[RFC/PATCH] rename: warn user when we have turned off rename detection

[RFC/PATCH] rename: warn user when we have turned off rename detection

[Jeff King]

Signed-off-by: Jeff King <peff@peff.net>
---
This was another patch from late in the freeze period. It was in
response to a user getting confused about why rename detection wasn't
happening in a large merge. Is it appropriate to print this for every
rename we try? Or should it just be for merges?

Perhaps we should also bump the default limit from 100, which I think
was just arbitrarily chosen. I posted some numbers in:

  http://mid.gmane.org/20080211113516.GB6344@coredump.intra.peff.net

which imply that 200-400 is probably a more reasonable value. Thoughts?

 diffcore-rename.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 3d37725..31941bc 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -468,10 +468,11 @@ void diffcore_rename(struct diff_options *options)
 	 */
 	if (rename_limit <= 0 || rename_limit > 32767)
 		rename_limit = 32767;
-	if (num_create > rename_limit && num_src > rename_limit)
-		goto cleanup;
-	if (num_create * num_src > rename_limit * rename_limit)
+	if ((num_create > rename_limit && num_src > rename_limit) ||
+	    (num_create * num_src > rename_limit * rename_limit)) {
+		warning("too many files, skipping inexact rename detection");
 		goto cleanup;
+	}
 
 	mx = xmalloc(sizeof(*mx) * num_create * num_src);
 	for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
-- 
1.5.4.3.422.g55194

Re: [RFC/PATCH] rename: warn user when we have turned off rename detection

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> Signed-off-by: Jeff King <peff@peff.net>
> ---
> This was another patch from late in the freeze period. It was in
> response to a user getting confused about why rename detection wasn't
> happening in a large merge. Is it appropriate to print this for every
> rename we try? Or should it just be for merges?
>
> Perhaps we should also bump the default limit from 100, which I think
> was just arbitrarily chosen.
> ...
> +	if ((num_create > rename_limit && num_src > rename_limit) ||
> +	    (num_create * num_src > rename_limit * rename_limit)) {
> +		warning("too many files, skipping inexact rename detection");
>  		goto cleanup;
> +	}
> 
>  	mx = xmalloc(sizeof(*mx) * num_create * num_src);
>  	for (dst_cnt = i = 0; i < rename_dst_nr; i++) {

This reminds me of the 6d24ad9 (Optimize rename detection for a huge diff)
topic that reduces the above allocation greatly.  Some benching with the
patch may prove useful to establish much higher limits, I suspect.

Re: [RFC/PATCH] rename: warn user when we have turned off rename detection

[Jeff King]

On Fri, Feb 29, 2008 at 11:35:00PM -0800, Junio C Hamano wrote:

> > +	if ((num_create > rename_limit && num_src > rename_limit) ||
> > +	    (num_create * num_src > rename_limit * rename_limit)) {
> > +		warning("too many files, skipping inexact rename detection");
> >  		goto cleanup;
> > +	}
> > 
> >  	mx = xmalloc(sizeof(*mx) * num_create * num_src);
> >  	for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
> 
> This reminds me of the 6d24ad9 (Optimize rename detection for a huge diff)
> topic that reduces the above allocation greatly.  Some benching with the
> patch may prove useful to establish much higher limits, I suspect.

Actually, my timings are about the same. While the patch you mentioned
is nice for reducing the memory consumption, we still have an O(n^2)
loop.

-Peff

Re: [RFC/PATCH] rename: warn user when we have turned off rename detection

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

>> This reminds me of the 6d24ad9 (Optimize rename detection for a huge diff)
>> topic that reduces the above allocation greatly.  Some benching with the
>> patch may prove useful to establish much higher limits, I suspect.
>
> Actually, my timings are about the same. While the patch you mentioned
> is nice for reducing the memory consumption, we still have an O(n^2)
> loop.

Yeah, that one was not about the time but about the space, so it is
expected.