Re: [PATCH v4 3/3] regex: use regexec_buf()

> On Wed, Sep 21, 2016 at 08:24:14PM +0200, Johannes Schindelin wrote:
> 
> > The new regexec_buf() function operates on buffers with an explicitly
> > specified length, rather than NUL-terminated strings.
> > 
> > We need to use this function whenever the buffer we want to pass to
> > regexec() may have been mmap()ed (and is hence not NUL-terminated).
> > 
> > Note: the original motivation for this patch was to fix a bug where
> > `git diff -G <regex>` would crash. This patch converts more callers,
> > though, some of which explicitly allocated and constructed
> > NUL-terminated strings (or worse: modified read-only buffers to insert
> > NULs).
> 
> Nice. I probably would have split these into their own patch, but I
> think it is OK here.

> > @@ -228,18 +227,16 @@ static long ff_regexp(const char *line, long len,
> >  			len--;
> >  	}
> >  
> > -	line_buffer = xstrndup(line, len); /* make NUL terminated */
> > -
> 
> Nice to see this one going away in particular, since it's called quite a
> lot. According to perf, "git log -p" on git.git drops about 1.5 million
> malloc calls (about 9% of the total). And here are best-of-five results
> for that same command:
> 
>   [before]
>   real    0m14.676s
>   user    0m13.988s
>   sys     0m0.676s
> 
>   [after]
>   real    0m14.394s
>   user    0m13.624s
>   sys     0m0.760s
> 
> Not a _huge_ improvement, but more significant than the run-to-run
> noise.