Re: [PATCH 1/1] fetch: set size_multiple in split_commit_graph_opts

> From: Derrick Stolee <dstolee@microsoft.com>
> 
> In 50f26bd ("fetch: add fetch.writeCommitGraph config setting",
> 2019-09-02), the fetch builtin added the capability to write a
> commit-graph using the "--split" feature. This feature creates
> multiple commit-graph files, and those can merge based on a set
> of "split options" including a size multiple. The default size
> multiple is 2, which intends to provide a log_2 N depth of the
> commit-graph chain where N is the number of commits.
> 
> However, I noticed during dogfooding that my commit-graph chains
> were becoming quite large when left only to builds by 'git fetch'.
> It turns out that in split_graph_merge_strategy(), we default the
> size_mult variable to 2 except we override it with the context's
> split_opts if they exist. In builtin/fetch.c, we create such a
> split_opts, but do not populate it with values.
> 
> This problem is due to two failures:
> 
>  1. It is unclear that we can add the flag COMMIT_GRAPH_WRITE_SPLIT
>     with a NULL split_opts.
>  2. If we have a non-NULL split_opts, then we override the default
>     values even if a zero value is given.
> 
> Correct both of these issues. First, do not override size_mult when
> the options provide a zero value. Second, stop creating a split_opts
> in the fetch builtin.