git/pack-bitmap.h, branch v2.31.2

rev-list: add --disk-usage option for calculating disk usage

2021-02-11T17:57:55Z

It can sometimes be useful to see which refs are contributing to the overall repository size (e.g., does some branch have a bunch of objects not found elsewhere in history, which indicates that deleting it would shrink the size of a clone). You can find that out by generating a list of objects, getting their sizes from cat-file, and then summing them, like: git rev-list --objects --no-object-names main..branch git cat-file --batch-check='%(objectsize:disk)' | perl -lne '$total += $_; END { print $total }' Though note that the caveats from git-cat-file(1) apply here. We "blame" base objects more than their deltas, even though the relationship could easily be flipped. Still, it can be a useful rough measure. But one problem is that it's slow to run. Teaching rev-list to sum up the sizes can be much faster for two reasons: 1. It skips all of the piping of object names and sizes. 2. If bitmaps are in use, for objects that are in the bitmapped packfile we can skip the oid_object_info() lookup entirely, and just ask the revindex for the on-disk size. This patch implements a --disk-usage option which produces the same answer in a fraction of the time. Here are some timings using a clone of torvalds/linux: [rev-list piped to cat-file, no bitmaps] $ time git rev-list --objects --no-object-names --all | git cat-file --buffer --batch-check='%(objectsize:disk)' | perl -lne '$total += $_; END { print $total }' 1459938510 real 0m29.635s user 0m38.003s sys 0m1.093s [internal, no bitmaps] $ time git rev-list --disk-usage --objects --all 1459938510 real 0m31.262s user 0m30.885s sys 0m0.376s Even though the wall-clock time is slightly worse due to parallelism, notice the CPU savings between the two. We saved 21% of the CPU just by avoiding the pipes. But the real win is with bitmaps. If we use them without the new option: [rev-list piped to cat-file, bitmaps] $ time git rev-list --objects --no-object-names --all --use-bitmap-index | git cat-file --batch-check='%(objectsize:disk)' | perl -lne '$total += $_; END { print $total }' 1459938510 real 0m6.244s user 0m8.452s sys 0m0.311s then we're faster to generate the list of objects, but we still spend a lot of time piping and looking things up. But if we do both together: [internal, bitmaps] $ time git rev-list --disk-usage --objects --all --use-bitmap-index 1459938510 real 0m0.219s user 0m0.169s sys 0m0.049s then we get the same answer much faster. For "--all", that answer will correspond closely to "du objects/pack", of course. But we're actually checking reachability here, so we're still fast when we ask for more interesting things: $ time git rev-list --disk-usage --use-bitmap-index v5.0..v5.10 374798628 real 0m0.429s user 0m0.356s sys 0m0.072s Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

pack-bitmap: factor out 'bitmap_for_commit()'

2020-12-08T22:49:04Z

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 Signed-off-by: Junio C Hamano

pack-bitmap-write: ignore BITMAP_FLAG_REUSE

2020-12-08T22:48:17Z

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 Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano

Merge branch 'jk/object-filter-with-bitmap'

2020-03-02T23:07:18Z

The object reachability bitmap machinery and the partial cloning machinery were not prepared to work well together, because some object-filtering criteria that partial clones use inherently rely on object traversal, but the bitmap machinery is an optimization to bypass that object traversal. There however are some cases where they can work together, and they were taught about them. * jk/object-filter-with-bitmap: rev-list --count: comment on the use of count_right++ pack-objects: support filters with bitmaps pack-bitmap: implement BLOB_LIMIT filtering pack-bitmap: implement BLOB_NONE filtering bitmap: add bitmap_unset() function rev-list: use bitmap filters for traversal pack-bitmap: basic noop bitmap filter infrastructure rev-list: allow commit-only bitmap traversals t5310: factor out bitmap traversal comparison rev-list: allow bitmaps when counting objects rev-list: make --count work with --objects rev-list: factor out bitmap-optimized routines pack-bitmap: refuse to do a bitmap traversal with pathspecs rev-list: fallback to non-bitmap traversal when filtering pack-bitmap: fix leak of haves/wants object lists pack-bitmap: factor out type iterator initialization

Merge branch 'jk/packfile-reuse-cleanup'

2020-02-14T20:54:19Z

The way "git pack-objects" reuses objects stored in existing pack to generate its result has been improved. * jk/packfile-reuse-cleanup: pack-bitmap: don't rely on bitmap_git->reuse_objects pack-objects: add checks for duplicate objects pack-objects: improve partial packfile reuse builtin/pack-objects: introduce obj_is_packed() pack-objects: introduce pack.allowPackReuse csum-file: introduce hashfile_total() pack-bitmap: simplify bitmap_has_oid_in_uninteresting() pack-bitmap: uninteresting oid can be outside bitmapped packfile pack-bitmap: introduce bitmap_walk_contains() ewah/bitmap: introduce bitmap_word_alloc() packfile: expose get_delta_base() builtin/pack-objects: report reused packfile objects

pack-bitmap: basic noop bitmap filter infrastructure

2020-02-14T18:46:22Z

Currently you can't use object filters with bitmaps, but we plan to support at least some filters with bitmaps. Let's introduce some infrastructure that will help us do that: - prepare_bitmap_walk() now accepts a list_objects_filter_options parameter (which can be NULL for no filtering; all the current callers pass this) - we'll bail early if the filter is incompatible with bitmaps (just as we would if there were no bitmaps at all). Currently all filters are incompatible. - we'll filter the resulting bitmap; since there are no supported filters yet, this is always a noop. There should be no behavior change yet, but we'll support some actual filters in a future patch. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

rev-list: allow commit-only bitmap traversals

2020-02-14T18:46:22Z

Ever since we added reachability bitmap support, we've been able to use it with rev-list to get the full list of objects, like: git rev-list --objects --use-bitmap-index --all But you can't do so without --objects, since we weren't ready to just show the commits. However, the internals of the bitmap code are mostly ready for this: they avoid opening up trees when walking to fill in the bitmaps. We just need to actually pass in the rev_info to traverse_bitmap_commit_list() so it knows which types to bother triggering our callback for. For completeness, the perf test now covers both the existing --objects case, as well as the new commits-only behavior (the objects one got way faster when we introduced bitmaps, but obviously isn't improved now). Here are numbers for linux.git: Test HEAD^ HEAD ------------------------------------------------------------------------ 5310.7: rev-list (commits) 8.29(8.10+0.19) 1.76(1.72+0.04) -78.8% 5310.8: rev-list (objects) 8.06(7.94+0.12) 8.14(7.94+0.13) +1.0% That run was cheating a little, as I didn't have any commit-graph in the repository, and we'd built it by default these days when running git-gc. Here are numbers with a commit-graph: Test HEAD^ HEAD ------------------------------------------------------------------------ 5310.7: rev-list (commits) 0.70(0.58+0.12) 0.51(0.46+0.04) -27.1% 5310.8: rev-list (objects) 6.20(6.09+0.10) 6.27(6.16+0.11) +1.1% Still an improvement, but a lot less impressive. We could have the perf script remove any commit-graph to show the out-sized effect, but it probably makes sense to leave it in what would be a more typical setup. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

pack-objects: improve partial packfile reuse

2020-01-23T18:51:50Z

The old code to reuse deltas from an existing packfile just tried to dump a whole segment of the pack verbatim. That's faster than the traditional way of actually adding objects to the packing list, but it didn't kick in very often. This new code is really going for a middle ground: do _some_ per-object work, but way less than we'd traditionally do. The general strategy of the new code is to make a bitmap of objects from the packfile we'll include, and then iterate over it, writing out each object exactly as it is in our on-disk pack, but _not_ adding it to our packlist (which costs memory, and increases the search space for deltas). One complication is that if we're omitting some objects, we can't set a delta against a base that we're not sending. So we have to check each object in try_partial_reuse() to make sure we have its delta. About performance, in the worst case we might have interleaved objects that we are sending or not sending, and we'd have as many chunks as objects. But in practice we send big chunks. For instance, packing torvalds/linux on GitHub servers now reused 6.5M objects, but only needed ~50k chunks. Helped-by: Jonathan Tan Signed-off-by: Jeff King Signed-off-by: Christian Couder Signed-off-by: Junio C Hamano

pack-bitmap: introduce bitmap_walk_contains()

2020-01-23T18:51:50Z

We will use this helper function in a following commit to tell us if an object is packed. Signed-off-by: Jeff King Signed-off-by: Christian Couder Signed-off-by: Junio C Hamano

pack-bitmap.h: remove magic number

2019-09-28T05:04:20Z

When we ran `make hdr-check` with the following patch diff --git a/Makefile b/Makefile index f879697ea3..d8df4e316b 100644 --- a/Makefile +++ b/Makefile @@ -2773,7 +2773,7 @@ CHK_HDRS = $(filter-out $(EXCEPT_HDRS),$(patsubst ./%,%,$(LIB_H))) HCO = $(patsubst %.h,%.hco,$(CHK_HDRS)) $(HCO): %.hco: %.h FORCE - $(QUIET_HDR)$(CC) -include git-compat-util.h -I. -o /dev/null -c -xc $< + $(QUIET_HDR)$(CC) -include git-compat-util.h -I. -o /dev/null -c -xc $(ALL_CFLAGS) $< .PHONY: hdr-check $(HCO) hdr-check: $(HCO) and with `DEVELOPER=1`, we got the following warning on Arch Linux: pack-bitmap.h:20:19: error: ‘BITMAP_IDX_SIGNATURE’ defined but not used [-Werror=unused-const-variable=] 20 | static const char BITMAP_IDX_SIGNATURE[] = {'B', 'I', 'T', 'M'}; | ^~~~~~~~~~~~~~~~~~~~ cc1: all warnings being treated as errors "Use" the BITMAP_IDX_SIGNATURE variable by making the size of bitmap_disk_header.magic equal to the size of BITMAP_IDX_SIGNATURE, thereby eliminating the magic number (4). An alternative was to simply add MAYBE_UNUSED, however that does not eliminate the magic number. Another alternative was to change the definition to extern const char BITMAP_IDX_SIGNATURE[4]; However, this design was also not chosen as the static definition allows us to keep the declaration together for readability along with removing the magic number. Signed-off-by: Denton Liu Signed-off-by: Junio C Hamano