git/object-file.c, branch v2.33.6

Merge branch 'cb/many-alternate-optim-fixup'

2021-08-11T19:36:17Z

Build fix. * cb/many-alternate-optim-fixup: object-file: use unsigned arithmetic with bit mask object-store: avoid extra ';' from KHASH_INIT oidtree: avoid nested struct oidtree_node

object-file: use unsigned arithmetic with bit mask

2021-08-11T17:19:56Z

33f379eee6 (make object_directory.loose_objects_subdir_seen a bitmap, 2021-07-07) replaced a wasteful 256-byte array with a 32-byte array and bit operations. The mask calculation shifts a literal 1 of type int left by anything between 0 and 31. UndefinedBehaviorSanitizer doesn't like that and reports: object-file.c:2477:18: runtime error: left shift of 1 by 31 places cannot be represented in type 'int' Make sure to use an unsigned 1 instead to avoid the issue. Signed-off-by: René Scharfe Signed-off-by: Junio C Hamano

Merge branch 'ew/many-alternate-optim'

2021-07-28T20:17:57Z

Optimization for repositories with many alternate object store. * ew/many-alternate-optim: oidtree: a crit-bit tree for odb_loose_cache oidcpy_with_padding: constify `src' arg make object_directory.loose_objects_subdir_seen a bitmap avoid strlen via strbuf_addstr in link_alt_odb_entry speed up alt_odb_usable() with many alternates

Merge branch 'jt/partial-clone-submodule-1'

2021-07-17T00:42:53Z

Prepare the internals for lazily fetching objects in submodules from their promisor remotes. * jt/partial-clone-submodule-1: promisor-remote: teach lazy-fetch in any repo run-command: refactor subprocess env preparation submodule: refrain from filtering GIT_CONFIG_COUNT promisor-remote: support per-repository config repository: move global r_f_p_c to repo struct

oidtree: a crit-bit tree for odb_loose_cache

2021-07-08T04:28:04Z

This saves 8K per `struct object_directory', meaning it saves around 800MB in my case involving 100K alternates (half or more of those alternates are unlikely to hold loose objects). This is implemented in two parts: a generic, allocation-free `cbtree' and the `oidtree' wrapper on top of it. The latter provides allocation using alloc_state as a memory pool to improve locality and reduce free(3) overhead. Unlike oid-array, the crit-bit tree does not require sorting. Performance is bound by the key length, for oidtree that is fixed at sizeof(struct object_id). There's no need to have 256 oidtrees to mitigate the O(n log n) overhead like we did with oid-array. Being a prefix trie, it is natively suited for expanding short object IDs via prefix-limited iteration in `find_short_object_filename'. On my busy workstation, p4205 performance seems to be roughly unchanged (+/-8%). Startup with 100K total alternates with no loose objects seems around 10-20% faster on a hot cache. (800MB in memory savings means more memory for the kernel FS cache). The generic cbtree implementation does impose some extra overhead for oidtree in that it uses memcmp(3) on "struct object_id" so it wastes cycles comparing 12 extra bytes on SHA-1 repositories. I've not yet explored reducing this overhead, but I expect there are many places in our code base where we'd want to investigate this. More information on crit-bit trees: https://cr.yp.to/critbit.html Signed-off-by: Eric Wong Signed-off-by: Junio C Hamano

make object_directory.loose_objects_subdir_seen a bitmap

2021-07-08T04:27:58Z

There's no point in using 8 bits per-directory when 1 bit will do. This saves us 224 bytes per object directory, which ends up being 22MB when dealing with 100K alternates. Signed-off-by: Eric Wong Signed-off-by: Junio C Hamano

avoid strlen via strbuf_addstr in link_alt_odb_entry

2021-07-08T04:27:56Z

We can save a few milliseconds (across 100K odbs) by using strbuf_addbuf() instead of strbuf_addstr() by passing `entry' as a strbuf pointer rather than a "const char *". Signed-off-by: Eric Wong Signed-off-by: Junio C Hamano

speed up alt_odb_usable() with many alternates

2021-07-08T00:21:12Z

With many alternates, the duplicate check in alt_odb_usable() wastes many cycles doing repeated fspathcmp() on every existing alternate. Use a khash to speed up lookups by odb->path. Since the kh_put_* API uses the supplied key without duplicating it, we also take advantage of it to replace both xstrdup() and strbuf_release() in link_alt_odb_entry() with strbuf_detach() to avoid the allocation and copy. In a test repository with 50K alternates and each of those 50K alternates having one alternate each (for a total of 100K total alternates); this speeds up lookup of a non-existent blob from over 16 minutes to roughly 2.7 seconds on my busy workstation. Note: all underlying git object directories were small and unpacked with only loose objects and no packs. Having to load packs increases times significantly. Signed-off-by: Eric Wong Signed-off-by: Junio C Hamano

xmmap: inform Linux users of tuning knobs on ENOMEM

2021-06-30T06:14:25Z

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 Signed-off-by: Junio C Hamano

promisor-remote: teach lazy-fetch in any repo

2021-06-28T16:58:01Z

This is one step towards supporting partial clone submodules. Even after this patch, we will still lack partial clone submodules support, primarily because a lot of Git code that accesses submodule objects does so by adding their object stores as alternates, meaning that any lazy fetches that would occur in the submodule would be done based on the config of the superproject, not of the submodule. This also prevents testing of the functionality in this patch by user-facing commands. So for now, test this mechanism using a test helper. Besides that, there is some code that uses the wrapper functions like has_promisor_remote(). Those will need to be checked to see if they could support the non-wrapper functions instead (and thus support any repository, not just the_repository). Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano Reviewed-by: Elijah Newren Signed-off-by: Junio C Hamano