Annotate function parameters that are not used (but cannot be
removed for structural reasons), to prepare us to later compile
with -Wunused warning turned on.
* jk/unused-annotation:
is_path_owned_by_current_uid(): mark "report" parameter as unused
run-command: mark unused async callback parameters
mark unused read_tree_recursive() callback parameters
hashmap: mark unused callback parameters
config: mark unused callback parameters
streaming: mark unused virtual method parameters
transport: mark bundle transport_options as unused
refs: mark unused virtual method parameters
refs: mark unused reflog callback parameters
refs: mark unused each_ref_fn parameters
git-compat-util: add UNUSED macro
An earlier optimization discarded a tree-object buffer that is
still in use, which has been corrected.
* jk/is-promisor-object-keep-tree-in-use:
is_promisor_object(): fix use-after-free of tree buffer
Hashmap comparison functions must conform to a particular callback
interface, but many don't use all of their parameters. Especially the
void cmp_data pointer, but some do not use keydata either (because they
can easily form a full struct to pass when doing lookups). Let's mark
these to make -Wunused-parameter happy.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git fsck" reads mode from tree objects but canonicalizes the mode
before passing it to the logic to check object sanity, which has
hid broken tree objects from the checking logic. This has been
corrected, but to help exiting projects with broken tree objects
that they cannot fix retroactively, the severity of anomalies this
code detects has been demoted to "info" for now.
* jk/fsck-tree-mode-bits-fix:
fsck: downgrade tree badFilemode to "info"
fsck: actually detect bad file modes in trees
tree-walk: add a mechanism for getting non-canonicalized modes
Since commit fcc07e980b (is_promisor_object(): free tree buffer after
parsing, 2021-04-13), we'll always free the buffers attached to a
"struct tree" after searching them for promisor links. But there's an
important case where we don't want to do so: if somebody else is already
using the tree!
This can happen during a "rev-list --missing=allow-promisor" traversal
in a partial clone that is missing one or more trees or blobs. The
backtrace for the free looks like this:
#1 free_tree_buffer tree.c:147
#2 add_promisor_object packfile.c:2250
#3 for_each_object_in_pack packfile.c:2190
#4 for_each_packed_object packfile.c:2215
#5 is_promisor_object packfile.c:2272
#6 finish_object__ma builtin/rev-list.c:245
#7 finish_object builtin/rev-list.c:261
#8 show_object builtin/rev-list.c:274
#9 process_blob list-objects.c:63
#10 process_tree_contents list-objects.c:145
#11 process_tree list-objects.c:201
#12 traverse_trees_and_blobs list-objects.c:344
[...]
We're in the middle of walking through the entries of a tree object via
process_tree_contents(). We see a blob (or it could even be another tree
entry) that we don't have, so we call is_promisor_object() to check it.
That function loops over all of the objects in the promisor packfile,
including the tree we're currently walking. When we're done with it
there, we free the tree buffer. But as we return to the walk in
process_tree_contents(), it's still holding on to a pointer to that
buffer, via its tree_desc iterator, and it accesses the freed memory.
Even a trivial use of "--missing=allow-promisor" triggers this problem,
as the included test demonstrates (it's just a vanilla --blob:none
clone).
We can detect this case by only freeing the tree buffer if it was
allocated on our behalf. This is a little tricky since that happens
inside parse_object(), and it doesn't tell us whether the object was
already parsed, or whether it allocated the buffer itself. But by
checking for an already-parsed tree beforehand, we can distinguish the
two cases.
That feels a little hacky, and does incur an extra lookup in the
object-hash table. But that cost is fairly minimal compared to actually
loading objects (and since we're iterating the whole pack here, we're
likely to be loading most objects, rather than reusing cached results).
It may also be a good direction for this function in general, as there
are other possible optimizations that rely on doing some analysis before
parsing:
- we could detect blobs and avoid reading their contents; they can't
link to other objects, but parse_object() doesn't know that we don't
care about checking their hashes.
- we could avoid allocating object structs entirely for most objects
(since we really only need them in the oidset), which would save
some memory.
- promisor commits could use the commit-graph rather than loading the
object from disk
This commit doesn't do any of those optimizations, but I think it argues
that this direction is reasonable, rather than relying on parse_object()
and trying to teach it to give us more information about whether it
parsed.
The included test fails reliably under SANITIZE=address just when
running "rev-list --missing=allow-promisor". Checking the output isn't
strictly necessary to detect the bug, but it seems like a reasonable
addition given the general lack of coverage for "allow-promisor" in the
test suite.
Reported-by: Andrew Olsen <andrew.olsen@koordinates.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When using init_tree_desc() and tree_entry() to iterate over a tree, we
always canonicalize the modes coming out of the tree. This is a good
thing to prevent bugs or oddities in normal code paths, but it's
counter-productive for tools like fsck that want to see the exact
contents.
We can address this by adding an option to avoid the extra
canonicalization. A few notes on the implementation:
- I've attached the new option to the tree_desc struct itself. The
actual code change is in decode_tree_entry(), which is in turn
called by the public update_tree_entry(), tree_entry(), and
init_tree_desc() functions, plus their "gently" counterparts.
By letting it ride along in the struct, we can avoid changing the
signature of those functions, which are called many times. Plus it's
conceptually simpler: you really want a particular iteration of a
tree to be "raw" or not, rather than individual calls.
- We still have to set the new option somewhere. The struct is
initialized by init_tree_desc(). I added the new flags field only to
the "gently" version. That avoids disturbing the much more numerous
non-gentle callers, and it makes sense that anybody being careful
about looking at raw modes would also be careful about bogus trees
(i.e., the caller will be something like fsck in the first place).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Make our mergesort implementation type-safe.
* rs/mergesort:
mergesort: remove llist_mergesort()
packfile: use DEFINE_LIST_SORT
fetch-pack: use DEFINE_LIST_SORT
commit: use DEFINE_LIST_SORT
blame: use DEFINE_LIST_SORT
test-mergesort: use DEFINE_LIST_SORT
test-mergesort: use DEFINE_LIST_SORT_DEBUG
mergesort: add macros for typed sort of linked lists
mergesort: tighten merge loop
mergesort: unify ranks loops
Build a typed sort function for packed_git lists using DEFINE_LIST_SORT
instead of calling llist_mergesort(). This gets rid of the next pointer
accessor functions and their calling overhead at the cost of slightly
increased object text size.
Before:
__TEXT __DATA __OBJC others dec hex
20218 320 0 110936 131474 20192 packfile.o
With this patch:
__TEXT __DATA __OBJC others dec hex
20430 320 0 112619 133369 208f9 packfile.o
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Collection of what is referenced by objects in promisor packs have
been optimized to inspect these objects in the in-pack order.
* jk/optim-promisor-object-enumeration:
is_promisor_object(): walk promisor packs in pack-order
When we generate the list of promisor objects, we walk every pack with a
.promisor file and examine its objects for any links to other objects.
By default, for_each_packed_object() will go in pack .idx order.
This is the worst case with respect to our delta base cache. If we have
a delta chain of A->B->C->D, then visiting A may require reconstructing
both B and C, unless we also visited B recently, in which case we may
have cached its value. Because .idx order is based on sha1, it's random
with respect to the actual object contents and deltas, and thus we're
unlikely to get many cache hits.
If we instead traverse in pack order, then we get the optimal case:
packs are written to keep delta families together, and to place bases
before their children.
Even on a modest repository like git.git, this has a noticeable speedup
on p5600.4, which runs "fsck" on a partial clone with blob:none (so lots
of trees which need to be walked, and which delta well):
Test HEAD^ HEAD
-------------------------------------------------------
5600.4: 17.87(17.83+0.04) 15.42(15.35+0.06) -13.7%
On a larger repository like linux.git, the speedup is even more
pronounced:
Test HEAD^ HEAD
-----------------------------------------------------------
5600.4: 322.47(322.01+0.42) 186.41(185.76+0.63) -42.2%
Any other operations that call is_promisor_object(), like "rev-list
--exclude-promisor-objects", would similarly benefit, but the
invocations in p5600 don't actually trigger any such cases.
Note that we may pay a small price to build a rev-index in-memory to do
the pack-order traversal. But it's still a big net win, and even that
small cost goes away if you are using pack.writeReverseIndex.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A mechanism to pack unreachable objects into a "cruft pack",
instead of ejecting them into loose form to be reclaimed later, has
been introduced.
* tb/cruft-packs:
sha1-file.c: don't freshen cruft packs
builtin/gc.c: conditionally avoid pruning objects via loose
builtin/repack.c: add cruft packs to MIDX during geometric repack
builtin/repack.c: use named flags for existing_packs
builtin/repack.c: allow configuring cruft pack generation
builtin/repack.c: support generating a cruft pack
builtin/pack-objects.c: --cruft with expiration
reachable: report precise timestamps from objects in cruft packs
reachable: add options to add_unseen_recent_objects_to_traversal
builtin/pack-objects.c: --cruft without expiration
builtin/pack-objects.c: return from create_object_entry()
t/helper: add 'pack-mtimes' test-tool
pack-mtimes: support writing pack .mtimes files
chunk-format.h: extract oid_version()
pack-write: pass 'struct packing_data' to 'stage_tmp_packfiles'
pack-mtimes: support reading .mtimes files
Documentation/technical: add cruft-packs.txt
To store the individual mtimes of objects in a cruft pack, introduce a
new `.mtimes` format that can optionally accompany a single pack in the
repository.
The format is defined in Documentation/technical/pack-format.txt, and
stores a 4-byte network order timestamp for each object in name (index)
order.
This patch prepares for cruft packs by defining the `.mtimes` format,
and introducing a basic API that callers can use to read out individual
mtimes.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
shift count being exactly at 7-bit smaller than the long is OK; on
32-bit architecture, shift count starts at 4 and goes through 11, 18
and 25, at which point the guard triggers one iteration too early.
Reported-by: Marc Strapetz <marc.strapetz@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The code to decode the length of packed object size has been
corrected.
* jt/pack-header-lshift-overflow:
packfile: avoid overflowing shift during decode
Since its definition in 2f4ba2a867 (packfile: prepare for the existence
of '*.rev' files, 2021-01-25), the only caller of
`close_pack_revindex()` was within packfile.c.
Thus there is no need for this to be exposed via packfile.h, and instead
can remain static within packfile.c's compilation unit. While we're
here, move the function's opening brace onto its own line.
Noticed-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The clean/smudge conversion code path has been prepared to better
work on platforms where ulong is narrower than size_t.
* mc/clean-smudge-with-llp64:
clean/smudge: allow clean filters to process extremely large files
odb: guard against data loss checking out a huge file
git-compat-util: introduce more size_t helpers
odb: teach read_blob_entry to use size_t
t1051: introduce a smudge filter test for extremely large files
test-lib: add prerequisite for 64-bit platforms
test-tool genzeros: generate large amounts of data more efficiently
test-genzeros: allow more than 2G zeros in Windows
unpack_object_header_buffer() attempts to protect against overflowing
left shifts, but the limit of the shift amount should not be the size of
the variable being shifted. It should be the size minus the size of its
contents. Fix that accordingly.
This was noticed at $DAYJOB by a fuzzer running internally.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This introduces an additional guard for platforms where `unsigned long`
and `size_t` are not of the same size. If the size of an object in the
database would overflow `unsigned long`, instead we now exit with an
error.
A complete fix will have to update _many_ other functions throughout the
codebase to use `size_t` instead of `unsigned long`. It will have to be
implemented at some stage.
This commit puts in a stop-gap for the time being.
Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Matt Cooper <vtbassmatt@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Unusable entries of a damaged pack file are recorded in the oidset
bad_objects. Release it when we're done with the pack.
This doesn't affect intact packs because an empty oidset requires
no allocation.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Replace a handcrafted data structure used to keep track of bad
objects in the packfile API by an oidset.
* rs/packfile-bad-object-list-in-oidset:
packfile: use oidset for bad objects
packfile: convert has_packed_and_bad() to object_id
packfile: convert mark_bad_packed_object() to object_id
midx: inline nth_midxed_pack_entry()
oidset: make oidset_size() an inline function
The reachability bitmap file used to be generated only for a single
pack, but now we've learned to generate bitmaps for history that
span across multiple packfiles.
* tb/multi-pack-bitmaps: (29 commits)
pack-bitmap: drop bitmap_index argument from try_partial_reuse()
pack-bitmap: drop repository argument from prepare_midx_bitmap_git()
p5326: perf tests for MIDX bitmaps
p5310: extract full and partial bitmap tests
midx: respect 'GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP'
t7700: update to work with MIDX bitmap test knob
t5319: don't write MIDX bitmaps in t5319
t5310: disable GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP
t0410: disable GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP
t5326: test multi-pack bitmap behavior
t/helper/test-read-midx.c: add --checksum mode
t5310: move some tests to lib-bitmap.sh
pack-bitmap: write multi-pack bitmaps
pack-bitmap: read multi-pack bitmaps
pack-bitmap.c: avoid redundant calls to try_partial_reuse
pack-bitmap.c: introduce 'bitmap_is_preferred_refname()'
pack-bitmap.c: introduce 'nth_bitmap_object_oid()'
pack-bitmap.c: introduce 'bitmap_num_objects()'
midx: avoid opening multiple MIDXs when writing
midx: close linked MIDXs, avoid leaking memory
...
Store the object ID of broken pack entries in an oidset instead of
keeping only their hashes in an unsorted array. The resulting code is
shorter and easier to read. It also handles the (hopefully) very rare
case of having a high number of bad objects better.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The single caller has a full object ID, so pass it on instead of just
its hash member.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
All callers have full object IDs, so pass them on instead of just their
hash member.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This prepares the code in pack-bitmap to interpret the new multi-pack
bitmaps described in Documentation/technical/bitmap-format.txt, which
mostly involves converting bit positions to accommodate looking them up
in a MIDX.
Note that there are currently no writers who write multi-pack bitmaps,
and that this will be implemented in the subsequent commit. Note also
that get_midx_checksum() and get_midx_filename() are made non-static so
they can be called from pack-bitmap.c.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The next patch will reimplement a function that wants to iterate over
packed objects while ignoring packs which are marked as kept (either
in-core or on-disk).
Teach for_each_packed_object() to ignore all objects from those packs by
adding a new flag for each of the "kept" states that a pack can be in.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Linux users may benefit from additional information on how to
avoid ENOMEM from mmap despite the system having enough RAM to
accomodate them. We can't reliably unmap pack windows to work
around the issue since malloc and other library routines may
mmap without our knowledge.
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git clean" and "git ls-files -i" had confusion around working on
or showing ignored paths inside an ignored directory, which has
been corrected.
* en/dir-traversal:
dir: introduce readdir_skip_dot_and_dotdot() helper
dir: update stale description of treat_directory()
dir: traverse into untracked directories if they may have ignored subfiles
dir: avoid unnecessary traversal into ignored directory
t3001, t7300: add testcase showcasing missed directory traversal
t7300: add testcase showing unnecessary traversal into ignored directory
ls-files: error out on -i unless -o or -c are specified
dir: report number of visited directories and paths with trace2
dir: convert trace calls to trace2 equivalents
Many places in the code were doing
while ((d = readdir(dir)) != NULL) {
if (is_dot_or_dotdot(d->d_name))
continue;
...process d...
}
Introduce a readdir_skip_dot_and_dotdot() helper to make that a one-liner:
while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
...process d...
}
This helper particularly simplifies checks for empty directories.
Also use this helper in read_cached_dir() so that our statistics are
consistent across platforms. (In other words, read_cached_dir() should
have been using is_dot_or_dotdot() and skipping such entries, but did
not and left it to treat_path() to detect and mark such entries as
path_none.)
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To get the list of all promisor objects, we not only include all objects
in promisor packs, but also parse each of those objects to see which
objects they reference. After parsing a tree object, the tree->buffer
field will remain populated until we explicitly free it. So in a partial
clone of blob:none, for example, we are essentially reading every tree
in the repository (since they're all in the initial promisor pack), and
keeping all of their uncompressed contents in memory at once.
This patch frees the tree buffers after we've finished marking all of
their reachable objects. We shouldn't need to do this for any other
object type. While we are using some extra memory to store the structs,
no other object type stores the whole contents in its parsed form (we do
sometimes hold on to commit buffers, but less so these days due to
commit graphs, plus most commands which care about promisor objects turn
off the save_commit_buffer global).
Even for a moderate-sized repository like git.git, this patch drops the
peak heap (as measured by massif) for git-fsck from ~1.7GB to ~138MB.
Fsck is a good candidate for measuring here because it doesn't interact
with the promisor code except to call is_promisor_object(), so we can
isolate just this problem.
The added perf test shows only a tiny improvement on my machine for
git.git, since 1.7GB isn't enough to cause any real memory pressure:
Test HEAD^ HEAD
--------------------------------------------------------------------------------
5600.4: fsck 21.26(20.90+0.35) 20.84(20.79+0.04) -2.0%
With linux.git the absolute change is a bit bigger, though still a small
percentage:
Test HEAD^ HEAD
-----------------------------------------------------------------------------
5600.4: fsck 262.26(259.13+3.12) 254.92(254.62+0.29) -2.8%
I didn't have the patience to run it under massif with linux.git, but
it's probably on the order of about 14GB improvement, since that's the
sum of the sizes of all of the uncompressed trees (but still isn't
enough to create memory pressure on this particular machine, which has
64GB of RAM). Smaller machines would probably see a bigger effect on
runtime (and sadly our perf suite does not measure peak heap).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
An on-disk reverse-index to map the in-pack location of an object
back to its object name across multiple packfiles is introduced.
* tb/reverse-midx:
midx.c: improve cache locality in midx_pack_order_cmp()
pack-revindex: write multi-pack reverse indexes
pack-write.c: extract 'write_rev_file_order'
pack-revindex: read multi-pack reverse indexes
Documentation/technical: describe multi-pack reverse indexes
midx: make some functions non-static
midx: keep track of the checksum
midx: don't free midx_name early
midx: allow marking a pack as preferred
t/helper/test-read-midx.c: add '--show-objects'
builtin/multi-pack-index.c: display usage on unrecognized command
builtin/multi-pack-index.c: don't enter bogus cmd_mode
builtin/multi-pack-index.c: split sub-commands
builtin/multi-pack-index.c: define common usage with a macro
builtin/multi-pack-index.c: don't handle 'progress' separately
builtin/multi-pack-index.c: inline 'flags' with options
Implement reading for multi-pack reverse indexes, as described in the
previous patch.
Note that these functions don't yet have any callers, and won't until
multi-pack reachability bitmaps are introduced in a later patch series.
In the meantime, this patch implements some of the infrastructure
necessary to support multi-pack bitmaps.
There are three new functions exposed by the revindex API:
- load_midx_revindex(): loads the reverse index corresponding to the
given multi-pack index.
- midx_to_pack_pos() and pack_pos_to_midx(): these convert between the
multi-pack index and pseudo-pack order.
load_midx_revindex() and pack_pos_to_midx() are both relatively
straightforward.
load_midx_revindex() needs a few functions to be exposed from the midx
API. One to get the checksum of a midx, and another to get the .rev's
filename. Similar to recent changes in the packed_git struct, three new
fields are added to the multi_pack_index struct: one to keep track of
the size, one to keep track of the mmap'd pointer, and another to point
past the header and at the reverse index's data.
pack_pos_to_midx() simply reads the corresponding entry out of the
table.
midx_to_pack_pos() is the trickiest, since it needs to find an object's
position in the psuedo-pack order, but that order can only be recovered
in the .rev file itself. This mapping can be implemented with a binary
search, but note that the thing we're binary searching over isn't an
array of values, but rather a permuted order of those values.
So, when comparing two items, it's helpful to keep in mind the
difference. Instead of a traditional binary search, where you are
comparing two things directly, here we're comparing a (pack, offset)
tuple with an index into the multi-pack index. That index describes
another (pack, offset) tuple, and it is _those_ two tuples that are
compared.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git repack" so far has been only capable of repacking everything
under the sun into a single pack (or split by size). A cleverer
strategy to reduce the cost of repacking a repository has been
introduced.
* tb/geometric-repack:
builtin/pack-objects.c: ignore missing links with --stdin-packs
builtin/repack.c: reword comment around pack-objects flags
builtin/repack.c: be more conservative with unsigned overflows
builtin/repack.c: assign pack split later
t7703: test --geometric repack with loose objects
builtin/repack.c: do not repack single packs with --geometric
builtin/repack.c: add '--geometric' option
packfile: add kept-pack cache for find_kept_pack_entry()
builtin/pack-objects.c: rewrite honor-pack-keep logic
p5303: measure time to repack with keep
p5303: add missing &&-chains
builtin/pack-objects.c: add '--stdin-packs' option
revision: learn '--no-kept-objects'
packfile: introduce 'find_kept_pack_entry()'
Add and apply a semantic patch for converting code that open-codes
CALLOC_ARRAY to use it instead. It shortens the code and infers the
element size automatically.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In a recent patch we added a function 'find_kept_pack_entry()' to look
for an object only among kept packs.
While this function avoids doing any lookup work in non-kept packs, it
is still linear in the number of packs, since we have to traverse the
linked list of packs once per object. Let's cache a reduced version of
that list to save us time.
Note that this cache will last the lifetime of the program. We could
invalidate it on reprepare_packed_git(), but there's not much point in
being rigorous here:
- we might already fail to notice new .keep packs showing up after the
program starts. We only reprepare_packed_git() when we fail to find
an object. But adding a new pack won't cause that to happen.
Somebody repacking could add a new pack and delete an old one, but
most of the time we'd have a descriptor or mmap open to the old
pack anyway, so we might not even notice.
- in pack-objects we already cache the .keep state at startup, since
56dfeb6263 (pack-objects: compute local/ignore_pack_keep early,
2016-07-29). So this is just extending that concept further.
- we don't have to worry about any packed_git being removed; we always
keep the old structs around, even after reprepare_packed_git()
We do defensively invalidate the cache in case the set of kept packs
being asked for changes (e.g., only in-core kept packs were cached, but
suddenly the caller also wants on-disk kept packs, too). In theory we
could build all three caches and switch between them, but it's not
necessary, since this patch (and series) never changes the set of kept
packs that it wants to inspect from the cache.
So that "optimization" is more about being defensive in the face of
future changes than it is about asking for multiple kinds of kept packs
in this patch.
Here are p5303 results (as always, measured against the kernel):
Test HEAD^ HEAD
-----------------------------------------------------------------------------------------------
5303.5: repack (1) 57.34(54.66+10.88) 56.98(54.36+10.98) -0.6%
5303.6: repack with kept (1) 57.38(54.83+10.49) 57.17(54.97+10.26) -0.4%
5303.11: repack (50) 71.70(88.99+4.74) 71.62(88.48+5.08) -0.1%
5303.12: repack with kept (50) 72.58(89.61+4.78) 71.56(88.80+4.59) -1.4%
5303.17: repack (1000) 217.19(491.72+14.25) 217.31(490.82+14.53) +0.1%
5303.18: repack with kept (1000) 246.12(520.07+14.93) 217.08(490.37+15.10) -11.8%
and the --stdin-packs case, which scales a little bit better (although
not by that much even at 1,000 packs):
5303.7: repack with --stdin-packs (1) 0.00(0.00+0.00) 0.00(0.00+0.00) =
5303.13: repack with --stdin-packs (50) 3.43(11.75+0.24) 3.43(11.69+0.30) +0.0%
5303.19: repack with --stdin-packs (1000) 130.50(307.15+7.66) 125.13(301.36+8.04) -4.1%
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>
Future callers will want a function to fill a 'struct pack_entry' for a
given object id but _only_ from its position in any kept pack(s).
In particular, an new 'git repack' mode which ensures the resulting
packs form a geometric progress by object count will mark packs that it
does not want to repack as "kept in-core", and it will want to halt a
reachability traversal as soon as it visits an object in any of the kept
packs. But, it does not want to halt the traversal at non-kept, or
.keep packs.
The obvious alternative is 'find_pack_entry()', but this doesn't quite
suffice since it only returns the first pack it finds, which may or may
not be kept (and the mru cache makes it unpredictable which one you'll
get if there are options).
Short of that, you could walk over all packs looking for the object in
each one, but it scales with the number of packs, which may be
prohibitive.
Introduce 'find_kept_pack_entry()', a function which is like
'find_pack_entry()', but only fills in objects in the kept packs.
Handle packs which have .keep files, as well as in-core kept packs
separately, since certain callers will want to distinguish one from the
other. (Though on-disk and in-core kept packs share the adjective
"kept", it is best to think of the two sets as independent.)
There is a gotcha when looking up objects that are duplicated in kept
and non-kept packs, particularly when the MIDX stores the non-kept
version and the caller asked for kept objects only. This could be
resolved by teaching the MIDX to resolve duplicates by always favoring
the kept pack (if one exists), but this breaks an assumption in existing
MIDXs, and so it would require a format change.
The benefit to changing the MIDX in this way is marginal, so we instead
have a more thorough check here which is explained with a comment.
Callers will be added in subsequent patches.
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Specify the format of the on-disk reverse index 'pack-*.rev' file, as
well as prepare the code for the existence of such files.
The reverse index maps from pack relative positions (i.e., an index into
the array of object which is sorted by their offsets within the
packfile) to their position within the 'pack-*.idx' file. Today, this is
done by building up a list of (off_t, uint32_t) tuples for each object
(the off_t corresponding to that object's offset, and the uint32_t
corresponding to its position in the index). To convert between pack and
index position quickly, this array of tuples is radix sorted based on
its offset.
This has two major drawbacks:
First, the in-memory cost scales linearly with the number of objects in
a pack. Each 'struct revindex_entry' is sizeof(off_t) +
sizeof(uint32_t) + padding bytes for a total of 16.
To observe this, force Git to load the reverse index by, for e.g.,
running 'git cat-file --batch-check="%(objectsize:disk)"'. When asking
for a single object in a fresh clone of the kernel, Git needs to
allocate 120+ MB of memory in order to hold the reverse index in memory.
Second, the cost to sort also scales with the size of the pack.
Luckily, this is a linear function since 'load_pack_revindex()' uses a
radix sort, but this cost still must be paid once per pack per process.
As an example, it takes ~60x longer to print the _size_ of an object as
it does to print that entire object's _contents_:
Benchmark #1: git.compile cat-file --batch <obj
Time (mean ± σ): 3.4 ms ± 0.1 ms [User: 3.3 ms, System: 2.1 ms]
Range (min … max): 3.2 ms … 3.7 ms 726 runs
Benchmark #2: git.compile cat-file --batch-check="%(objectsize:disk)" <obj
Time (mean ± σ): 210.3 ms ± 8.9 ms [User: 188.2 ms, System: 23.2 ms]
Range (min … max): 193.7 ms … 224.4 ms 13 runs
Instead, avoid computing and sorting the revindex once per process by
writing it to a file when the pack itself is generated.
The format is relatively straightforward. It contains an array of
uint32_t's, the length of which is equal to the number of objects in the
pack. The ith entry in this table contains the index position of the
ith object in the pack, where "ith object in the pack" is determined by
pack offset.
One thing that the on-disk format does _not_ contain is the full (up to)
eight-byte offset corresponding to each object. This is something that
the in-memory revindex contains (it stores an off_t in 'struct
revindex_entry' along with the same uint32_t that the on-disk format
has). Omit it in the on-disk format, since knowing the index position
for some object is sufficient to get a constant-time lookup in the
pack-*.idx file to ask for an object's offset within the pack.
This trades off between the on-disk size of the 'pack-*.rev' file for
runtime to chase down the offset for some object. Even though the lookup
is constant time, the constant is heavier, since it can potentially
involve two pointer walks in v2 indexes (one to access the 4-byte offset
table, and potentially a second to access the double wide offset table).
Consider trying to map an object's pack offset to a relative position
within that pack. In a cold-cache scenario, more page faults occur while
switching between binary searching through the reverse index and
searching through the *.idx file for an object's offset. Sure enough,
with a cold cache (writing '3' into '/proc/sys/vm/drop_caches' after
'sync'ing), printing out the entire object's contents is still
marginally faster than printing its size:
Benchmark #1: git.compile cat-file --batch-check="%(objectsize:disk)" <obj >/dev/null
Time (mean ± σ): 22.6 ms ± 0.5 ms [User: 2.4 ms, System: 7.9 ms]
Range (min … max): 21.4 ms … 23.5 ms 41 runs
Benchmark #2: git.compile cat-file --batch <obj >/dev/null
Time (mean ± σ): 17.2 ms ± 0.7 ms [User: 2.8 ms, System: 5.5 ms]
Range (min … max): 15.6 ms … 18.2 ms 45 runs
(Numbers taken in the kernel after cheating and using the next patch to
generate a reverse index). There are a couple of approaches to improve
cold cache performance not pursued here:
- We could include the object offsets in the reverse index format.
Predictably, this does result in fewer page faults, but it triples
the size of the file, while simultaneously duplicating a ton of data
already available in the .idx file. (This was the original way I
implemented the format, and it did show
`--batch-check='%(objectsize:disk)'` winning out against `--batch`.)
On the other hand, this increase in size also results in a large
block-cache footprint, which could potentially hurt other workloads.
- We could store the mapping from pack to index position in more
cache-friendly way, like constructing a binary search tree from the
table and writing the values in breadth-first order. This would
result in much better locality, but the price you pay is trading
O(1) lookup in 'pack_pos_to_index()' for an O(log n) one (since you
can no longer directly index the table).
So, neither of these approaches are taken here. (Thankfully, the format
is versioned, so we are free to pursue these in the future.) But, cold
cache performance likely isn't interesting outside of one-off cases like
asking for the size of an object directly. In real-world usage, Git is
often performing many operations in the revindex (i.e., asking about
many objects rather than a single one).
The trade-off is worth it, since we will avoid the vast majority of the
cost of generating the revindex that the extra pointer chase will look
like noise in the following patch's benchmarks.
This patch describes the format and prepares callers (like in
pack-revindex.c) to be able to read *.rev files once they exist. An
implementation of the writer will appear in the next patch, and callers
will gradually begin to start using the writer in the patches that
follow after that.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Abstract accesses to in-core revindex that allows enumerating
objects stored in a packfile in the order they appear in the pack,
in preparation for introducing an on-disk precomputed revindex.
* tb/pack-revindex-api: (21 commits)
for_each_object_in_pack(): clarify pack vs index ordering
pack-revindex.c: avoid direct revindex access in 'offset_to_pack_pos()'
pack-revindex: hide the definition of 'revindex_entry'
pack-revindex: remove unused 'find_revindex_position()'
pack-revindex: remove unused 'find_pack_revindex()'
builtin/gc.c: guess the size of the revindex
for_each_object_in_pack(): convert to new revindex API
unpack_entry(): convert to new revindex API
packed_object_info(): convert to new revindex API
retry_bad_packed_offset(): convert to new revindex API
get_delta_base_oid(): convert to new revindex API
rebuild_existing_bitmaps(): convert to new revindex API
try_partial_reuse(): convert to new revindex API
get_size_by_pos(): convert to new revindex API
show_objects_for_type(): convert to new revindex API
bitmap_position_packfile(): convert to new revindex API
check_object(): convert to new revindex API
write_reused_pack_verbatim(): convert to new revindex API
write_reused_pack_one(): convert to new revindex API
write_reuse_object(): convert to new revindex API
...
We may return objects in one of two orders: how they appear in the .idx
(sorted by object id) or how they appear in the packfile itself. To
further complicate matters, we have two ordering variables, "i" and
"pos", and it is not clear to which order they apply.
Let's clarify this by using an unambiguous name where possible, and
leaving a comment for the variable that does double-duty.
Signed-off-by: Jeff King <peff@peff.net>
Acked-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Avoid looking at the 'revindex' pointer directly and instead call
'pack_pos_to_index()'.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Remove direct manipulation of the 'struct revindex_entry' type as well
as calls to the deprecated API in 'packfile.c:unpack_entry()'. Usual
clean-up is performed (replacing '->nr' with calls to
'pack_pos_to_index()' and so on).
Add an additional check to make sure that 'obj_offset()' points at a
valid object. In the case this check is violated, we cannot call
'mark_bad_packed_object()' because we don't know the OID. At the top of
the call stack is do_oid_object_info_extended() (via
packed_object_info()), which does mark the object.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Convert another call of 'find_pack_revindex()' to its replacement
'pack_pos_to_offset()'. Likewise:
- Avoid manipulating `struct packed_git`'s `revindex` pointer directly
by removing the pointer-as-array indexing.
- Add an additional guard to check that the offset 'obj_offset()'
points to a real object. This should be the case with well-behaved
callers to 'packed_object_info()', but isn't guarenteed.
Other blocks that fill in various other values from the 'struct
object_info' request handle bad inputs by setting the type to
'OBJ_BAD' and jumping to 'out'. Do the same when given a bad offset
here.
The previous code would have segfaulted when given a bad
'obj_offset' value, since 'find_pack_revindex()' would return
'NULL', and then the line that fills 'oi->disk_sizep' would try to
access 'NULL[1]' with a stride of 16 bytes (the width of 'struct
revindex_entry)'.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Perform exactly the same conversion as in the previous commit to another
caller within 'packfile.c'.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Replace direct accesses to the 'struct revindex' type with a call to
'pack_pos_to_index()'.
Likewise drop the old-style 'find_pack_revindex()' with its replacement
'offset_to_pack_pos()' (while continuing to perform the same error
checking).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Change all remnants of "sha1" in hash-lookup.c and .h and rename them to
reflect that we're not just able to handle SHA-1 these days.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Junio C Hamano
Jeff King
René Scharfe
Taylor Blau
Jonathan Tan
Matt Cooper
Eric Wong
Elijah Newren
Martin Ågren