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Re: [PATCH] submodule: use cheaper check for submodule pushes




On Thu, Jul 13, 2017 at 1:48 PM, Jonathan Nieder <jrnieder@xxxxxxxxx> wrote:
> Hi,
>
> 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.
>
> E.g.:
>
>  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
>  cheaper.

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.

Thanks,
Stefan