Re: [PATCH] submodule: use cheaper check for submodule pushes
- Date: Thu, 13 Jul 2017 13:54:04 -0700
- From: Stefan Beller <sbeller@xxxxxxxxxx>
- Subject: Re: [PATCH] submodule: use cheaper check for submodule pushes
On Thu, Jul 13, 2017 at 1:48 PM, Jonathan Nieder <jrnieder@xxxxxxxxx> wrote:
> Stefan Beller wrote:
>> Yes we are safe, because the function itself only spawns a child process
>> (not using any of the objects).
>> It's only caller push_unpushed_submodules also doesn't rely on objects
>> loaded after calling push_submodule.
>> The caller of push_unpushed_submodules (transport.c, transport_push)
>> also doesn't need submodule objects loaded.
> Thanks for looking into it. This is what the commit message should
> say to help reviewers or people trying to understand it later. The
> footnotes don't help and are distracting, except that it makes sense
> to point out the original GSoC patch to say the alternate submodule
> odb wasn't needed even then.
> Subject: push: do not add submodule odb as an alternate when recursing on demand
> "git push --recurse-submodules=on-demand" adds each submodule as an
> alternate with add_submodule_odb before checking whether the
> submodule has anything to push and pushing it if so.
> However, it never accesses any objects from the submodule. In the
> parent process it uses the submodule's ref database to see if there
> is anything to push. The actual push (which does rely on objects)
> occurs in a child process.
> The same was try when this call was originally added in
> v1.7.11-rc0~111^2 (push: teach --recurse-submodules the on-demand
> option, 2012-03-29). Most likely it was added by analogy with
> fetch --recurse-submodules=on-demand, which did use the submodule's
> object database.
> Use is_submodule_populated_gently instead, which is simpler and
Thanks for giving a good example of commit message that I could use
in a reroll.
> With such a commit message change, this seems like a reasonable change
> in principle (though I haven't looked carefully to verify it).
> My one doubt is the is_submodule_populated_gently. Why are we using
> that instead of simpler is_submodule_populated? The names and API
> comments don't explain.
One could posit this is laziness of thinking.
See 15cdc64776 (make is_submodule_populated gently, 2017-03-14),
and discover there is no non-gentle version of is_submodule_populated.
And for each new use, it may be cheaper to just use the gentle version
instead of adding a non-gentle version.