@matheusbsbs / matheus-bagliano / commits / 48513e05e2

stash: reuse cached index entries in --patch temporary index

`git stash -p` prepares the interactive selection by creating a temporary index at HEAD, switching `GIT_INDEX_FILE` to it, and then running the `add -p` machinery. That temporary index was created by running `git read-tree HEAD`. The resulting index had no useful cached stat data or fsmonitor-valid bits from the real index. When `run_add_p()` refreshed that temporary index before showing the first prompt, it could end up lstat(2)-ing every tracked file, even in a repository where `git diff` and `git restore -p` can use fsmonitor to avoid that work. Create the temporary index in-process instead. Use `unpack_trees()` to reset the real index contents to HEAD while writing the result to the temporary index path. For paths whose index entries already match HEAD, `oneway_merge()` reuses the existing cache entries, preserving their cached stat data and `CE_FSMONITOR_VALID` state. This makes the refresh performed by `run_add_p()` behave like the one used by `git restore -p`: unchanged paths can be skipped via fsmonitor instead of being scanned again. In a 206k file repository with `core.fsmonitor` enabled and a one-line change in one file, time to first prompt dropped from 34.774 seconds to 0.659 seconds. The new perf test file demonstrates similar improvements, with maen times for without- and with-fsmonitor cases dropping from 6.90 and 6.83 seconds to 0.55 and 0.28 seconds, respectively. Signed-off-by: Adam Johnson <me@adamj.eu> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Adam Johnson committed May 22, 2026 at 23:12 UTC 48513e05e2f226c85a9b88893630c8ae28409772

2 files changed +107 -6

builtin/stash.c

+64 -6

@@ -372,6 +372,56 @@ static int reset_tree(struct object_id *i_tree, int update, int reset)

372 return 0;

373 }

374

375 +static int create_index_from_tree(const struct object_id *tree_id,

376 + const char *index_path)

377 +{

378 + int nr_trees = 1;

379 + int ret = 0;

380 + struct unpack_trees_options opts;

381 + struct tree_desc t[MAX_UNPACK_TREES];

382 + struct tree *tree;

383 + struct index_state dst_istate = INDEX_STATE_INIT(the_repository);

384 + struct lock_file lock_file = LOCK_INIT;

385 +

386 + repo_read_index_preload(the_repository, NULL, 0);

387 + refresh_index(the_repository->index, REFRESH_QUIET, NULL, NULL, NULL);

388 +

389 + hold_lock_file_for_update(&lock_file, index_path, LOCK_DIE_ON_ERROR);

390 +

391 + memset(&opts, 0, sizeof(opts));

392 +

393 + tree = repo_parse_tree_indirect(the_repository, tree_id);

394 + if (!tree || repo_parse_tree(the_repository, tree)) {

395 + ret = -1;

396 + goto done;

397 + }

398 +

399 + init_tree_desc(t, &tree->object.oid, tree->buffer, tree->size);

400 +

401 + opts.head_idx = 1;

402 + opts.src_index = the_repository->index;

403 + opts.dst_index = &dst_istate;

404 + opts.merge = 1;

405 + opts.reset = UNPACK_RESET_PROTECT_UNTRACKED;

406 + opts.fn = oneway_merge;

407 +

408 + if (unpack_trees(nr_trees, t, &opts)) {

409 + ret = -1;

410 + goto done;

411 + }

412 +

413 + if (write_locked_index(&dst_istate, &lock_file, COMMIT_LOCK)) {

414 + ret = error(_("unable to write new index file"));

415 + goto done;

416 + }

417 +

418 +done:

419 + release_index(&dst_istate);

420 + if (ret)

421 + rollback_lock_file(&lock_file);

422 + return ret;

423 +}

424 +

425 static int diff_tree_binary(struct strbuf *out, struct object_id *w_commit)

426 {

427 struct child_process cp = CHILD_PROCESS_INIT;

@@ -1309,18 +1359,26 @@ static int stash_patch(struct stash_info *info, const struct pathspec *ps,

1359 struct interactive_options *interactive_opts)

1360 {

1361 int ret = 0;

1312 - struct child_process cp_read_tree = CHILD_PROCESS_INIT;

1362 struct child_process cp_diff_tree = CHILD_PROCESS_INIT;

1363 + struct commit *head_commit;

1364 + const struct object_id *head_tree;

1365 struct index_state istate = INDEX_STATE_INIT(the_repository);

1366 char *old_index_env = NULL, *old_repo_index_file;

1367

1368 remove_path(stash_index_path.buf);

1369

1319 - cp_read_tree.git_cmd = 1;

1320 - strvec_pushl(&cp_read_tree.args, "read-tree", "HEAD", NULL);

1321 - strvec_pushf(&cp_read_tree.env, "GIT_INDEX_FILE=%s",

1322 - stash_index_path.buf);

1323 - if (run_command(&cp_read_tree)) {

1370 + head_commit = lookup_commit(the_repository, &info->b_commit);

1371 + if (!head_commit || repo_parse_commit(the_repository, head_commit)) {

1372 + ret = -1;

1373 + goto done;

1374 + }

1375 + head_tree = get_commit_tree_oid(head_commit);

1376 + if (!head_tree) {

1377 + ret = -1;

1378 + goto done;

1379 + }

1380 +

1381 + if (create_index_from_tree(head_tree, stash_index_path.buf)) {

1382 ret = -1;

1383 goto done;

1384 }

t/perf/p3904-stash-patch.sh new

+43

@@ -0,0 +1,43 @@

1 +#!/bin/sh

2 +

3 +test_description="Performance tests for git stash -p"

4 +

5 +. ./perf-lib.sh

6 +

7 +test_perf_fresh_repo

8 +

9 +test_expect_success "setup" '

10 + mkdir files &&

11 + test_seq 1 100000 | while read i; do

12 + echo "content $i" >files/$i.txt || return 1

13 + done &&

14 + git add files/ &&

15 + git commit -q -m "add tracked files" &&

16 + echo modified >files/1.txt

17 +'

18 +

19 +test_perf "stash -p, no fsmonitor" \

20 + --setup 'echo modified >files/1.txt' '

21 + printf "q\n" | git stash -p >/dev/null 2>&1 || true

22 +'

23 +

24 +if test_have_prereq FSMONITOR_DAEMON

25 +then

26 + test_expect_success "enable builtin fsmonitor" '

27 + git config core.fsmonitor true &&

28 + git fsmonitor--daemon start &&

29 + git update-index --fsmonitor &&

30 + git status >/dev/null 2>&1

31 + '

32 +

33 + test_perf "stash -p, builtin fsmonitor" \

34 + --setup 'echo modified >files/1.txt && git status >/dev/null 2>&1' '

35 + printf "q\n" | git stash -p >/dev/null 2>&1 || true

36 + '

37 +

38 + test_expect_success "stop builtin fsmonitor" '

39 + git fsmonitor--daemon stop

40 + '

41 +fi

42 +

43 +test_done