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authorPhillip Wood <phillip.wood@dunelm.org.uk>2021-09-23 15:26:21 (GMT)
committerJunio C Hamano <gitster@pobox.com>2021-09-24 15:56:28 (GMT)
commit2b88fe0603a93314b96f94b22e197b7b1b838c80 (patch)
treea71bf8e4ffd0df7677844c8f53e9261dc97d3e70
parentdfa8bae5a20ead0737413fec5c7bb754fe538abe (diff)
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rebase: fix todo-list rereading
54fd3243da ("rebase -i: reread the todo list if `exec` touched it", 2017-04-26) sought to reread the todo list after running an exec command only if it had been changed. To accomplish this it checks the stat data of the todo list after running an exec command to see if it has changed. Unfortunately there are two problems, firstly the implementation is buggy we actually reread the list after each exec which is quadratic in the number of commit lookups and secondly the design is predicated on using nanosecond time stamps which are not the default. The implementation bug stems from the fact that we write a new todo list to disk before running each command but do not update the stat data to reflect this[1]. The design problem is that it is possible for the user to edit the todo list without changing its size or inode which means we have to rely on the mtime to tell us if it has changed. Unfortunately unless git is built with USE_NSEC it is possible for the original and edited list to share the same mtime. Ideally "git rebase --edit-todo" would set a flag that we would then check in sequencer.c. Unfortunately this is approach will not work as there are scripts in the wild that write to the todo list directly without running "git rebase --edit-todo". Instead of relying on stat data this patch simply reads the possibly edited todo list and compares it to the original with memcmp(). This is much faster than reparsing the todo list each time. This patch reduces the time to run git rebase -r -xtrue v2.32.0~100 v2.32.0 which runs 419 exec commands by 6.6%. For comparison fixing the implementation bug in stat based approach reduces the time by a further 1.4% and is indistinguishable from never rereading the todo list. [1] https://lore.kernel.org/git/20191125131833.GD23183@szeder.dev/ Reported-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>
-rw-r--r--sequencer.c19
-rw-r--r--sequencer.h1
2 files changed, 8 insertions, 12 deletions
diff --git a/sequencer.c b/sequencer.c
index a248c88..d51440d 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2671,7 +2671,6 @@ static int read_populate_todo(struct repository *r,
struct todo_list *todo_list,
struct replay_opts *opts)
{
- struct stat st;
const char *todo_file = get_todo_path(opts);
int res;
@@ -2679,11 +2678,6 @@ static int read_populate_todo(struct repository *r,
if (strbuf_read_file_or_whine(&todo_list->buf, todo_file) < 0)
return -1;
- res = stat(todo_file, &st);
- if (res)
- return error(_("could not stat '%s'"), todo_file);
- fill_stat_data(&todo_list->stat, &st);
-
res = todo_list_parse_insn_buffer(r, todo_list->buf.buf, todo_list);
if (res) {
if (is_rebase_i(opts))
@@ -4258,12 +4252,14 @@ static int reread_todo_if_changed(struct repository *r,
struct todo_list *todo_list,
struct replay_opts *opts)
{
- struct stat st;
+ int offset;
+ struct strbuf buf = STRBUF_INIT;
- if (stat(get_todo_path(opts), &st)) {
- return error_errno(_("could not stat '%s'"),
- get_todo_path(opts));
- } else if (match_stat_data(&todo_list->stat, &st)) {
+ if (strbuf_read_file_or_whine(&buf, get_todo_path(opts)) < 0)
+ return -1;
+ offset = get_item_line_offset(todo_list, todo_list->current + 1);
+ if (buf.len != todo_list->buf.len - offset ||
+ memcmp(buf.buf, todo_list->buf.buf + offset, buf.len)) {
/* Reread the todo file if it has changed. */
todo_list_release(todo_list);
if (read_populate_todo(r, todo_list, opts))
@@ -4271,6 +4267,7 @@ static int reread_todo_if_changed(struct repository *r,
/* `current` will be incremented on return */
todo_list->current = -1;
}
+ strbuf_release(&buf);
return 0;
}
diff --git a/sequencer.h b/sequencer.h
index d57d8ea..cdeb0c6 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -116,7 +116,6 @@ struct todo_list {
struct todo_item *items;
int nr, alloc, current;
int done_nr, total_nr;
- struct stat_data stat;
};
#define TODO_LIST_INIT { STRBUF_INIT }