Various subcommands of "git config" that takes value_regex
learn the "--literal-value" option to take the value_regex option
as a literal string.
* ds/config-literal-value:
config doc: value-pattern is not necessarily a regexp
config: implement --fixed-value with --get*
config: plumb --fixed-value into config API
config: add --fixed-value option, un-implemented
t1300: add test for --replace-all with value-pattern
t1300: test "set all" mode with value-pattern
config: replace 'value_regex' with 'value_pattern'
config: convert multi_replace to flags
Processes that access packdata while the .idx file gets removed
(e.g. while repacking) did not fail or fall back gracefully as they
could.
* tb/idx-midx-race-fix:
midx.c: protect against disappearing packs
packfile.c: protect against disappearing indexes
"git update-ref --stdin" learns to take multiple transactions in a
single session.
* ps/update-ref-multi-transaction:
update-ref: disallow "start" for ongoing transactions
p1400: use `git-update-ref --stdin` to test multiple transactions
update-ref: allow creation of multiple transactions
t1400: avoid touching refs on filesystem
"git add -i" failed to honor custom colors configured to show
patches, which has been corrected.
* js/add-i-color-fix:
add -i: verify in the tests that colors can be overridden
add -p: prefer color.diff.context over color.diff.plain
add -i (Perl version): color header to match the C version
add -i (built-in): use the same indentation as the Perl version
add -p (built-in): do not color the progress indicator separately
add -i (built-in): use correct names to load color.diff.* config
add -i (built-in): prevent the `reset` "color" from being configured
add -i: use `reset_color` consistently
add -p (built-in): imitate `xdl_format_hunk_hdr()` generating hunk headers
add -i (built-in): send error messages to stderr
add -i (built-in): do show an error message for incorrect inputs
If the old bitmap file contains a bitmap for a given commit, then that
commit does not need help from intermediate commits in its history to
compute its final bitmap. Eject that commit from the walk and insert it
into a separate list of reusable commits that are eventually stored in
the list of commits for computing bitmaps.
This helps the repeat bitmap computation task, even if the selected
commits shift drastically. This helps when a previously-bitmapped commit
exists in the first-parent history of a newly-selected commit. Since we
stop the walk at these commits and we use a first-parent walk, it is
harder to walk "around" these bitmapped commits. It's not impossible,
but we can greatly reduce the computation time for many selected
commits.
| runtime (sec) | peak heap (GB) |
| | |
| from | with | from | with |
| scratch | existing | scratch | existing |
-----------+---------+----------+---------+-----------
last patch | 88.478 | 53.218 | 2.157 | 2.224 |
this patch | 86.681 | 16.164 | 2.157 | 2.222 |
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous commits improved the bitmap computation process for very
long, linear histories with many refs by removing quadratic growth in
how many objects were walked. The strategy of computing "intermediate
commits" using bitmasks for which refs can reach those commits
partitioned the poset of reachable objects so each part could be walked
exactly once. This was effective for linear histories.
However, there was a (significant) drawback: wide histories with many
refs had an explosion of memory costs to compute the commit bitmasks
during the exploration that discovers these intermediate commits. Since
these wide histories are unlikely to repeat walking objects, the benefit
of walking objects multiple times was not expensive before. But now, the
commit walk *before computing bitmaps* is incredibly expensive.
In an effort to discover a happy medium, this change reduces the walk
for intermediate commits to only the first-parent history. This focuses
the walk on how the histories converge, which still has significant
reduction in repeat object walks. It is still possible to create
quadratic behavior in this version, but it is probably less likely in
realistic data shapes.
Here is some data taken on a fresh clone of the kernel:
| runtime (sec) | peak heap (GB) |
| | |
| from | with | from | with |
| scratch | existing | scratch | existing |
-----------+---------+----------+---------+-----------
original | 64.044 | 83.241 | 2.088 | 2.194 |
last patch | 45.049 | 37.624 | 2.267 | 2.334 |
this patch | 88.478 | 53.218 | 2.157 | 2.224 |
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When constructing new bitmaps, we perform a commit and tree walk in
fill_bitmap_commit() and fill_bitmap_tree(). This walk would benefit
from using existing bitmaps when available. We must track the existing
bitmaps and translate them into the new object order, but this is
generally faster than parsing trees.
In fill_bitmap_commit(), we must reorder thing somewhat. The priority
queue walks commits from newest-to-oldest, which means we correctly stop
walking when reaching a commit with a bitmap. However, if we walk trees
interleaved with the commits, then we might be parsing trees that are
actually part of a re-used bitmap. To avoid over-walking trees, add them
to a LIFO queue and walk them after exploring commits completely.
On git.git, this reduces a second immediate bitmap computation from 2.0s
to 1.0s. On linux.git, we go from 32s to 22s. On chromium's fork
network, we go from 227s to 198s.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
'find_objects()' currently needs to interact with the bitmaps khash
pretty closely. To make 'find_objects()' read a little more
straightforwardly, remove some of the khash-level details into a new
function that describes what it does: 'add_commit_to_bitmap()'.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A couple of callers within pack-bitmap.c duplicate logic to lookup a
given object id in the bitamps khash. Factor this out into a new
function, 'bitmap_for_commit()' to reduce some code duplication.
Make this new function non-static, since it will be used in later
commits from outside of pack-bitmap.c.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The on-disk bitmap format has a flag to mark a bitmap to be "reused".
This is a rather curious feature, and works like this:
- a run of pack-objects would decide to mark the last 80% of the
bitmaps it generates with the reuse flag
- the next time we generate bitmaps, we'd see those reuse flags from
the last run, and mark those commits as special:
- we'd be more likely to select those commits to get bitmaps in
the new output
- when generating the bitmap for a selected commit, we'd reuse the
old bitmap as-is (rearranging the bits to match the new pack, of
course)
However, neither of these behaviors particularly makes sense.
Just because a commit happened to be bitmapped last time does not make
it a good candidate for having a bitmap this time. In particular, we may
choose bitmaps based on how recent they are in history, or whether a ref
tip points to them, and those things will change. We're better off
re-considering fresh which commits are good candidates.
Reusing the existing bitmap _is_ a reasonable thing to do to save
computation. But only reusing exact bitmaps is a weak form of this. If
we have an old bitmap for A and now want a new bitmap for its child, we
should be able to compute that only by looking at trees and that are new
to the child. But this code would consider only exact reuse (which is
perhaps why it was eager to select those commits in the first place).
Furthermore, the recent switch to the reverse-edge algorithm for
generating bitmaps dropped this optimization entirely (and yet still
performs better).
So let's do a few cleanups:
- drop the whole "reusing bitmaps" phase of generating bitmaps. It's
not helping anything, and is mostly unused code (or worse, code that
is using CPU but not doing anything useful)
- drop the use of the on-disk reuse flag to select commits to bitmap
- stop setting the on-disk reuse flag in bitmaps we generate (since
nothing respects it anymore)
We will keep a few innards of the reuse code, which will help us
implement a more capable version of the "reuse" optimization:
- simplify rebuild_existing_bitmaps() into a function that only builds
the mapping of bits between the old and new orders, but doesn't
actually convert any bitmaps
- make rebuild_bitmap() public; we'll call it lazily to convert bitmaps
as we traverse (using the mapping created above)
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bitmap_writer_build() method calls bitmap_builder_init() to
construct a list of commits reachable from the selected commits along
with a "reverse graph". This reverse graph has edges pointing from a
commit to other commits that can reach that commit. After computing a
reachability bitmap for a commit, the values in that bitmap are then
copied to the reachability bitmaps across the edges in the reverse
graph.
We can now relax the role of the reverse graph to greatly reduce the
number of intermediate reachability bitmaps we compute during this
reverse walk. The end result is that we walk objects the same number of
times as before when constructing the reachability bitmaps, but we also
spend much less time copying bits between bitmaps and have much lower
memory pressure in the process.
The core idea is to select a set of "important" commits based on
interactions among the sets of commits reachable from each selected commit.
The first technical concept is to create a new 'commit_mask' member in the
bb_commit struct. Note that the selected commits are provided in an
ordered array. The first thing to do is to mark the ith bit in the
commit_mask for the ith selected commit. As we walk the commit-graph, we
copy the bits in a commit's commit_mask to its parents. At the end of
the walk, the ith bit in the commit_mask for a commit C stores a boolean
representing "The ith selected commit can reach C."
As we walk, we will discover non-selected commits that are important. We
will get into this later, but those important commits must also receive
bit positions, growing the width of the bitmasks as we walk. At the true
end of the walk, the ith bit means "the ith _important_ commit can reach
C."
MAXIMAL COMMITS
---------------
We use a new 'maximal' bit in the bb_commit struct to represent whether
a commit is important or not. The term "maximal" comes from the
partially-ordered set of commits in the commit-graph where C >= P if P
is a parent of C, and then extending the relationship transitively.
Instead of taking the maximal commits across the entire commit-graph, we
instead focus on selecting each commit that is maximal among commits
with the same bits on in their commit_mask. This definition is
important, so let's consider an example.
Suppose we have three selected commits A, B, and C. These are assigned
bitmasks 100, 010, and 001 to start. Each of these can be marked as
maximal immediately because they each will be the uniquely maximal
commit that contains their own bit. Keep in mind that that these commits
may have different bitmasks after the walk; for example, if B can reach
C but A cannot, then the final bitmask for C is 011. Even in these
cases, C would still be a maximal commit among all commits with the
third bit on in their masks.
Now define sets X, Y, and Z to be the sets of commits reachable from A,
B, and C, respectively. The intersections of these sets correspond to
different bitmasks:
* 100: X - (Y union Z)
* 010: Y - (X union Z)
* 001: Z - (X union Y)
* 110: (X intersect Y) - Z
* 101: (X intersect Z) - Y
* 011: (Y intersect Z) - X
* 111: X intersect Y intersect Z
This can be visualized with the following Hasse diagram:
100 010 001
| \ / \ / |
| \/ \/ |
| /\ /\ |
| / \ / \ |
110 101 011
\___ | ___/
\ | /
111
Some of these bitmasks may not be represented, depending on the topology
of the commit-graph. In fact, we are counting on it, since the number of
possible bitmasks is exponential in the number of selected commits, but
is also limited by the total number of commits. In practice, very few
bitmasks are possible because most commits converge on a common "trunk"
in the commit history.
With this three-bit example, we wish to find commits that are maximal
for each bitmask. How can we identify this as we are walking?
As we walk, we visit a commit C. Since we are walking the commits in
topo-order, we know that C is visited after all of its children are
visited. Thus, when we get C from the revision walk we inspect the
'maximal' property of its bb_data and use that to determine if C is truly
important. Its commit_mask is also nearly final. If C is not one of the
originally-selected commits, then assign a bit position to C (by
incrementing num_maximal) and set that bit on in commit_mask. See
"MULTIPLE MAXIMAL COMMITS" below for more detail on this.
Now that the commit C is known to be maximal or not, consider each
parent P of C. Compute two new values:
* c_not_p : true if and only if the commit_mask for C contains a bit
that is not contained in the commit_mask for P.
* p_not_c : true if and only if the commit_mask for P contains a bit
that is not contained in the commit_mask for P.
If c_not_p is false, then P already has all of the bits that C would
provide to its commit_mask. In this case, move on to other parents as C
has nothing to contribute to P's state that was not already provided by
other children of P.
We continue with the case that c_not_p is true. This means there are
bits in C's commit_mask to copy to P's commit_mask, so use bitmap_or()
to add those bits.
If p_not_c is also true, then set the maximal bit for P to one. This means
that if no other commit has P as a parent, then P is definitely maximal.
This is because no child had the same bitmask. It is important to think
about the maximal bit for P at this point as a temporary state: "P is
maximal based on current information."
In contrast, if p_not_c is false, then set the maximal bit for P to
zero. Further, clear all reverse_edges for P since any edges that were
previously assigned to P are no longer important. P will gain all
reverse edges based on C.
The final thing we need to do is to update the reverse edges for P.
These reverse edges respresent "which closest maximal commits
contributed bits to my commit_mask?" Since C contributed bits to P's
commit_mask in this case, C must add to the reverse edges of P.
If C is maximal, then C is a 'closest' maximal commit that contributed
bits to P. Add C to P's reverse_edges list.
Otherwise, C has a list of maximal commits that contributed bits to its
bitmask (and this list is exactly one element). Add all of these items
to P's reverse_edges list. Be careful to ignore duplicates here.
After inspecting all parents P for a commit C, we can clear the
commit_mask for C. This reduces the memory load to be limited to the
"width" of the commit graph.
Consider our ABC/XYZ example from earlier and let's inspect the state of
the commits for an interesting bitmask, say 011. Suppose that D is the
only maximal commit with this bitmask (in the first three bits). All
other commits with bitmask 011 have D as the only entry in their
reverse_edges list. D's reverse_edges list contains B and C.
COMPUTING REACHABILITY BITMAPS
------------------------------
Now that we have our definition, let's zoom out and consider what
happens with our new reverse graph when computing reachability bitmaps.
We walk the reverse graph in reverse-topo-order, so we visit commits
with largest commit_masks first. After we compute the reachability
bitmap for a commit C, we push the bits in that bitmap to each commit D
in the reverse edge list for C. Then, when we finally visit D we already
have the bits for everything reachable from maximal commits that D can
reach and we only need to walk the objects in the set-difference.
In our ABC/XYZ example, when we finally walk for the commit A we only
need to walk commits with bitmask equal to A's bitmask. If that bitmask
is 100, then we are only walking commits in X - (Y union Z) because the
bitmap already contains the bits for objects reachable from (X intersect
Y) union (X intersect Z) (i.e. the bits from the reachability bitmaps
for the maximal commits with bitmasks 110 and 101).
The behavior is intended to walk each commit (and the trees that commit
introduces) at most once while allocating and copying fewer reachability
bitmaps. There is one caveat: what happens when there are multiple
maximal commits with the same bitmask, with respect to the initial set
of selected commits?
MULTIPLE MAXIMAL COMMITS
------------------------
Earlier, we mentioned that when we discover a new maximal commit, we
assign a new bit position to that commit and set that bit position to
one for that commit. This is absolutely important for interesting
commit-graphs such as git/git and torvalds/linux. The reason is due to
the existence of "butterflies" in the commit-graph partial order.
Here is an example of four commits forming a butterfly:
I J
|\ /|
| \/ |
| /\ |
|/ \|
M N
\ /
|/
Q
Here, I and J both have parents M and N. In general, these do not need
to be exact parent relationships, but reachability relationships. The
most important part is that M and N cannot reach each other, so they are
independent in the partial order. If I had commit_mask 10 and J had
commit_mask 01, then M and N would both be assigned commit_mask 11 and
be maximal commits with the bitmask 11. Then, what happens when M and N
can both reach a commit Q? If Q is also assigned the bitmask 11, then it
is not maximal but is reachable from both M and N.
While this is not necessarily a deal-breaker for our abstract definition
of finding maximal commits according to a given bitmask, we have a few
issues that can come up in our larger picture of constructing
reachability bitmaps.
In particular, if we do not also consider Q to be a "maximal" commit,
then we will walk commits reachable from Q twice: once when computing
the reachability bitmap for M and another time when computing the
reachability bitmap for N. This becomes much worse if the topology
continues this pattern with multiple butterflies.
The solution has already been mentioned: each of M and N are assigned
their own bits to the bitmask and hence they become uniquely maximal for
their bitmasks. Finally, Q also becomes maximal and thus we do not need
to walk its commits multiple times. The final bitmasks for these commits
are as follows:
I:10 J:01
|\ /|
| \ _____/ |
| /\____ |
|/ \ |
M:111 N:1101
\ /
Q:1111
Further, Q's reverse edge list is { M, N }, while M and N both have
reverse edge list { I, J }.
PERFORMANCE MEASUREMENTS
------------------------
Now that we've spent a LOT of time on the theory of this algorithm,
let's show that this is actually worth all that effort.
To test the performance, use GIT_TRACE2_PERF=1 when running
'git repack -abd' in a repository with no existing reachability bitmaps.
This avoids any issues with keeping existing bitmaps to skew the
numbers.
Inspect the "building_bitmaps_total" region in the trace2 output to
focus on the portion of work that is affected by this change. Here are
the performance comparisons for a few repositories. The timings are for
the following versions of Git: "multi" is the timing from before any
reverse graph is constructed, where we might perform multiple
traversals. "reverse" is for the previous change where the reverse graph
has every reachable commit. Finally "maximal" is the version introduced
here where the reverse graph only contains the maximal commits.
Repository: git/git
multi: 2.628 sec
reverse: 2.344 sec
maximal: 2.047 sec
Repository: torvalds/linux
multi: 64.7 sec
reverse: 205.3 sec
maximal: 44.7 sec
So in all cases we've not only recovered any time lost to switching to
the reverse-edge algorithm, but we come out ahead of "multi" in all
cases. Likewise, peak heap has gone back to something reasonable:
Repository: torvalds/linux
multi: 2.087 GB
reverse: 3.141 GB
maximal: 2.288 GB
While I do not have access to full fork networks on GitHub, Peff has run
this algorithm on the chromium/chromium fork network and reported a
change from 3 hours to ~233 seconds. That network is particularly
beneficial for this approach because it has a long, linear history along
with many tags. The "multi" approach was obviously quadratic and the new
approach is linear.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Before 'load_bitmap_entries_v1()' reads an actual EWAH bitmap, it should
check that it can safely do so by ensuring that there are at least 6
bytes available to be read (four for the commit's index position, and
then two more for the xor offset and flags, respectively).
Likewise, it should check that the commit index it read refers to a
legitimate object in the pack.
The first fix catches a truncation bug that was exposed when testing,
and the second is purely precautionary.
There are some possible future improvements, not pursued here. They are:
- Computing the correct boundary of the bitmap itself in the caller
and ensuring that we don't read past it. This may or may not be
worth it, since in a truncation situation, all bets are off: (is the
trailer still there and the bitmap entries malformed, or is the
trailer truncated?). The best we can do is try to read what's there
as if it's correct data (and protect ourselves when it's obviously
bogus).
- Avoid the magic "6" by teaching read_be32() and read_u8() (both of
which are custom helpers for this function) to check sizes before
advancing the pointers.
- Adding more tests in this area. Testing these truncation situations
are remarkably fragile to even subtle changes in the bitmap
generation. So, the resulting tests are likely to be quite brittle.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bitmap_builder_init() method walks the reachable commits in
topological order and constructs a "reverse graph" along the way. At the
moment, this reverse graph contains an edge from commit A to commit B if
and only if A is a parent of B. Thus, the name "children" is appropriate
for for this reverse graph.
In the next change, we will repurpose the reverse graph to not be
directly-adjacent commits in the commit-graph, but instead a more
abstract relationship. The previous changes have already incorporated
the necessary updates to fill_bitmap_commit() that allow these edges to
not be immediate children.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The current rev-list tests that check the bitmap data only work on HEAD
instead of multiple branches. Expand the test cases to handle both
'master' and 'other' branches.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
It can be helpful to check if a commit_list contains a commit. Use
pointer equality, assuming lookup_commit() was used.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bitmap_is_subset() function checks if the 'self' bitmap contains any
bitmaps that are not on in the 'other' bitmap. Up until this patch, it
had a declaration, but no implementation or callers. A subsequent patch
will want this function, so implement it here.
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The current implementation of bitmap_writer_build() creates a
reachability bitmap for every walked commit. After computing a bitmap
for a commit, those bits are pushed to an in-progress bitmap for its
children.
fill_bitmap_commit() assumes the bits corresponding to objects
reachable from the parents of a commit are already set. This means that
when visiting a new commit, we only have to walk the objects reachable
between it and any of its parents.
A future change to bitmap_writer_build() will relax this condition so
not all parents have their bits set. Prepare for that by having
'fill_bitmap_commit()' walk parents until reaching commits whose bits
are already set. Then, walk the trees for these commits as well.
This has no functional change with the current implementation of
bitmap_writer_build().
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Our algorithm to generate reachability bitmaps walks through the commit
graph from the bottom up, passing bitmap data from each commit to its
descendants. For a linear stretch of history like:
A -- B -- C
our sequence of steps is:
- compute the bitmap for A by walking its trees, etc
- duplicate A's bitmap as a starting point for B; we can now free A's
bitmap, since we only needed it as an intermediate result
- OR in any extra objects that B can reach into its bitmap
- duplicate B's bitmap as a starting point for C; likewise, free B's
bitmap
- OR in objects for C, and so on...
Rather than duplicating bitmaps and immediately freeing the original, we
can just pass ownership from commit to commit. Note that this doesn't
always work:
- the recipient may be a merge which already has an intermediate
bitmap from its other ancestor. In that case we have to OR our
result into it. Note that the first ancestor to reach the merge does
get to pass ownership, though.
- we may have multiple children; we can only pass ownership to one of
them
However, it happens often enough and copying bitmaps is expensive enough
that this provides a noticeable speedup. On a clone of linux.git, this
reduces the time to generate bitmaps from 205s to 70s. This is about the
same amount of time it took to generate bitmaps using our old "many
traversals" algorithm (the previous commit measures the identical
scenario as taking 63s). It unfortunately provides only a very modest
reduction in the peak memory usage, though.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bitmap generation code works by iterating over the set of commits
for which we plan to write bitmaps, and then for each one performing a
traditional traversal over the reachable commits and trees, filling in
the bitmap. Between two traversals, we can often reuse the previous
bitmap result as long as the first commit is an ancestor of the second.
However, our worst case is that we may end up doing "n" complete
complete traversals to the root in order to create "n" bitmaps.
In a real-world case (the shared-storage repo consisting of all GitHub
forks of chromium/chromium), we perform very poorly: generating bitmaps
takes ~3 hours, whereas we can walk the whole object graph in ~3
minutes.
This commit completely rewrites the algorithm, with the goal of
accessing each object only once. It works roughly like this:
- generate a list of commits in topo-order using a single traversal
- invert the edges of the graph (so have parents point at their
children)
- make one pass in reverse topo-order, generating a bitmap for each
commit and passing the result along to child nodes
We generate correct results because each node we visit has already had
all of its ancestors added to the bitmap. And we make only two linear
passes over the commits.
We also visit each tree usually only once. When filling in a bitmap, we
don't bother to recurse into trees whose bit is already set in the
bitmap (since we know we've already done so when setting their bit).
That means that if commit A references tree T, none of its descendants
will need to open T again. I say "usually", though, because it is
possible for a given tree to be mentioned in unrelated parts of history
(e.g., cherry-picking to a parallel branch).
So we've accomplished our goal, and the resulting algorithm is pretty
simple to understand. But there are some downsides, at least with this
initial implementation:
- we no longer reuse the results of any on-disk bitmaps when
generating. So we'd expect to sometimes be slower than the original
when bitmaps already exist. However, this is something we'll be able
to add back in later.
- we use much more memory. Instead of keeping one bitmap in memory at
a time, we're passing them up through the graph. So our memory use
should scale with the graph width (times the size of a bitmap).
So how does it perform?
For a clone of linux.git, generating bitmaps from scratch with the old
algorithm took 63s. Using this algorithm it takes 205s. Which is much
worse, but _might_ be acceptable if it behaved linearly as the size
grew. It also increases peak heap usage by ~1G. That's not impossibly
large, but not encouraging.
On the complete fork-network of torvalds/linux, it increases the peak
RAM usage by 40GB. Yikes. (I forgot to record the time it took, but the
memory usage was too much to consider this reasonable anyway).
On the complete fork-network of chromium/chromium, I ran out of memory
before succeeding. Some back-of-the-envelope calculations indicate it
would need 80+GB to complete.
So at this stage, we've managed to make things much worse. But because
of the way this new algorithm is structured, there are a lot of
opportunities for optimization on top. We'll start implementing those in
the follow-on patches.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There's no easy way to make a copy of a bitmap. Obviously a caller can
iterate over the bits and set them one by one in a new bitmap, but we
can go much faster by copying whole words with memcpy().
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We have a function to bitwise-OR an ewah into an uncompressed bitmap,
but not to OR two uncompressed bitmaps. Let's add it.
Interestingly, we have a public header declaration going back to
e1273106f6 (ewah: compressed bitmap implementation, 2013-11-14), but the
function was never implemented. That was all OK since there were no
users of 'bitmap_or()', but a first caller will be added in a couple of
patches.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If you ask to set a bit in the Nth word and we haven't yet allocated
that many slots in our array, we'll increase the bitmap size to 2*N.
This means we might frequently end up with bitmaps that are twice the
necessary size (as soon as you ask for the biggest bit, we'll size up to
twice that).
But if we just allocate as many words as were asked for, we may not grow
fast enough. The worst case there is setting bit 0, then 1, etc. Each
time we grow we'd just extend by one more word, giving us linear
reallocations (and quadratic memory copies).
A middle ground is relying on alloc_nr(), which causes us to grow by a
factor of roughly 3/2 instead of 2. That's less aggressive than
doubling, and it may help avoid fragmenting memory. (If we start with N,
then grow twice, our total is N*(3/2)^2 = 9N/4. After growing twice,
that array of size 9N/4 can fit into the space vacated by the original
array and first growth, N+3N/2 = 10N/4 > 9N/4, leading to less
fragmentation in memory).
Our worst case is still 3/2N wasted bits (you set bit N-1, then setting
bit N causes us to grow by 3/2), but our average should be much better.
This isn't usually that big a deal, but it will matter as we shift the
reachability bitmap generation code to store more bitmaps in memory.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We auto-grow bitmaps when somebody asks to set a bit whose position is
outside of our currently allocated range. Other operations besides
single bit-setting might need to do this, too, so let's pull it into its
own function.
Note that we change the semantics a little: you now ask for the number
of words you'd like to have, not the id of the block you'd like to write
to.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
You can use "git rev-list --test-bitmap HEAD" to check that bitmaps
produce the same answer we'd get from a regular traversal. But if we
detect an error, we only print "mismatch", and still exit with a
successful error code.
That makes the uses of --test-bitmap in the test suite (e.g., in t5310)
mostly pointless: even if we saw an error, the tests wouldn't notice.
Let's instead call die(), which will let these tests work as designed,
and alert us if the bitmaps are bogus.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We truncate the .bitmap file to 512 bytes and expect to run into
problems reading an individual ewah file. But this length is somewhat
arbitrary, and just happened to work when the test was added in
9d2e330b17 (ewah_read_mmap: bounds-check mmap reads, 2018-06-14).
An upcoming commit will change the size of the history we create in the
test repo, which will cause this test to fail. We can future-proof it a
bit more by reducing the size of the truncated bitmap file.
Signed-off-by: Jeff King <peff@peff.net>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A .bitmap file may have a "name hash cache" extension, which puts a
sequence of uint32_t values (one per object) at the end of the file.
When we see a flag indicating this extension, we blindly subtract the
appropriate number of bytes from our available length. However, if the
.bitmap file is too short, we'll underflow our length variable and wrap
around, thinking we have a very large length. This can lead to reading
out-of-bounds bytes while loading individual ewah bitmaps.
We can fix this by checking the number of available bytes when we parse
the header. The existing "truncated bitmap" test is now split into two
tests: one where we don't have this extension at all (and hence actually
do try to read a truncated ewah bitmap) and one where we realize
up-front that we can't even fit in the cache structure. We'll check
stderr in each case to make sure we hit the error we're expecting.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we parse a .bitmap header, we first check that we have enough bytes
to make a valid header. We do that based on sizeof(struct
bitmap_disk_header). However, as of 0f4d6cada8 (pack-bitmap: make bitmap
header handling hash agnostic, 2019-02-19), that struct oversizes its
checksum member to GIT_MAX_RAWSZ. That means we need to adjust for the
difference between that constant and the size of the actual hash we're
using. That commit adjusted the code which moves our pointer forward,
but forgot to update the size check.
This meant we were overly strict about the header size (requiring room
for a 32-byte worst-case hash, when sha1 is only 20 bytes). But in
practice it didn't matter because bitmap files tend to have at least 12
bytes of actual data anyway, so it was unlikely for a valid file to be
caught by this.
Let's fix it by pulling the header size into a separate variable and
using it in both spots. That fixes the bug and simplifies the code to make
it harder to have a mismatch like this in the future. It will also come
in handy in the next patch for more bounds checking.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
'ewah/ewah_bitmap.c:buffer_grow()' is responsible for growing the buffer
used to store the bits of an EWAH bitmap. It is essentially doing the
same task as the 'ALLOC_GROW()' macro, so use that instead.
This simplifies the callers of 'buffer_grow()', who no longer have to
ask for a specific size, but rather specify how much of the buffer they
need. They also no longer need to guard 'buffer_grow()' behind an if
statement, since 'ALLOC_GROW()' (and, by extension, 'buffer_grow()') is
a noop if the buffer is already large enough.
But, the most significant change is that this fixes a bug when calling
buffer_grow() with both 'alloc_size' and 'new_size' set to 1. In this
case, truncating integer math will leave the new size set to 1, causing
the buffer to never grow.
Instead, let alloc_nr() handle this, which asks for '(new_size + 16) * 3
/ 2' instead of 'new_size * 3 / 2'.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To allow us to consider a change in the default behavior of `git init`
where it uses a more inclusive name for the initial branch, we must
first teach the test suite not to rely on a specific default branch
name. In this patch, we teach t7064 that trick.
To that end, we set a specific name for the initial branch. Ideally, we
would simply start out by calling `git branch -M initial-branch`, but
there is a bug in `git branch -M` that does not allow renaming branches
unless they already have commits. This will be fixed in the
`js/init-defaultbranch-advice` topic, and until that time, we use the
equivalent (but less intuitive) `git checkout -f --orphan`.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Long time ago when the _git_complete helper was introduced, _gitk was
replaced with __gitk_main, and a placeholder for backwards compatibility
pointing to __git_wrap_main_gitk was left in place.
When "__git_complete gitk __gitk_main" was called, that created the
__git_wrap__gitk_main helper, which is just basically "__git_func_wrap
__gitk_main" plus `complete` options.
Unfortunately the commit b0a4b2d257 (completion: add support for
backwards compatibility, 2012-05-19) missed a previous instance of a
call to _gitk in _git_gitk
So, basically we had __git_wrap__git_main -> __git_func_wrap __git_main ->
__git_complete_command gitk -> _git_gitk -> _gitk ->
__git_wrap__gitk_main -> __git_func_wrap __gitk_main -> __gitk_main.
There was never any need to call __git_func_wrap twice. Since _git_gitk
is always called inside the wrapper, it can call __gitk_main directly.
And then, in commit 441ecdab37 (completion: bash: remove old compat
wrappers, 2020-10-27) _gitk was removed, which triggers the following
error:
_git_gitk:9: command not found: _gitk
Let's call the correct function: __gitk_main.
Cc: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Our packed_commit_list is an array of pointers to commit structs. We use
"int" for the allocation, which is 32-bit even on 64-bit platforms. This
isn't likely to overflow in practice (we're writing commit graphs, so
you'd need to actually have billions of unique commits in the
repository). But it's good practice to use size_t for allocations.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Our custom packed_oid_list data structure is really just an oid_array in
disguise. Let's switch to using the generic structure, which shortens
and simplifies the code slightly.
There's one slightly awkward part: in the old code we copied a hash
straight from the mmap'd on-disk data into the final object_id. And now
we'll copy to a temporary oid, which we'll then pass to
oid_array_append(). But this is an operation we have to do all over the
commit-graph code already, since it mostly uses object_id structs
internally. I also measured "git commit-graph --append", which triggers
this code path, and it showed no difference.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When writing a commit graph, we collect a list of object ids in an
array, which we'll eventually copy into an array of "struct commit"
pointers. Before we do that, though, we count the number of distinct
commit entries. There's a subtle bug in this step, though.
We eliminate not only duplicate oids, but also in split mode, any oids
which are not commits or which are already in a graph file. However, the
loop starts at index 1, always counting index 0 as distinct. And indeed
it can't be a duplicate, since we check for those by comparing against
the previous entry, and there isn't one for index 0. But it could be a
commit that's already in a graph file, and we'd overcount the number of
commits by 1 in that case.
That turns out not to be a problem, though. The only things we do with
the count are:
- check if our count will overflow our data structures. But the limit
there is 2^31 commits, so while this is a useful check, the
off-by-one is not likely to matter.
- pre-allocate the array of commit pointers. But over-allocating by
one isn't a problem; we'll just waste a few extra bytes.
The bug would be easy enough to fix, but we can observe that neither of
those steps is necessary.
After building the actual commit array, we'll likewise check its count
for overflow. So the extra check of the distinct commit count here is
redundant.
And likewise we use ALLOC_GROW() when building the commit array, so
there's no need to preallocate it (it's possible that doing so is
slightly more efficient, but if we care we can just optimistically
allocate one slot for each oid; I didn't bother here).
So count_distinct_commits() isn't doing anything useful. Let's just get
rid of that step.
Note that a side effect of the function was that we sorted the list of
oids, which we do rely on in copy_oids_to_commits(), since it must also
skip the duplicates. So we'll move the qsort there. I didn't copy the
"TODO" about adding more progress meters. It's actually quite hard to
make a repository large enough for this qsort would take an appreciable
amount of time, so this doesn't seem like a useful note.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We provide oid_array_for_each_unique() for iterating over the
de-duplicated items in an array. But it's awkward to use for two
reasons:
1. It uses a callback, which means marshaling arguments into a struct
and passing it to the callback with a void parameter.
2. The callback doesn't know the numeric index of the oid we're
looking at. This is useful for things like progress meters.
Iterating with a for-loop is much more natural for some cases, but the
caller has to do the de-duping itself. However, we can provide a small
helper to make this easier (see the docstring in the header for an
example use).
The caller does have to remember to sort the array first. We could add
an assertion into the helper that array->sorted is set, but I didn't
want to complicate what is otherwise a pretty fast code path.
I also considered adding a full iterator type with init/next/end
functions (similar to what we have for hashmaps). But it ended up making
the callers much harder to read. This version keeps us close to a basic
for-loop.
Yet another option would be adding an option to sort the array and
compact out the duplicates. This would mean iterating over the array an
extra time, though that's probably not a big deal (we did just do an
O(n log n) sort). But we'd still have to write a for-loop to iterate, so
it doesn't really make anything easier for the caller.
No new test, since we'll convert the callback iterator (which is covered
by t0064, among other callers) to use the new code.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Our test suite currently only passes when `git init` uses the name
`master` for the initial branch. This would stop us from changing the
default branch name.
Let's adjust t6300 so that it does not rely on any specific default
branch name. This trick is done by (force-)renaming the initial branch
to the name `main` in the `setup` and the `:remotename and :remoteref`
test cases, and then replacing all mentions of `master` and `MASTER`
with `main` and `MAIN`, respectively.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Split a very long line in a test introduced in 0b691d8685 (pretty:
add support for separator option in %(trailers), 2019-01-28). This
makes it easier to read, especially as follow-up commits will copy
this test as a template.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We sort the oid-array as a side effect of calling the lookup or
unique-iteration functions. But callers may want to sort it themselves
(especially as we add new iteration options in future patches).
We'll also move the check of the "sorted" flag into the sort function,
so callers don't have to remember to check it.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We define git_hash_algo and object_id in hash.h, but most of the utility
functions are declared in the main cache.h. Let's move them to hash.h
along with their struct definitions. This cleans up cache.h a bit, but
also avoids circular dependencies when other headers need to know about
these functions (e.g., if oid-array.h were to have an inline that used
oideq(), it couldn't include cache.h because it is itself included by
cache.h).
No including C files should be affected, because hash.h is always
included in cache.h already.
We do have to mention repository.h at the top of hash.h, though, since
we depend on the_repository in some of our inline functions.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Our tests for handling duplicates in oid-array provide only a single
duplicate for each number, so our sorted array looks like:
44 44 55 55 88 88 aa aa
A slightly more interesting test is to have multiple duplicates, which
makes sure that we not only skip the duplicate, but keep skipping until
we are out of the set of matching duplicates.
Unsurprisingly this works just fine, but it's worth beefing up this test
since we're about to change the duplicate-detection code.
Note that we do need to adjust the results on the lookup test, since it
is returning the index of the found item (and now we have more items
before our range, and the range itself is slightly larger, since we'll
accept a match of any element).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The data type is an oid_array these days, and we are using "test-tool
oid-array", so let's name the test script appropriately.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When this file was moved from sha1-array.h, we forgot to update the
preprocessor header guard to match the new name.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 0a21d0e089 (Makefile: mark git-maintenance as a builtin,
2020-12-01), we marked git-maintenance as a builtin in the Makefile, but
forgot to do the same in `CMakeLists.txt`.
Rather than always play catch-up and adjust `git_builtin_extra`
manually, use the `BUILT_INS` definitions in the Makefile as
authoritative source and generate `git_builtin_extra` dynamically.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Initially, we started converting this test script in anticipation for
renaming the default branch name to `main`. To that end, we partially
converted it to accommodate for that default branch name, marking the
now-failing test cases with a prereq that was designed to be fulfilled
once the rename was complete.
However, the effort to move to the branch name `main` needs quite a bit
longer, as it was decided that we need a deprecation phase first.
To avoid keeping t5526 in limbo for such a long time, we just made it
independent of the actual default branch name used by Git. Therefore,
that prereq is no longer necessary, and we can drop it.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
While at it, use different default branch names for the three different
repositories involved in the test script: this makes it easier to debug
failures, too (otherwise you have to wonder which `master` branch was
meant: the super project's? The submodule's? The nested submodule's?).
Note: this touches code that was originally modified to prepare for
renaming the default branch name to `main`. This patch side-steps that
effort completely by overriding the initial branch name explicitly.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Something changed in `vcpkg` (which we use in our Visual C++ build to
provide the dependencies such as libcurl) and our `vs-build` job started
failing in CI. The reason is that we had a work-around in place to help
CMake find iconv, and this work-around is neither needed nor does it
work anymore.
For the full discussion with the vcpkg project, see this comment:
https://github.com/microsoft/vcpkg/issues/14780#issuecomment-735368280
Signed-off-by: Dennis Ameling <dennis@dennisameling.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To keep track of which object filters are allowed or not, 'git
upload-pack' stores the name of each filter in a string_list, and sets
it ->util pointer to be either 0 or 1, indicating whether it is banned
or allowed.
Later on, we attempt to clear that list, but we incorrectly ask for the
util pointers to be free()'d, too. This behavior (introduced back in
6dd3456a8c (upload-pack.c: allow banning certain object filter(s),
2020-08-03)) leads to an invalid free, and causes us to crash.
In order to trigger this, one needs to fetch from a server that (a) has
at least one object filter allowed, and (b) issue a fetch that contains
a subset of the allowed filters (i.e., we cannot ask for a banned
filter, since this causes us to die() before we hit the bogus
string_list_clear()).
In that case, whatever banned filters exist will cause a noop free()
(since those ->util pointers are set to 0), but the first allowed filter
we try to free will crash us.
We never noticed this in the tests because we didn't have an example of
setting 'uploadPackFilter' configuration variables and then following up
with a valid fetch. The first new 'git clone' prevents further
regression here. For good measure on top, add a test which checks the
same behavior at a tree depth greater than 0.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If 'git clone' couldn't execute 'transport_fetch_refs()' (e.g., because
of an error on the remote's side in 'git upload-pack'), then it will
silently ignore it.
Even though this has been the case at least since clone was ported to C
(way back in 8434c2f1af (Build in clone, 2008-04-27)), 'git fetch'
doesn't ignore these and reports any failures it sees.
That suggests that ignoring the return value in 'git clone' is simply an
oversight that should be corrected. That's exactly what this patch does.
(Noticing and fixing this is no coincidence, we'll want it in the next
patch in order to demonstrate a regression in 'git upload-pack' via a
'git clone'.)
There's no additional logging here, but that matches how 'git fetch'
handles the same case. An assumption there is that whichever part of
transport_fetch_refs() fails will complain loudly, so any additional
logging here is redundant.
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
