Subject: Re: [PATCH 2/2] log: do not shorten decoration names too early

From: Jeff King <[email-masked]>
Date: Thu, 14 May 2015 18:33:13 -0400

On Thu, May 14, 2015 at 03:25:33PM -0700, Junio C Hamano wrote:

> @@ -90,6 +97,8 @@ static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s,	\
>  									\
>  	if (s->slab_count <= nth_slab) {				\
>  		int i;							\
> +		if (!add_if_missing)					\
> +			return NULL;					\
>  		s->slab = xrealloc(s->slab,				\
>  				   (nth_slab + 1) * sizeof(*s->slab));	\
>  		stat_ ##slabname## realloc++;				\

This skips extending the list of slabs if we would go past the nth slab.
But we don't fill in each slab in the first place. I.e., we may have 10
slabs, but only s->slab[10] is non-NULL.

A few lines below this, we xcalloc() it if necessary. I think that needs
to respect add_if_missing, as well.

>  void unuse_commit_buffer(const struct commit *commit, const void *buffer)
>  {
> -	struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
> -	if (v->buffer != buffer)
> +	struct commit_buffer *v = buffer_slab_peek(&buffer_slab, commit);
> +	if (v && v->buffer != buffer)
>  		free((void *)buffer);
>  }

I think you want:

  if (!v || v->buffer != buffer)

here. IOW, we free it only if it is not our cached buffer, and it cannot
be if we do not have a cached buffer. It may be easier to read by
flipping the logic:

  if (v && v->buffer == buffer)
	return; /* it is saved in the cache */
  free((void *)buffer);

Or some variation on that.

-Peff