builtin_diff calls fill_mmfile fairly early, which in turn
calls diff_populate_filespec, which actually retrieves the
file's blob contents into a buffer. Long ago, this was
sensible as we would need to look at the blobs eventually.
These days, however, we may not ever want those blobs if we
end up using a textconv cache, and for large binary files
(exactly the sort for which you might have a textconv
cache), just retrieving the objects can be costly.
This patch just pushes the fill_mmfile call a bit later, so
we can avoid populating the filespec in some cases. There
is one thing to note that looks like a bug but isn't. We
push the fill_mmfile down into the first branch of a
conditional. It seems like we would need it on the other
branch, too, but we don't; fill_textconv does it for us (in
fact, before this, we were just writing over the results of
the fill_mmfile on that branch).
Here's a timing sample on a commit with 45 changed jpgs and
avis. The result is fully textconv cached, but we still
wasted a lot of time just pulling the blobs from storage.
The total size of the blobs (source and dest) is about
180M.
[before]
$ time git show >/dev/null
real 0m0.352s
user 0m0.148s
sys 0m0.200s
[after]
$ time git show >/dev/null
real 0m0.009s
user 0m0.004s
sys 0m0.004s
And that's on a warm cache. On a cold cache, the "after"
case is not much worse, but the "before" case has to do an
extra 180M of I/O.
Signed-off-by: Jeff King <peff@xxxxxxxx>
---
I remember when I first started using git having it go so fast that I
had to double-check that it had actually worked correctly. I had another
of those moments when I ran this. But it correctly processed everything
I threw at it. More stress-testing appreciated. :)
diff.c | 9 ++++-----
1 files changed, 4 insertions(+), 5 deletions(-)
diff --git a/diff.c b/diff.c
index 72d8503..4cb6d9a 100644
--- a/diff.c
+++ b/diff.c
@@ -1680,12 +1680,11 @@ static void builtin_diff(const char *name_a,
}
}
- if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0)
- die("unable to read files to diff");
-
if (!DIFF_OPT_TST(o, TEXT) &&
- ( (diff_filespec_is_binary(one) && !textconv_one) ||
- (diff_filespec_is_binary(two) && !textconv_two) )) {
+ ( (!textconv_one && diff_filespec_is_binary(one)) ||
+ (!textconv_two && diff_filespec_is_binary(two)) )) {
+ if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0)
+ die("unable to read files to diff");
/* Quite common confusing case */
if (mf1.size == mf2.size &&
!memcmp(mf1.ptr, mf2.ptr, mf1.size))
--
1.7.0.4.299.gba9d4
--
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