Subject: [PATCH v4 1/2] string-list: use ALLOC_GROW macro when reallocing string_list

From: [email-masked]
Date: Tue, 11 Apr 2017 20:08:01 +0000

From: Jeff Hostetler <[email-masked]>

Use ALLOC_GROW() macro when reallocing a string_list array
rather than simply increasing it by 32.  This is a performance
optimization.

During status on a very large repo and there are many changes,
a significant percentage of the total run time is spent
reallocing the wt_status.changes array.

This change decreases the time in wt_status_collect_changes_worktree()
from 125 seconds to 45 seconds on my very large repository.

This produced a modest gain on my 1M file artificial repo, but
broke even on linux.git.

Test                                            HEAD^^            HEAD
---------------------------------------------------------------------------------------
0005.2: read-tree status br_ballast (1000001)   8.29(5.62+2.62)   8.22(5.57+2.63) -0.8%

Signed-off-by: Jeff Hostetler <[email-masked]>
---
 string-list.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/string-list.c b/string-list.c
index 45016ad..003ca18 100644
--- a/string-list.c
+++ b/string-list.c
@@ -41,10 +41,7 @@ static int add_entry(int insert_at, struct string_list *list, const char *string
 	if (exact_match)
 		return -1 - index;
 
-	if (list->nr + 1 >= list->alloc) {
-		list->alloc += 32;
-		REALLOC_ARRAY(list->items, list->alloc);
-	}
+	ALLOC_GROW(list->items, list->nr+1, list->alloc);
 	if (index < list->nr)
 		memmove(list->items + index + 1, list->items + index,
 				(list->nr - index)
-- 
2.9.3