arrays of commits, 'from' and 'to', return a commit_list with
every commit from the 'to' array that is reachable from at least
one commit in the 'from' array.
The algorithm is a simple walk starting at the 'from' commits, using
the PARENT2 flag to indicate "this commit has already been added to
the walk queue". By marking the 'to' commits with the PARENT1 flag,
we can determine when we see a commit from the 'to' array. We remove
the PARENT1 flag as we add that commit to the result list to avoid
duplicates.
The order of the resulting list is a reverse of the order that the
commits are discovered in the walk.
There are a couple shortcuts to avoid walking more than we need:
1. We determine the minimum generation number of commits in the
'to' array. We do not walk commits with generation number
below this minimum.
2. We count how many distinct commits are in the 'to' array, and
decrement this count when we discover a 'to' commit during the
walk. If this number reaches zero, then we can terminate the
walk.
Tests will be added using the 'test-tool reach' helper in a
subsequent commit.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The elements of the array to be sorted are commit pointers, so the
comparison function gets handed references to these pointers, not
pointers to commit objects. Cast to the right type and dereference
once to correctly get the commit reference.
Found using Clang's ASan and t5500.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The algorithm in can_all_from_reach_with_flags() performs a depth-
first-search, terminated by generation number, intending to use
a hueristic that "important" commits are found in the first-parent
history. This heuristic is valuable in scenarios like fetch
negotiation.
However, there is a problem! After the search finds a target commit,
it should pop all commits off the stack and mark them as "can reach".
This logic is incorrect, so the algorithm instead walks all reachable
commits above the generation-number cutoff.
The existing algorithm is still an improvement over the previous
algorithm, as the worst-case complexity went from quadratic to linear.
The performance measurement at the time was good, but not dramatic.
By fixing this heuristic, we reduce the number of walked commits.
We can also re-run the performance tests from commit 4fbcca4e
"commit-reach: make can_all_from_reach... linear".
Performance was measured on the Linux repository using
'test-tool reach can_all_from_reach'. The input included rows seeded by
tag values. The "small" case included X-rows as v4.[0-9]* and Y-rows as
v3.[0-9]*. This mimics a (very large) fetch that says "I have all major
v3 releases and want all major v4 releases." The "large" case included
X-rows as "v4.*" and Y-rows as "v3.*". This adds all release-candidate
tags to the set, which does not greatly increase the number of objects
that are considered, but does increase the number of 'from' commits,
demonstrating the quadratic nature of the previous code.
Small Case:
4fbcca4e~1: 0.85 s
4fbcca4e: 0.26 s (num_walked: 1,011,035)
HEAD: 0.14 s (num_walked: 8,601)
Large Case:
4fbcca4e~1: 24.0 s
4fbcca4e: 0.12 s (num_walked: 503,925)
HEAD: 0.06 s (num_walked: 217,243)
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We added faster equality-comparison functions for hashes in
14438c4497 (introduce hasheq() and oideq(), 2018-08-28). A
few topics were in-flight at the time, and can now be
converted. This covers all spots found by "make coccicheck"
in master (the coccicheck results were tweaked by hand for
style).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Due to a regression introduced by 4fbcca4e "commit-reach: make
can_all_from_reach... linear" the series including b67f6b26
"commit-reach: properly peel tags" was merged to master quickly.
There were a few more cleanups left to apply in the series, which
are included by this change:
1. Clean up a comment that is in the incorrect style.
2. Replace multiple calls to clear_commit_marks() with one call to
clear_commit_marks_many().
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
