[bug#57788] [PATCH] gnu: rust: Disable debug info to reduce build requirements

[Mark H Weaver <mhw@netris.org>]

Hi Efraim,

Efraim Flashner <efraim@flashner.co.il> writes:

> On Tue, Sep 13, 2022 at 07:56:46PM -0400, Mark H Weaver wrote:
>> The following patch, which I've tested only on my private branch of
>> Guix, dramatically reduces the amount of memory and time required to
>> build Rust.
>> 
>> With this patch applied, I'm able to build Rust on a Thinkpad X200 with
>> only 4 GB of RAM using both cores.  Without it, I'm unable to build Rust
>> at all, even with parallel builds disabled, running in a bare text-only
>> terminal, and with every nonessential daemon stopped.  When I tried, a
>> single compiler process used more than 9 GB of virtual memory with heavy
>> thrashing before the OOM killer finally put it out of its misery.
>
> Your x200 is an x86_64?

Yes, with only 4 GB of RAM.

> How much RAM+swap did you end up using with this patch?

During the times when I was monitoring it, the build process with
parallel build enabled (2 parallel jobs) fit entirely within my 4 GB of
RAM, while also running a modest X session with Emacs.

>> Moreover, with this patch the builds are dramatically faster than I've
>> previously observed.  In my earlier bootstraps of Rust (up to
>> rust-1.51), it took about 5 hours to build each compiler on my machine.
>> Now it takes only about 2 hours per compiler, except for the initial
>> bootstrap (1.54) which takes about 4 hours.
>
> I tested it out on my machine, it brought the build time down from 101
> minutes to 71 minutes. Not the same improvement, but still noticeable.

I'm glad to hear it!  I guess the improvement was more dramatic on my
system because it was previously thrashing (lots of swapping due to
insufficient RAM), whereas your system probably has enough RAM :-)

>> The following patch is meant to be applied to the 'staging' branch, but
>> I've only tested it on my own private branch, which is based on very old
>> 'master' (April 2021) and is thus quite different by now.
>> 
>> I offer it here in case it might be of interest, although it hasn't been
>> tested on contemporary Guix.  I'm not subscribed to this mailing list,
>> so please make sure to CC me on any replies you'd like me to see.
>> 
>>      Regards,
>>        Mark
>
> I'm building out to librsvg on staging right now with this patch
> applied, so hopefully we'll see that it's good.
>
> I'm assuming that setting CARGO_PROFILE_DEV_DEBUG to false won't cause
> any problems.

After writing my previous message, I ended up adding another hunk to my
patch, to disable debugging in the final 'rust' compiler:

--8<---------------cut here---------------start------------->8---
diff --git a/gnu/packages/rust.scm b/gnu/packages/rust.scm
index 25295a283e..cf2c66f334 100644
--- a/gnu/packages/rust.scm
+++ b/gnu/packages/rust.scm
@@ -704,6 +704,13 @@ (define-public rust
                      (("^python =.*" all)
                       (string-append all
                                      "gdb = \"" gdb "/bin/gdb\"\n"))))))
+             (add-before 'build 'disable-debug
+               (lambda _
+                 ;; reduce memory requirements during the build
+                 (setenv "CARGO_PROFILE_DEV_DEBUG" "false")
+                 (substitute* "config.toml"
+                   (("\\[rust\\].*" all)
+                    (string-append all "debug = false\n")))))
              (replace 'build
                ;; Phase overridden to also build rustfmt.
                (lambda* (#:key parallel-build? #:allow-other-keys)
--8<---------------cut here---------------end--------------->8---

In retrospect, for the post-mrustc compilers, it might have been
sufficient to add "debug = false" to the [rust] section of config.toml
in the 'rust-1.55' variable.  This might also eliminate the need to set
CARGO_PROFILE_DEV_DEBUG.  However, I haven't tried it.

Thanks for working on it, Efraim!

      Regards,
        Mark

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