[PATCH] read-tree --aggressive
From: Junio C Hamano <hidden>
Date: 2016-06-15 22:42:18
Subsystem:
the rest · Maintainer:
Linus Torvalds
"Peter Eriksen" [off-list ref] writes:
In connection with Ian Molton's question about merge have I played a little with 'git merge' on the kernel sources. What I find is that a merge can take quite some time, but I'm not sure where that time exactly goes to. Here are the times I got: Recursive (default): 4m22.282s Resolve (-s resolve): 3m23.548s
In your sample script, you do not disable the post-merge diff,
which is typically one of the most expensive part in the whole
merge, and I am wondering how fast a machine you are using to
get 4 minutes. The post-merge diff is generated by piping the
output of 'diff-tree -M' to 'apply --stat --summary', and that
step alone takes about 12 minutes wallclock time on my box X-<.
Since my box is not as fast as yours, I've eliminated the
post-merge diff step and tried your final merge step like this:
$ time git merge --no-summary -s resolve \
'Merging happily' HEAD v2.6.15 >/dev/null
and got this:
real 2m15.737s
user 1m43.320s
sys 0m26.690s
With the attached patch, the most expensive part, which is the
repeated invocation of git-merge-one-file to remove many deleted
paths, is eliminated. The result is this.
real 0m20.311s
user 0m15.780s
sys 0m4.150s
This patch would not help recursive strategy, though. Calling
read-tree with --aggressive flag essentially disables the
benefit we would expect to get from it -- rename detection.
-- >8 --
A new flag --aggressive resolves what we traditionally resolved
with external git-merge-one-file inside index while read-tree
3-way merge works.
git-merge-octopus and git-merge-resolve use this flag before
running git-merge-index with git-merge-one-file.
Signed-off-by: Junio C Hamano <redacted>
---
git-merge-octopus.sh | 2 +-
git-merge-resolve.sh | 2 +-
read-tree.c | 32 ++++++++++++++++++++++++++++++++
3 files changed, 34 insertions(+), 2 deletions(-)
2a4bb6bc618bdad6529d9ffe361bc8b7dd28a56cdiff --git a/git-merge-octopus.sh b/git-merge-octopus.sh
index eb74f96..eb3f473 100755
--- a/git-merge-octopus.sh
+++ b/git-merge-octopus.sh@@ -90,7 +90,7 @@ do NON_FF_MERGE=1 echo "Trying simple merge with $SHA1" - git-read-tree -u -m $common $MRT $SHA1 || exit 2 + git-read-tree -u -m --aggressive $common $MRT $SHA1 || exit 2 next=$(git-write-tree 2>/dev/null) if test $? -ne 0 then
diff --git a/git-merge-resolve.sh b/git-merge-resolve.sh
index 966e81f..0a8ef21 100755
--- a/git-merge-resolve.sh
+++ b/git-merge-resolve.sh@@ -38,7 +38,7 @@ then fi git-update-index --refresh 2>/dev/null -git-read-tree -u -m $bases $head $remotes || exit 2 +git-read-tree -u -m --aggressive $bases $head $remotes || exit 2 echo "Trying simple merge." if result_tree=$(git-write-tree 2>/dev/null) then
diff --git a/read-tree.c b/read-tree.c
index a46c6fe..5580f15 100644
--- a/read-tree.c
+++ b/read-tree.c@@ -15,6 +15,7 @@ static int update = 0; static int index_only = 0; static int nontrivial_merge = 0; static int trivial_merges_only = 0; +static int aggressive = 0; static int head_idx = -1; static int merge_size = 0;
@@ -424,11 +425,14 @@ static int threeway_merge(struct cache_e int df_conflict_remote = 0; int any_anc_missing = 0; + int no_anc_exists = 1; int i; for (i = 1; i < head_idx; i++) { if (!stages[i]) any_anc_missing = 1; + else + no_anc_exists = 0; } index = stages[0];
@@ -489,6 +493,29 @@ static int threeway_merge(struct cache_e if (!head && !remote && any_anc_missing) return 0; + /* Under the new "aggressive" rule, we resolve mostly trivial + * cases that we historically had git-merge-one-file resolve. + */ + if (aggressive) { + int head_deleted = !head && !df_conflict_head; + int remote_deleted = !remote && !df_conflict_remote; + /* + * Deleted in both. + * Deleted in one and unchanged in the other. + */ + if ((head_deleted && remote_deleted) || + (head_deleted && remote && remote_match) || + (remote_deleted && head && head_match)) + return 0; + + /* + * Added in both, identically. + */ + if (no_anc_exists && head && remote && same(head, remote)) + return merged_entry(head, index); + + } + /* Below are "no merge" cases, which require that the index be * up-to-date to avoid the files getting overwritten with * conflict resolution files.
@@ -677,6 +704,11 @@ int main(int argc, char **argv) continue; } + if (!strcmp(arg, "--aggressive")) { + aggressive = 1; + continue; + } + /* "-m" stands for "merge", meaning we start in stage 1 */ if (!strcmp(arg, "-m")) { if (stage || merge)
--
1.1.6.ge2129