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MagaTailor opened this issue Nov 29, 2015 · 3 comments
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Redundant cloning of git submodules #30107

MagaTailor opened this issue Nov 29, 2015 · 3 comments

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@MagaTailor
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When building from git source, the build system makes a deep clone of git submodules, even those, like jemalloc or llvm, that had been disabled with configure options. (--disable-jemalloc and --llvm-root respectively)

Not downloading a couple hundred megabytes of data spread over tens of thousands of small files is especially important on flash devices (and slow connections).
@Aatch
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Aatch commented Nov 30, 2015

At the very least it should probably do a shallower clone of those repos. As best I can tell, you should be able to just pass --depth 1 to git submodule update just fine.

@MagaTailor
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Yep, that would be a great start. However the gist of this report is to completely forego downloading the source trees that are never going to be used.

@MagaTailor MagaTailor mentioned this issue Jan 2, 2016
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@srawlins srawlins mentioned this issue Jun 11, 2016
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japaric pushed a commit to japaric/rust that referenced this issue Aug 28, 2016
rustbuild: smarter git submodule-ing
a375799 
With this commit, if one bootstraps rust against system llvm then the
src/llvm submodule is not updated/checked-out. This saves considerable
network bandwith when starting from a fresh clone of rust-lang/rust as
the llvm submodule is never cloned.

cc rust-lang#30107
@japaric japaric mentioned this issue Aug 28, 2016
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bors added a commit that referenced this issue Aug 29, 2016
@bors
Auto merge of #36062 - japaric:smarter-submodules, r=alexcrichton
86dde9b 
rustbuild: smarter `git submodule`-ing

With this commit, if one bootstraps rust against system llvm then the
src/llvm submodule is not updated/checked-out. This saves considerable
network bandwith when starting from a fresh clone of rust-lang/rust as
the llvm submodule is never cloned.

cc #30107

r? @alexcrichton
cc @petevine

~~We could also avoid updating the jemalloc submodule if --disable-jemalloc is used. It just hasn't been implemented.~~ Done

This probably doesn't handle "recursive" submodules correctly but I think we don't have any of those right now.

I'm still testing a bootstrap but already confirmed that the llvm submodule doesn't get updated when `--llvm-root` is passed to `configure`.
@MagaTailor
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@japaric I've just tested your patch, having done a rust shallow clone first and llvm is not cloned at all but jemalloc still is. Still, a huge improvement; thanks!

I also paid attention to the amount of data downloaded by fully cloning other modules, like compiler-rt, liblibc, etc. and it seems bootstrapping from a source snapshot is still the fastest option, requiring a 50% smaller download.

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@steveklabnik @Aatch @MagaTailor