[PATCH] blame.c: don't drop origin blobs as eagerly

From: David Kastrup <dak@gnu.org>
Date: May 27, 2016, 13:35 UTC
Message-ID: <1464356141-3797-1-git-send-email-dak@gnu.org>

When a parent blob already has chunks queued up for blaming, dropping the blob at the end of one blame step will cause it to get reloaded right away, doubling the amount of I/O and unpacking when processing a linear history.

Keeping such parent blobs in memory seems like a reasonable
optimization.  It's conceivable that this may incur additional memory
pressure particularly when the history contains lots of merges from
long-diverged branches.  In practice, this optimization appears to
behave quite benignly, and a viable strategy for limiting the total
amount of cached blobs in a useful manner seems rather hard to
implement.  In addition, calling git-blame with -C leads to similar
memory retention patterns.
---
 builtin/blame.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/builtin/blame.c b/builtin/blame.c
index 21f42b0..2596fbc 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1556,7 +1556,8 @@ finish:
 	}
 	for (i = 0; i < num_sg; i++) {
 		if (sg_origin[i]) {
-			drop_origin_blob(sg_origin[i]);
+			if (!sg_origin[i]->suspects)
+				drop_origin_blob(sg_origin[i]);
 			origin_decref(sg_origin[i]);
 		}
 	}

-- 
2.7.4