git/pack-bitmap.h, branch v2.20.2

bitmap_has_sha1_in_uninteresting(): drop BUG check

2018-09-04T15:30:48Z

Commit 30cdc33fba (pack-bitmap: save "have" bitmap from walk, 2018-08-21) introduced a new function for looking at the "have" side of a bitmap walk. Because it only makes sense to do so after we've finished the walk, we added an extra safety assertion, making sure that bitmap_git->result is non-NULL. However, this safety is misguided. It was trying to catch the case where we had called prepare_bitmap_walk() to give us a "struct bitmap_index", but had not yet called traverse_bitmap_commit_list() to walk it. But all of the interesting computation (including setting up the result and "have" bitmaps) happens in the first function! The latter function only delivers the result to a callback function. So the case we were worried about is impossible; if you get a non-NULL result from prepare_bitmap_walk(), then its "have" field will be fully formed. But much worse, traverse_bitmap_commit_list() actually frees the result field as it finishes. Which means that this assertion is worse than useless: it's almost guaranteed to trigger! Our test suite didn't catch this because the function isn't actually exercised at all. The only caller comes from 6a1e32d532 (pack-objects: reuse on-disk deltas for thin "have" objects, 2018-08-21), and that's triggered only when you fetch or push history that contains an object with a base that is found deep in history. Our test suite fetches and pushes either don't use bitmaps, or use too-small example repositories. But any reasonably-sized real-world push or fetch (with bitmaps) would trigger this. This patch drops the harmful assertion and tweaks the docstring for the function to make the precondition clear. The tests need to be improved to exercise this new pack-objects feature, but we'll do that in a separate commit. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

pack-bitmap: save "have" bitmap from walk

2018-08-21T19:33:39Z

When we do a bitmap walk, we save the result, which represents (WANTs & ~HAVEs); i.e., every object we care about visiting in our walk. However, we throw away the haves bitmap, which can sometimes be useful, too. Save it and provide an access function so code which has performed a walk can query it. A few notes on the accessor interface: - the bitmap code calls these "haves" because it grew out of the want/have negotiation for fetches. But really, these are simply the objects that would be flagged UNINTERESTING in a regular traversal. Let's use that more universal nomenclature for the external module interface. We may want to change the internal naming inside the bitmap code, but that's outside the scope of this patch. - it still uses a bare "sha1" rather than "oid". That's true of all of the bitmap code. And in this particular instance, our caller in pack-objects is dealing with the bare sha1 that comes from a packed REF_DELTA (we're pointing directly to the mmap'd pack on disk). That's something we'll have to deal with as we transition to a new hash, but we can wait and see how the caller ends up being fixed and adjust this interface accordingly. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

Add missing includes and forward declarations

2018-08-15T18:52:09Z

I looped over the toplevel header files, creating a temporary two-line C program for each consisting of #include "git-compat-util.h" #include $HEADER This patch is the result of manually fixing errors in compiling those tiny programs. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano

pack-bitmap: add free function

2018-06-21T19:22:48Z

Add a function to free struct bitmap_index instances, and use it where needed (except when rebuild_existing_bitmaps() is used, since it creates references to the bitmaps within the struct bitmap_index passed to it). Note that the hashes field in struct bitmap_index is not freed because it points to another field within the same struct. The documentation for that field has been updated to clarify that. Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano

pack-bitmap: remove bitmap_git global variable

2018-06-21T18:17:39Z

Remove the bitmap_git global variable. Instead, generate on demand an instance of struct bitmap_index for code that needs to access it. This allows us significant control over the lifetime of instances of struct bitmap_index. In particular, packs can now be closed without worrying if an unnecessarily long-lived "pack" field in struct bitmap_index still points to it. The bitmap API is also clearer in that we need to first obtain a struct bitmap_index, then we use it. This patch raises two potential issues: (1) memory for the struct bitmap_index is allocated without being freed, and (2) prepare_bitmap_git() and prepare_bitmap_walk() can reuse a previously loaded bitmap. For (1), this will be dealt with in a subsequent patch in this patch set that also deals with freeing the contents of the struct bitmap_index (which were not freed previously, because they have global scope). For (2), current bitmap users only load the bitmap once at most (note that pack-objects can use bitmaps or write bitmaps, but not both at the same time), so support for reuse has no effect - and future users can pass around the struct bitmap_index * obtained if they need to do 2 or more things with the same bitmap. Helped-by: Stefan Beller Signed-off-by: Jonathan Tan Helped-by: Jeff King Signed-off-by: Junio C Hamano

pack-objects: move in_pack_pos out of struct object_entry

2018-04-16T03:38:58Z

This field is only need for pack-bitmap, which is an optional feature. Move it to a separate array that is only allocated when pack-bitmap is used (like objects[], it is not freed, since we need it until the end of the process) Signed-off-by: Nguyễn Thái Ngọc Duy Signed-off-by: Junio C Hamano

pack-bitmap: convert traverse_bitmap_commit_list to object_id

2017-10-16T02:05:51Z

Convert traverse_bitmap_commit_list and the callbacks it takes to use a pointer to struct object_id. Signed-off-by: brian m. carlson Signed-off-by: Junio C Hamano

pack-bitmap.c: make pack_bitmap_filename() static

2015-01-15T19:04:10Z

Reviewed-by: Jeff King Signed-off-by: Junio C Hamano

pack-bitmap: do not use gcc packed attribute

2014-12-01T02:07:34Z

The "__attribute__" flag may be a noop on some compilers. That's OK as long as the code is correct without the attribute, but in this case it is not. We would typically end up with a struct that is 2 bytes too long due to struct padding, breaking both reading and writing of bitmaps. Instead of marshalling the data in a struct, let's just provide helpers for reading and writing the appropriate types. Besides being correct on all platforms, the result is more efficient and simpler to read. Signed-off-by: Karsten Blees Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

pack-bitmap: implement optional name_hash cache

2013-12-30T20:19:23Z

When we use pack bitmaps rather than walking the object graph, we end up with the list of objects to include in the packfile, but we do not know the path at which any tree or blob objects would be found. In a recently packed repository, this is fine. A fetch would use the paths only as a heuristic in the delta compression phase, and a fully packed repository should not need to do much delta compression. As time passes, though, we may acquire more objects on top of our large bitmapped pack. If clients fetch frequently, then they never even look at the bitmapped history, and all works as usual. However, a client who has not fetched since the last bitmap repack will have "have" tips in the bitmapped history, but "want" newer objects. The bitmaps themselves degrade gracefully in this circumstance. We manually walk the more recent bits of history, and then use bitmaps when we hit them. But we would also like to perform delta compression between the newer objects and the bitmapped objects (both to delta against what we know the user already has, but also between "new" and "old" objects that the user is fetching). The lack of pathnames makes our delta heuristics much less effective. This patch adds an optional cache of the 32-bit name_hash values to the end of the bitmap file. If present, a reader can use it to match bitmapped and non-bitmapped names during delta compression. Here are perf results for p5310: Test origin/master HEAD^ HEAD ------------------------------------------------------------------------------------------------- 5310.2: repack to disk 36.81(37.82+1.43) 47.70(48.74+1.41) +29.6% 47.75(48.70+1.51) +29.7% 5310.3: simulated clone 30.78(29.70+2.14) 1.08(0.97+0.10) -96.5% 1.07(0.94+0.12) -96.5% 5310.4: simulated fetch 3.16(6.10+0.08) 3.54(10.65+0.06) +12.0% 1.70(3.07+0.06) -46.2% 5310.6: partial bitmap 36.76(43.19+1.81) 6.71(11.25+0.76) -81.7% 4.08(6.26+0.46) -88.9% You can see that the time spent on an incremental fetch goes down, as our delta heuristics are able to do their work. And we save time on the partial bitmap clone for the same reason. Signed-off-by: Vicent Marti Signed-off-by: Jeff King Signed-off-by: Junio C Hamano