linux-kernel - Re: [PATCH v1] docs: describe how to quickly build Linux

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Date:   Thu, 2 Feb 2023 10:08:56 -0500
From:   Konstantin Ryabitsev <konstantin@...uxfoundation.org>
To:     Linux regressions mailing list <regressions@...ts.linux.dev>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v1] docs: describe how to quickly build Linux

On Thu, Feb 02, 2023 at 12:15:36PM +0100, Linux kernel regression tracking (Thorsten Leemhuis) wrote:
> Then I tried creating a shallow clone like this:
> 
> git clone
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> --depth 1 -b v6.1
> git remote set-branches --add origin master
> git fetch --all --shallow-exclude=v6.1
> git remote add -t linux-6.1.y linux-stable
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
> git fetch --all --shallow-exclude=v6.1
> 
> This took only roundabout 2 minutes and downloads & stores ~512 MByte
> data (without checkout).

Can we also include the option of just downloading the tarball, if it's a
released version? That's the fastest and most lightweight option 100% of the
time. :)

> Not totally sure, but the shallow clone somehow feels more appropriate
> for the use case (reminder, there is a "quickly" in the document title),
> even if such a clone is less flexible (e.g. users have to manually add
> stable branches they are interested it; and they need to be careful when
> using git fetch).
> 
> That's why I now strongly consider using the shallow clone method by
> default in v2 of this text. Or does that also create a lot of load on
> the servers? Or are there other strong reason why using a shallow clone
> might be a bad idea for this use case?

As I mentioned elsewhere, this is only a problem when it's done in batch mode
by CI systems. A full clone uses pregenerated pack files and is very cheap,
because it's effectively a sendfile operation. A shallow clone requires
generating a brand new pack, compressing it, and then keeping it around in
memory for the duration of the clone process. Not a big deal when a few humans
here and there do it, but when 50 CI nodes do it all at once, it effectively
becomes a DDoS. :)

-K