git/pack-objects.c, branch v2.50.0

pack-objects: free packing_data in more places

2023-12-14T22:38:07Z

The pack-objects internals use a packing_data struct to track what objects are part of the pack(s) being formed. Since these structures contain allocated fields, failing to appropriately free() them results in a leak. Plug that leak by introducing a clear_packing_data() function, and call it in the appropriate spots. This is a fairly straightforward leak to plug, since none of the callers expect to read any values or have any references to parts of the address space being freed. Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano

parse: separate out parsing functions from config.h

2023-09-29T22:14:57Z

The files config.{h,c} contain functions that have to do with parsing, but not config. In order to further reduce all-in-one headers, separate out functions in config.c that do not operate on config into its own file, parse.h, and update the include directives in the .c files that need only such functions accordingly. Signed-off-by: Calvin Wan Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano

git-compat-util: move alloc macros to git-compat-util.h

2023-07-05T18:42:31Z

alloc_nr, ALLOC_GROW, and ALLOC_GROW_BY are commonly used macros for dynamic array allocation. Moving these macros to git-compat-util.h with the other alloc macros focuses alloc.[ch] to allocation for Git objects and additionally allows us to remove inclusions to alloc.h from files that solely used the above macros. Signed-off-by: Calvin Wan Signed-off-by: Junio C Hamano

alloc.h: move ALLOC_GROW() functions from cache.h

2023-02-24T01:25:28Z

This allows us to replace includes of cache.h with includes of the much smaller alloc.h in many places. It does mean that we also need to add includes of alloc.h in a number of C files. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano

pack-mtimes: support writing pack .mtimes files

2022-05-26T22:48:26Z

Now that the `.mtimes` format is defined, supplement the pack-write API to be able to conditionally write an `.mtimes` file along with a pack by setting an additional flag and passing an oidmap that contains the timestamps corresponding to each object in the pack. Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano

use CALLOC_ARRAY

2021-03-14T00:00:09Z

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 Signed-off-by: Junio C Hamano

pack-objects: convert oe_set_delta_ext() to use object_id

2020-02-24T20:55:52Z

We already store an object_id internally, and now our sole caller also has one. Let's stop passing around the internal hash array, which adds a bit of type safety. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano

Merge branch 'jk/optim-in-pack-idx-conversion'

2019-12-01T17:04:38Z

Code clean-up. * jk/optim-in-pack-idx-conversion: pack-objects: avoid pointless oe_map_new_pack() calls

pack-objects: avoid pointless oe_map_new_pack() calls

2019-11-12T04:36:36Z

This patch fixes an extreme slowdown in pack-objects when you have more than 1023 packs. See below for numbers. Since 43fa44fa3b (pack-objects: move in_pack out of struct object_entry, 2018-04-14), we use a complicated system to save some per-object memory. Each object_entry structs gets a 10-bit field to store the index of the pack it's in. We map those indices into pointers using packing_data->in_pack_by_idx, which we initialize at the start of the program. If we have 2^10 or more packs, then we instead create an array of pack pointers, one per object. This is packing_data->in_pack. So far so good. But there's one other tricky case: if a new pack arrives after we've initialized in_pack_by_idx, it won't have an index yet. We solve that by calling oe_map_new_pack(), which just switches on the fly to the less-optimal in_pack mechanism, allocating the array and back-filling it for already-seen objects. But that logic kicks in even when we've switched to it already (whether because we really did see a new pack, or because we had too many packs in the first place). The result doesn't produce a wrong outcome, but it's very slow. What happens is this: - imagine you have a repo with 500k objects and 2000 packs that you want to repack. - before looking at any objects, we call prepare_in_pack_by_idx(). It starts allocating an index for each pack. On the 1024th pack, it sees there are too many, so it bails, leaving in_pack_by_idx as NULL. - while actually adding objects to the packing list, we call oe_set_in_pack(), which checks whether the pack already has an index. If it's one of the packs after the first 1023, then it doesn't have one, and we'll call oe_map_new_pack(). But there's no useful work for that function to do. We're already using in_pack, so it just uselessly walks over the complete list of objects, trying to backfill in_pack. And we end up doing this for almost 1000 packs (each of which may be triggered by more than one object). And each time it triggers, we may iterate over up to 500k objects. So in the absolute worst case, this is quadratic in the number of objects. The solution is simple: we don't need to bother checking whether the pack has an index if we've already converted to using in_pack, since by definition we're not going to use it. So we can just push the "does the pack have a valid index" check down into that half of the conditional, where we know we're going to use it. The current test in p5303 sadly doesn't notice this problem, since it maxes out at 1000 packs. If we add a new test to it at 2000 packs, it does show the improvement: Test HEAD^ HEAD ---------------------------------------------------------------------- 5303.12: repack (2000) 26.72(39.68+0.67) 15.70(28.70+0.66) -41.2% However, these many-pack test cases are rather expensive to run, so adding larger and larger numbers isn't appealing. Instead, we can show it off more easily by using GIT_TEST_FULL_IN_PACK_ARRAY, which forces us into the absolute worst case: no pack has an index, so we'll trigger oe_map_new_pack() pointlessly for every single object, making it truly quadratic. Here are the numbers (on git.git) with the included change to p5303: Test HEAD^ HEAD ---------------------------------------------------------------------- 5303.3: rev-list (1) 2.05(1.98+0.06) 2.06(1.99+0.06) +0.5% 5303.4: repack (1) 33.45(33.46+0.19) 2.75(2.73+0.22) -91.8% 5303.6: rev-list (50) 2.07(2.01+0.06) 2.06(2.01+0.05) -0.5% 5303.7: repack (50) 34.21(35.18+0.16) 3.49(4.50+0.12) -89.8% 5303.9: rev-list (1000) 2.87(2.78+0.08) 2.88(2.80+0.07) +0.3% 5303.10: repack (1000) 41.26(51.30+0.47) 10.75(20.75+0.44) -73.9% Again, those improvements aren't realistic for the 1-pack case (because in the real world, the full-array solution doesn't kick in), but it's more useful to be testing the more-complicated code path. While we're looking at this issue, we'll tweak one more thing: in oe_map_new_pack(), we call REALLOC_ARRAY(pack->in_pack). But we'd never expect to get here unless we're back-filling it for the first time, in which case it would be NULL. So let's switch that to ALLOC_ARRAY() for clarity, and add a BUG() to document the expectation. Unfortunately this code isn't well-covered in the test suite because it's inherently racy (it only kicks in if somebody else adds a new pack while we're in the middle of repacking). Signed-off-by: Jeff King Reviewed-by: Derrick Stolee Signed-off-by: Junio C Hamano

pack-objects: drop packlist index_pos optimization

2019-09-06T18:03:42Z

Once upon a time, the code to add an object to our packing list in pack-objects all lived in a single function. It computed the position within the hash table once, then used it to check if the object was already present, and if not, to add it. Later, in 2834bc27c1 (pack-objects: refactor the packing list, 2013-10-24), this was split into two functions: packlist_find() and packlist_alloc(). We ended up with an "index_pos" variable that gets passed through several functions to make it from one to the other. The resulting code is rather confusing to follow. The "index_pos" variable is sometimes undefined, if we don't yet have a hash table. This works out in practice because in that case packlist_alloc() won't use it at all, since it will have to create/grow the hash table. But it's hard to verify that, and it does cause gcc 9.2.1's -Wmaybe-uninitialized to complain when compiled with "-flto -O3" (rightfully, since we do pass the uninitialized value as a function parameter, even if nobody ends up using it). All of this is to save computing the hash index again when we're inserting into the hash table, which I found doesn't make a measurable difference in the program runtime (which is not surprising, since we're doing all kinds of other heavyweight things for each object). Let's just drop this index_pos variable entirely, simplifying the code (and pleasing the compiler). We might be better still refactoring this custom hash table to use one of our existing implementations (an oidmap, or a kh_oid_map). I stopped short of that here, but this would be the likely first step towards that anyway. Reported-by: Stephan Beyer Signed-off-by: Jeff King Signed-off-by: Junio C Hamano