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This is another simple change with a long explanation...
merge-recursive and merge-ort are both based on the same recursive idea:
if there is more than one merge base, merge the merge bases (which may
require first merging the merge bases of the merges bases, etc.). The
depth of the inner merge is recorded via a variable called "call_depth",
which we'll bring up again later. Naturally, the inner merges
themselves can have conflicts and various messages generated about those
files.
merge-recursive immediately prints to stdout as it goes, at the risk of
printing multiple conflict notices for the same path separated far apart
from each other with many intervenining conflict notices for other paths
between them. And this is true even if there are no inner merges
involved. An example of this was given in [1] and apparently caused
some confusion:
CONFLICT (rename/add): Rename A->B in HEAD. B added in otherbranch
...dozens of conflicts for OTHER paths...
CONFLICT (content): Merge conflicts in B
In contrast, merge-ort collects messages and stores them by path so that
it can print them grouped by path. Thus, the same case handled by
merge-ort would have output of the form:
CONFLICT (rename/add): Rename A->B in HEAD. B added in otherbranch
CONFLICT (content): Merge conflicts in B
...dozens of conflicts for OTHER paths...
This is generally helpful, but does make a separate bug more
problematic. In particular, while merge-recursive might report the
following for a recursive merge:
Auto-merging dir.c
Auto-merging midx.c
CONFLICT (content): Merge conflict in midx.c
Auto-merging diff.c
Auto-merging dir.c
CONFLICT (content): Merge conflict in dir.c
merge-ort would instead report:
Auto-merging diff.c
Auto-merging dir.c
Auto-merging dir.c
CONFLICT (content): Merge conflict in dir.c
Auto-merging midx.c
CONFLICT (content): Merge conflict in midx.c
The fact that messages for the same file are together is probably
helpful in general, but with the indentation missing for the inner
merge it unfortunately serves to confuse. This probably would lead
users to wonder:
* Why is Git reporting that "dir.c" is being merged twice?
* If midx.c has conflicts, why do I not see any when I open up the
file and why are no conflicts shown in the index?
Fix this output confusion by changing the output to clearly
differentiate the messages for outer merges from the ones for inner
merges, changing the above output from merge-ort to:
Auto-merging diff.c
From inner merge: Auto-merging dir.c
Auto-merging dir.c
CONFLICT (content): Merge conflict in dir.c
From inner merge: Auto-merging midx.c
From inner merge: CONFLICT (content): Merge conflict in midx.c
(Note: the number of spaces after the 'From inner merge:' is
2*call_depth).
One other thing to note here, that I didn't notice until typing up this
commit message, is that merge-recursive does not print any messages from
the inner merges by default; the extra verbosity has to be requested.
merge-ort currently has no verbosity controls and always prints these.
We may also want to change that, but for now, just make the output
clearer with these extra markings and indentation.
[1] https://lore.kernel.org/git/CAGyf7-He4in8JWUh9dpAwvoPkQz9hr8nCBpxOxhZEd8+jtqTpg@mail.gmail.com/
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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"git log --remerge-diff" shows the difference from mechanical merge
result and the result that is actually recorded in a merge commit.
* en/remerge-diff:
diff-merges: avoid history simplifications when diffing merges
merge-ort: mark conflict/warning messages from inner merges as omittable
show, log: include conflict/warning messages in --remerge-diff headers
diff: add ability to insert additional headers for paths
merge-ort: format messages slightly different for use in headers
merge-ort: mark a few more conflict messages as omittable
merge-ort: capture and print ll-merge warnings in our preferred fashion
ll-merge: make callers responsible for showing warnings
log: clean unneeded objects during `log --remerge-diff`
show, log: provide a --remerge-diff capability
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Leakfix.
* en/plug-leaks-in-merge:
merge: fix memory leaks in cmd_merge()
merge-ort: fix memory leak in merge_ort_internal()
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The merge-ort misbehaved when merge.renameLimit configuration is
set too low and failed to find all renames.
* en/merge-ort-restart-optim-fix:
merge-ort: avoid assuming all renames detected
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A recursive merge involves merging the merge bases of the two branches
being merged. Such an inner merge can itself generate conflict notices.
While such notices may be useful when initially trying to create a
merge, they seem to just be noise when investigating merges later with
--remerge-diff. (Especially when both sides of the outer merge resolved
the conflict the same way leading to no overall conflict.) Remove them.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Conflicts such as modify/delete, rename/rename, or file/directory are
not representable via content conflict markers, and the normal output
messages notifying users about these were dropped with --remerge-diff.
While we don't want these messages randomly shown before the commit
and diff headers, we do want them to still be shown; include them as
part of the diff headers instead.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When users run
git show --remerge-diff $MERGE_COMMIT
or
git log -p --remerge-diff ...
stdout is not an appropriate location to dump conflict messages, but we
do want to provide them to users. We will include them in the diff
headers instead...but for that to work, we need for any multiline
messages to replace newlines with both a newline and a space. Add a new
flag to signal when we want these messages modified in such a fashion,
and use it in path_msg() to modify these messages this way. Also, allow
a special prefix to be specified for these headers.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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path_msg() has the ability to mark messages as omittable, designed for
remerge-diff where we'll instead be showing conflict messages as diff
headers for a subsequent diff. While all these messages are very useful
when trying to create a merge initially, early use with the
--remerge-diff feature (the only user of this omittable conflict message
capability), suggests that the particular messages marked in this commit
are just noise when trying to see what changes users made to create a
merge commit. Mark them as omittable.
Note that there were already a few messages marked as omittable in
merge-ort when doing a remerge-diff, because the development of
--remerge-diff preceded the upstreaming of merge-ort and I was trying to
ensure merge-ort could handle all the necessary requirements. See
commit c5a6f65527 ("merge-ort: add modify/delete handling and delayed
output processing", 2020-12-03) for the initial details. For some
examples of already-marked-as-omittable messages, see either
"Auto-merging <path>" or some of the submodule update hints. This
commit just adds two more messages that should also be omittable.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Instead of immediately printing ll-merge warnings to stderr, we save
them in our output strbuf. Besides allowing us to move these warnings
to a special file for --remerge-diff, this has two other benefits for
regular merges done by merge-ort:
* The deferral of messages ensures we can print all messages about
any given path together (merge-recursive was known to sometimes
intersperse messages about other paths, particularly when renames
were involved).
* The deferral of messages means we can avoid printing spurious
conflict messages when we just end up aborting due to local user
modifications in the way. (In contrast to merge-recursive.c which
prematurely checks for local modifications in the way via
unpack_trees() and gets the check wrong both in terms of false
positives and false negatives relative to renames, merge-ort does
not perform the local modifications in the way check until the
checkout() step after the full merge has been computed.)
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Since some callers may want to send warning messages to somewhere other
than stdout/stderr, stop printing "warning: Cannot merge binary files"
from ll-merge and instead modify the return status of ll_merge() to
indicate when a merge of binary files has occurred. Message printing
probably does not belong in a "low-level merge" anyway.
This commit continues printing the message as-is, just from the callers
instead of within ll_merge(). Future changes will start handling the
message differently in the merge-ort codepath.
There was one special case here: the callers in rerere.c do NOT check
for and print such a message; since those code paths explicitly skip
over binary files, there is no reason to check for a return status of
LL_MERGE_BINARY_CONFLICT or print the related message.
Note that my methodology included first modifying ll_merge() to return
a struct, so that the compiler would catch all the callers for me and
ensure I had modified all of them. After modifying all of them, I then
changed the struct to an enum.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The documentation for merge_incore_recursive(), modelled after
merge_recursive(), notes that
merge_bases will be consumed (emptied) so make a copy if you need it
However, in merge_ort_internal() (which merge_incore_recursive() calls),
it runs
merged_merge_bases = pop_commit(&merge_bases);
...
for (iter = merge_bases; iter; iter = iter->next) {
...
}
In other words, it only consumes the *first* entry of merge_bases, and
the rest it iterates through. If it iterated through all of them, the
caller could be responsible for free'ing the memory. If it consumed all
of them, the current documentation would be correct and the callers
would need to do nothing. The current middle ground makes it impossible
for callers to avoid memory leaks, since any attempt to use the
merge_bases it passes in would result in a use-after-free.
It turns out this part of the code was copied from merge-recursive.c,
which has had the same bug for 15.5 years. However, since we are trying
to keep merge-recursive.c stable as we sunset it, let's just fix the
leak in in merge_ort_internal() by having it actually consume all the
elements of the merge_bases commit_list.
Testing this commit against t6404 (the first testcase specifically
about recursive merges) under valgrind shows that this patch fixes
the following leak:
32 (16 direct, 16 indirect) bytes in 1 blocks are definitely lost \
in loss record 49 of 126
at 0x484086F: malloc (vg_replace_malloc.c:380)
by 0x69FFEB: do_xmalloc (wrapper.c:41)
by 0x6A0073: xmalloc (wrapper.c:62)
by 0x52A72D: commit_list_insert (commit.c:556)
by 0x47EC86: try_merge_strategy (merge.c:751)
by 0x48143B: cmd_merge (merge.c:1679)
by 0x40686E: run_builtin (git.c:464)
by 0x406C51: handle_builtin (git.c:716)
by 0x406E96: run_argv (git.c:783)
by 0x40730A: cmd_main (git.c:914)
by 0x4E7DFA: main (common-main.c:56)
Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In commit 8b09a900a1 ("merge-ort: restart merge with cached renames to
reduce process entry cost", 2021-07-16), we noted that in the merge-ort
steps of
collect_merge_info()
detect_and_process_renames()
process_entries()
that process_entries() was expensive, and we could often make it cheaper
by changing this to
collect_merge_info()
detect_and_process_renames()
<cache all the renames, and restart>
collect_merge_info()
detect_and_process_renames()
process_entries()
because the second collect_merge_info() would be cheaper (we could avoid
traversing into some directories), the second
detect_and_process_renames() would be free since we had already detected
all renames, and then process_entries() has far fewer entries to handle.
However, this was built on the assumption that the first
detect_and_process_renames() actually detected all potential renames.
If someone has merge.renameLimit set to some small value, that
assumption is violated which manifests later with the following message:
$ git -c merge.renameLimit=1 rebase upstream
...
git: merge-ort.c:546: clear_or_reinit_internal_opts: Assertion
`renames->cached_pairs_valid_side == 0' failed.
Turn off this cache-renames-and-restart whenever we cannot detect all
renames, and add a testcase that would have caught this problem.
Reported-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Tested-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Ever since commit a492d5331c ("merge-ort: ensure we consult df_conflict
and path_conflicts", 2021-06-30), when renormalization is active AND a
file is involved in a rename/delete conflict BUT the file is unmodified
(either before or after renormalization), merge-ort was running into an
assertion failure. Prior to that commit (or if assertions were compiled
out), merge-ort would mis-merge instead, ignoring the rename/delete
conflict and just deleting the file.
Remove the assertions, fix the code appropriately, leave some good
comments in the code, and add a testcase for this situation.
Reported-by: Ralf Thielow <ralf.thielow@gmail.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Follow through the work to use the repo interface to access
submodule objects in-process, instead of abusing the alternate
object database interface.
* jt/no-abuse-alternate-odb-for-submodules:
submodule: trace adding submodule ODB as alternate
submodule: pass repo to check_has_commit()
object-file: only register submodule ODB if needed
merge-{ort,recursive}: remove add_submodule_odb()
refs: peeling non-the_repository iterators is BUG
refs: teach arbitrary repo support to iterators
refs: plumb repo into ref stores
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Various fixes in code paths that move untracked files away to make room.
* en/removing-untracked-fixes:
Documentation: call out commands that nuke untracked files/directories
Comment important codepaths regarding nuking untracked files/dirs
unpack-trees: avoid nuking untracked dir in way of locally deleted file
unpack-trees: avoid nuking untracked dir in way of unmerged file
Change unpack_trees' 'reset' flag into an enum
Remove ignored files by default when they are in the way
unpack-trees: make dir an internal-only struct
unpack-trees: introduce preserve_ignored to unpack_trees_options
read-tree, merge-recursive: overwrite ignored files by default
checkout, read-tree: fix leak of unpack_trees_options.dir
t2500: add various tests for nuking untracked files
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After the parent commit and some of its ancestors, the only place
commits are being accessed through alternates is in the user-facing
message formatting code. Fix those, and remove the add_submodule_odb()
calls.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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More code paths that use the hack to add submodule's object
database to the set of alternate object store have been cleaned up.
* jt/add-submodule-odb-clean-up:
revision: remove "submodule" from opt struct
repository: support unabsorbed in repo_submodule_init
submodule: remove unnecessary unabsorbed fallback
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Typofixes.
* en/typofixes:
merge-ort: fix completely wrong comment
trace2.h: fix trivial comment typo
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Change several commands to remove ignored files by default when they are
in the way. Since some commands (checkout, merge) take a
--no-overwrite-ignore option to allow the user to configure this, and it
may make sense to add that option to more commands (and in the case of
merge, actually plumb that configuration option through to more of the
backends than just the fast-forwarding special case), add little
comments about where such flags would be used.
Incidentally, this fixes a test failure in t7112.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Currently, every caller of unpack_trees() that wants to ensure ignored
files are overwritten by default needs to:
* allocate unpack_trees_options.dir
* flip the DIR_SHOW_IGNORED flag in unpack_trees_options.dir->flags
* call setup_standard_excludes
AND then after the call to unpack_trees() needs to
* call dir_clear()
* deallocate unpack_trees_options.dir
That's a fair amount of boilerplate, and every caller uses identical
code. Make this easier by instead introducing a new boolean value where
the default value (0) does what we want so that new callers of
unpack_trees() automatically get the appropriate behavior. And move all
the handling of unpack_trees_options.dir into unpack_trees() itself.
While preserve_ignored = 0 is the behavior we feel is the appropriate
default, we defer fixing commands to use the appropriate default until a
later commit. So, this commit introduces several locations where we
manually set preserve_ignored=1. This makes it clear where code paths
were previously preserving ignored files when they should not have been;
a future commit will flip these to instead use a value of 0 to get the
behavior we want.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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jt/no-abuse-alternate-odb-for-submodules
* jt/add-submodule-odb-clean-up:
revision: remove "submodule" from opt struct
repository: support unabsorbed in repo_submodule_init
submodule: remove unnecessary unabsorbed fallback
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Various mergy operations have been prepared to work efficiently
with the sparse index.
* ds/mergies-with-sparse-index:
sparse-index: integrate with cherry-pick and rebase
sequencer: ensure full index if not ORT strategy
t1092: add cherry-pick, rebase tests
merge-ort: expand only for out-of-cone conflicts
merge: make sparse-aware with ORT
diff: ignore sparse paths in diffstat
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Not sure what happened, but the comment is describing code elsewhere in
the file. Fix the comment to actually discuss the code that follows.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Merge conflicts happen often enough to want to avoid expanding a sparse
index when they happen, as long as those conflicts are within the
sparse-checkout cone. If a conflict exists outside of the
sparse-checkout cone, then we still need to expand before iterating over
the index entries. This is critical to do in advance because of how the
original_cache_nr is tracked to allow inserting and replacing cache
entries.
Iterate over the conflicted files and check if any paths are outside of
the sparse-checkout cone. If so, then expand the full index.
Add a test that demonstrates that we do not expand the index, even when
we hit a conflict within the sparse-checkout cone.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Allow 'git merge' to operate without expanding a sparse index, at least
not immediately. The index still will be expanded in a few cases:
1. If the merge strategy is 'recursive', then we enable
command_requires_full_index at the start of the merge_recursive()
method. We expect sparse-index users to also have the 'ort' strategy
enabled.
2. With the 'ort' strategy, if the merge results in a conflicted file,
then we expand the index before updating the working tree. The loop
that iterates over the worktree replaces index entries and tracks
'origintal_cache_nr' which can become completely wrong if the index
expands in the middle of the operation. This safety valve is
important before that loop starts. A later change will focus this
to only expand if we indeed have a conflict outside of the
sparse-checkout cone.
3. Other merge strategies are executed as a 'git merge-X' subcommand,
and those strategies are currently protected with the
'command_requires_full_index' guard.
Some test updates are required, including a mistaken 'git checkout -b'
that did not specify the base branch, causing merges to be fast-forward
merges.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Clean up a TODO in revision.h by removing the "submodule" field from
struct setup_revision_opt. This field is only used to specify the ref
store to use, so use rev_info->repo to determine the ref store instead.
The only users of this field are merge-ort.c and merge-recursive.c.
However, both these files specify the superproject as rev_info->repo and
the submodule as setup_revision_opt->submodule. In order to be able to
pass the submodule as rev_info->repo, all commits must be parsed with
the submodule explicitly specified; this patch does that as well. (An
incremental solution in which only some commits are parsed with explicit
submodule will not work, because if the same commit is parsed twice in
different repositories, there will be 2 heap-allocated object structs
corresponding to that commit, and any flag set by the revision walking
mechanism on one of them will not be reflected onto the other.)
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Final batch for "merge -sort" optimization.
* en/ort-perf-batch-15:
merge-ort: remove compile-time ability to turn off usage of memory pools
merge-ort: reuse path strings in pool_alloc_filespec
merge-ort: store filepairs and filespecs in our mem_pool
diffcore-rename, merge-ort: add wrapper functions for filepair alloc/dealloc
merge-ort: switch our strmaps over to using memory pools
merge-ort: set up a memory pool
merge-ort: add pool_alloc, pool_calloc, and pool_strndup wrappers
diffcore-rename: use a mem_pool for exact rename detection's hashmap
merge-ort: rename str{map,intmap,set}_func()
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Further optimization on "merge -sort" backend.
* en/ort-perf-batch-14:
merge-ort: restart merge with cached renames to reduce process entry cost
merge-ort: avoid recursing into directories when we don't need to
merge-ort: defer recursing into directories when merge base is matched
merge-ort: add a handle_deferred_entries() helper function
merge-ort: add data structures for allowable trivial directory resolves
merge-ort: add some more explanations in collect_merge_info_callback()
merge-ort: resolve paths early when we have sufficient information
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Simplify code maintenance by removing the ability to toggle between
usage of memory pools and direct allocations. This allows us to also
remove paths_to_free since it was solely about bookkeeping to make sure
we freed the necessary paths, and allows us to remove some auxiliary
functions.
Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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pool_alloc_filespec() was written so that the code when pool != NULL
mimicked the code from alloc_filespec(), which including allocating
enough extra space for the path and then copying it. However, the path
passed to pool_alloc_filespec() is always going to already be in the
same memory pool, so we may as well reuse it instead of copying it.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 198.5 ms ± 3.4 ms 198.3 ms ± 2.9 ms
mega-renames: 679.1 ms ± 5.6 ms 661.8 ms ± 5.9 ms
just-one-mega: 271.9 ms ± 2.8 ms 264.6 ms ± 2.5 ms
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 198.1 ms ± 2.6 ms 198.5 ms ± 3.4 ms
mega-renames: 715.8 ms ± 4.0 ms 679.1 ms ± 5.6 ms
just-one-mega: 276.8 ms ± 4.2 ms 271.9 ms ± 2.8 ms
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We want to be able to allocate filespecs and filepairs using a mem_pool.
However, filespec data will still remain outside the pool (perhaps in
the future we could plumb the pool through the various diff APIs to
allocate the filespec data too, but for now we are limiting the scope).
Add some extra functions to allocate these appropriately based on the
non-NULL-ness of opt->priv->pool, as well as some extra functions to
handle correctly deallocating the relevant parts of them. A future
commit will make use of these new functions.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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For all the strmaps (including strintmaps and strsets) whose memory is
unconditionally freed as part of clear_or_reinit_internal_opts(), switch
them over to using our new memory pool.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 202.5 ms ± 3.2 ms 198.1 ms ± 2.6 ms
mega-renames: 1.072 s ± 0.012 s 715.8 ms ± 4.0 ms
just-one-mega: 357.3 ms ± 3.9 ms 276.8 ms ± 4.2 ms
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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merge-ort has a lot of data structures, and they all tend to be freed
together in clear_or_reinit_internal_opts(). Set up a memory pool to
allow us to make these allocations and deallocations faster. Future
commits will adjust various callers to make use of this memory pool.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Make the code more flexible so that it can handle both being run with or
without a memory pool by adding utility functions which will either call
xmalloc, xcalloc, xstrndup
or
mem_pool_alloc, mem_pool_calloc, mem_pool_strndup
depending on whether we have a non-NULL memory pool. A subsequent
commit will make use of these.
(We will actually be dropping these functions soon and just assuming we
always have a memory pool, but the flexibility was very useful during
development of merge-ort so I want to be able to restore it if needed.)
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In order to make it clearer that these three variables holding a
function refer to functions that will clear the strmap/strintmap/strset,
rename them to str{map,intmap,set}_clear_func().
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Documentation on "git diff -l<n>" and diff.renameLimit have been
updated, and the defaults for these limits have been raised.
* en/rename-limits-doc:
rename: bump limit defaults yet again
diffcore-rename: treat a rename_limit of 0 as unlimited
doc: clarify documentation for rename/copy limits
diff: correct warning message when renameLimit exceeded
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Many "printf"-like helper functions we have have been annotated
with __attribute__() to catch placeholder/parameter mismatches.
* ab/attribute-format:
advice.h: add missing __attribute__((format)) & fix usage
*.h: add a few missing __attribute__((format))
*.c static functions: add missing __attribute__((format))
sequencer.c: move static function to avoid forward decl
*.c static functions: don't forward-declare __attribute__
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The merge algorithm mostly consists of the following three functions:
collect_merge_info()
detect_and_process_renames()
process_entries()
Prior to the trivial directory resolution optimization of the last half
dozen commits, process_entries() was consistently the slowest, followed
by collect_merge_info(), then detect_and_process_renames(). When the
trivial directory resolution applies, it often dramatically decreases
the amount of time spent in the two slower functions.
Looking at the performance results in the previous commit, the trivial
directory resolution optimization helps amazingly well when there are no
relevant renames. It also helps really well when reapplying a long
series of linear commits (such as in a rebase or cherry-pick), since the
relevant renames may well be cached from the first reapplied commit.
But when there are any relevant renames that are not cached (represented
by the just-one-mega testcase), then the optimization does not help at
all.
Often, I noticed that when the optimization does not apply, it is
because there are a handful of relevant sources -- maybe even only one.
It felt frustrating to need to recurse into potentially hundreds or even
thousands of directories just for a single rename, but it was needed for
correctness.
However, staring at this list of functions and noticing that
process_entries() is the most expensive and knowing I could avoid it if
I had cached renames suggested a simple idea: change
collect_merge_info()
detect_and_process_renames()
process_entries()
into
collect_merge_info()
detect_and_process_renames()
<cache all the renames, and restart>
collect_merge_info()
detect_and_process_renames()
process_entries()
This may seem odd and look like more work. However, note that although
we run collect_merge_info() twice, the second time we get to employ
trivial directory resolves, which makes it much faster, so the increased
time in collect_merge_info() is small. While we run
detect_and_process_renames() again, all renames are cached so it's
nearly a no-op (we don't call into diffcore_rename_extended() but we do
have a little bit of data structure checking and fixing up). And the
big payoff comes from the fact that process_entries(), will be much
faster due to having far fewer entries to process.
This restarting only makes sense if we can save recursing into enough
directories to make it worth our while. Introduce a simple heuristic to
guide this. Note that this heuristic uses a "wanted_factor" that I have
virtually no actual real world data for, just some back-of-the-envelope
quasi-scientific calculations that I included in some comments and then
plucked a simple round number out of thin air. It could be that
tweaking this number to make it either higher or lower improves the
optimization. (There's slightly more here; when I first introduced this
optimization, I used a factor of 10, because I was completely confident
it was big enough to not cause slowdowns in special cases. I was
certain it was higher than needed. Several months later, I added the
rough calculations which make me think the optimal number is close to 2;
but instead of pushing to the limit, I just bumped it to 3 to reduce the
risk that there are special cases where this optimization can result in
slowing down the code a little. If the ratio of path counts is below 3,
we probably will only see minor performance improvements at best
anyway.)
Also, note that while the diffstat looks kind of long (nearly 100
lines), more than half of it is in two comments explaining how things
work.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 205.1 ms ± 3.8 ms 204.2 ms ± 3.0 ms
mega-renames: 1.564 s ± 0.010 s 1.076 s ± 0.015 s
just-one-mega: 479.5 ms ± 3.9 ms 364.1 ms ± 7.0 ms
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This combines the work of the last several patches, and implements the
conditions when we don't need to recurse into directories. It's perhaps
easiest to see the logic by separating the fact that a directory might
have both rename sources and rename destinations:
* rename sources: only files present in the merge base can serve as
rename sources, and only when one side deletes that file. When the
tree on one side matches the merge base, that means every file
within the subtree matches the merge base. This means that the
skip-irrelevant-rename-detection optimization from before kicks in
and we don't need any of these files as rename sources.
* rename destinations: the tree that does not match the merge base
might have newly added and hence unmatched destination files.
This is what usually prevents us from doing trivial directory
resolutions in the merge machinery. However, the fact that we have
deferred recursing into this directory until the end means we know
whether there are any unmatched relevant potential rename sources
elsewhere in this merge. If there are no unmatched such relevant
sources anywhere, then there is no need to look for unmatched
potential rename destinations to match them with.
This informs our algorithm:
* Search through relevant_sources; if we have entries, they better all
be reflected in cached_pairs or cached_irrelevant, otherwise they
represent an unmatched potential rename source (causing the
optimization to be disallowed).
* For any relevant_source represented in cached_pairs, we do need to
to make sure to get the destination for each source, meaning we need
to recurse into any ancestor directories of those destinations.
* Once we've recursed into all the rename destinations for any
relevant_sources in cached_pairs, we can then do the trivial
directory resolution for the remaining directories.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 5.235 s ± 0.042 s 205.1 ms ± 3.8 ms
mega-renames: 9.419 s ± 0.107 s 1.564 s ± 0.010 s
just-one-mega: 480.1 ms ± 3.9 ms 479.5 ms ± 3.9 ms
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When one side of history matches the merge base (including when the
merge base has no entry for the given directory), have
collect_merge_info_callback() defer recursing into the directory. To
ensure those entries are eventually handled, add a call to
handled_deferred_entries() in collect_merge_info() after
traverse_trees() returns.
Note that the condition in collect_merge_info_callback() may look more
complicated than necessary at first glance;
renames->trivial_merges_okay[side] is always true until
handle_deferred_entries() is called, and possible_trivial_merges[side]
is always empty right now (and in the future won't be filled until
handle_deferred_entries() is called). However, when
handle_deferred_entries() calls traverse_trees() for the relevant
deferred directories, those traverse_trees() calls will once again end
up in collect_merge_info_callback() for all the entries under those
subdirectories. The extra conditions are there for such deferred cases
and will be used more as we do more with those variables.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In order to allow trivial directory resolution, we first need to be able
to gather more information to determine if the optimization is safe. To
enable that, we need a way of deferring the recursion into the directory
until a later time. Naturally, deferring the entry into a subtree means
that we need some function that will later recurse into the subdirectory
exactly the same way that collect_merge_info_callback() would have done.
Add a helper function that does this. For now this function is not used
but a subsequent commit will change that. Future commits will also make
the function sometimes resolve directories instead of traversing inside.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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As noted a few commits ago, we can resolve individual files early if all
three sides of the merge have a file at the path and two of the three
sides match. We would really like to do the same thing with
directories, because being able to do a trivial directory resolve means
we don't have to recurse into the directory, potentially saving us a
huge amount of time in both collect_merge_info() and process_entries().
Unfortunately, resolving directories early would mean missing any
renames whose source or destination is underneath that directory.
If we somehow knew there weren't any renames under the directory in
question, then we could resolve it early. Sadly, it is impossible to
determine whether there are renames under the directory in question
without recursing into it, and this has traditionally kept us from ever
implementing such an optimization.
In commit f89b4f2bee ("merge-ort: skip rename detection entirely if
possible", 2021-03-11), we added an additional reason that rename
detection could be skipped entirely -- namely, if no *relevant* sources
were present. Without completing collect_merge_info_callback(), we do
not yet know if there are no relevant sources. However, we do know that
if the current directory on one side matches the merge base, then every
source file within that directory will not be RELEVANT_CONTENT, and a
few simple checks can often let us rule out RELEVANT_LOCATION as well.
This suggests we can just defer recursing into such directories until
the end of collect_merge_info.
Since the deferred directories are known to not add any relevant sources
due to the above properties, then if there are no relevant sources after
we've traversed all paths other than the deferred ones, then we know
there are not any relevant sources. Under those conditions, rename
detection is unnecessary, and that means we can resolve the deferred
directories without recursing into them.
Note that the logic for skipping rename detection was also modified
further in commit 76e253793c ("merge-ort, diffcore-rename: employ cached
renames when possible", 2021-01-30); in particular rename detection can
be skipped if we already have cached renames for each relevant source.
We can take advantage of this information as well with our deferral of
recursing into directories where one side matches the merge base.
Add some data structures that we will use to do these deferrals, with
some lengthy comments explaining their purpose.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The previous patch possibly raises some questions about whether
additional cases in collect_merge_info_callback() can be handled early.
Add some explanations in the form of comments to help explain these
better. While we're at it, add a few comments to denote what a few
boolean '0' or '1' values stand for.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When there are no directories involved at a given path, and all three
sides have a file at that path, and two of the three sides of history
match, we can immediately resolve the merge of that path in
collect_merge_info() and do not need to wait until process_entries().
This is actually a very minor improvement: half the time when I run it,
I see an improvement; the other half a slowdown. It seems to be in the
range of noise. However, this idea serves as the beginning of some
bigger optimizations coming in the following patches.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Code cleanup around struct_type_init() functions.
* ab/struct-init:
string-list.h users: change to use *_{nodup,dup}()
string-list.[ch]: add a string_list_init_{nodup,dup}()
dir.[ch]: replace dir_init() with DIR_INIT
*.c *_init(): define in terms of corresponding *_INIT macro
*.h: move some *_INIT to designated initializers
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The merge code had funny interactions between content based rename
detection and directory rename detection.
* en/merge-dir-rename-corner-case-fix:
merge-recursive: handle rename-to-self case
merge-ort: ensure we consult df_conflict and path_conflicts
t6423: test directory renames causing rename-to-self
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Performance tweaks of "git merge -sort" around lazy fetching of objects.
* en/ort-perf-batch-13:
merge-ort: add prefetching for content merges
diffcore-rename: use a different prefetch for basename comparisons
diffcore-rename: allow different missing_object_cb functions
t6421: add tests checking for excessive object downloads during merge
promisor-remote: output trace2 statistics for number of objects fetched
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More fix-ups and optimization to "merge -sort".
* en/ort-perf-batch-12:
merge-ort: miscellaneous touch-ups
Fix various issues found in comments
diffcore-rename: avoid unnecessary strdup'ing in break_idx
merge-ort: replace string_list_df_name_compare with faster alternative
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These were last bumped in commit 92c57e5c1d29 (bump rename limit
defaults (again), 2011-02-19), and were bumped both because processors
had gotten faster, and because people were getting ugly merges that
caused problems and reporting it to the mailing list (suggesting that
folks were willing to spend more time waiting).
Since that time:
* Linus has continued recommending kernel folks to set
diff.renameLimit=0 (maps to 32767, currently)
* Folks with repositories with lots of renames were happy to set
merge.renameLimit above 32767, once the code supported that, to
get correct cherry-picks
* Processors have gotten faster
* It has been discovered that the timing methodology used last time
probably used too large example files.
The last point is probably worth explaining a bit more:
* The "average" file size used appears to have been average blob size
in the linux kernel history at the time (probably v2.6.25 or
something close to it).
* Since bigger files are modified more frequently, such a computation
weights towards larger files.
* Larger files may be more likely to be modified over time, but are
not more likely to be renamed -- the mean and median blob size
within a tree are a bit higher than the mean and median of blob
sizes in the history leading up to that version for the linux
kernel.
* The mean blob size in v2.6.25 was half the average blob size in
history leading to that point
* The median blob size in v2.6.25 was about 40% of the mean blob size
in v2.6.25.
* Since the mean blob size is more than double the median blob size,
any file as big as the mean will not be compared to any files of
median size or less (because they'd be more than 50% dissimilar).
* Since it is the number of files compared that provides the O(n^2)
behavior, median-sized files should matter more than mean-sized
ones.
The combined effect of the above is that the file size used in past
calculations was likely about 5x too large. Combine that with a CPU
performance improvement of ~30%, and we can increase the limits by
a factor of sqrt(5/(1-.3)) = 2.67, while keeping the original stated
time limits.
Keeping the same approximate time limit probably makes sense for
diff.renameLimit (there is no progress feedback in e.g. git log -p),
but the experience above suggests merge.renameLimit could be extended
significantly. In fact, it probably would make sense to have an
unlimited default setting for merge.renameLimit, but that would
likely need to be coupled with changes to how progress is displayed.
(See https://lore.kernel.org/git/YOx+Ok%2FEYvLqRMzJ@coredump.intra.peff.net/
for details in that area.) For now, let's just bump the approximate
time limit from 10s to 1m.
(Note: We do not want to use actual time limits, because getting results
that depend on how loaded your system is that day feels bad, and because
we don't discover that we won't get all the renames until after we've
put in a lot of work rather than just upfront telling the user there are
too many files involved.)
Using the original time limit of 2s for diff.renameLimit, and bumping
merge.renameLimit from 10s to 60s, I found the following timings using
the simple script at the end of this commit message (on an AWS c5.xlarge
which reports as "Intel(R) Xeon(R) Platinum 8124M CPU @ 3.00GHz"):
N Timing
1300 1.995s
7100 59.973s
So let's round down to nice even numbers and bump the limits from
400->1000, and from 1000->7000.
Here is the measure_rename_perf script (adapted from
https://lore.kernel.org/git/20080211113516.GB6344@coredump.intra.peff.net/
in particular to avoid triggering the linear handling from
basename-guided rename detection):
#!/bin/bash
n=$1; shift
rm -rf repo
mkdir repo && cd repo
git init -q -b main
mkdata() {
mkdir $1
for i in `seq 1 $2`; do
(sed "s/^/$i /" <../sample
echo tag: $1
) >$1/$i
done
}
mkdata initial $n
git add .
git commit -q -m initial
mkdata new $n
git add .
cd new
for i in *; do git mv $i $i.renamed; done
cd ..
git rm -q -rf initial
git commit -q -m new
time git diff-tree -M -l0 --summary HEAD^ HEAD
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Elijah Newren
Junio C Hamano
Jonathan Tan
Derrick Stolee