Re: port-i386/57641: -current/i386 no longer installs in 32 MB

[Andrew Doran <ad%netbsd.org@localhost>]

The following reply was made to PR port-i386/57641; it has been noted by GNATS.

From: Andrew Doran <ad%netbsd.org@localhost>
To: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Cc: gnats-bugs%netbsd.org@localhost, port-i386-maintainer%netbsd.org@localhost,
	gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost,
	Andreas Gustafsson <gson%gson.org@localhost>
Subject: Re: port-i386/57641: -current/i386 no longer installs in 32 MB
Date: Fri, 6 Oct 2023 22:26:06 +0000

 On Wed, Oct 04, 2023 at 10:50:25PM +0000, Taylor R Campbell wrote:
 
 > > From: Andrew Doran <ad%netbsd.org@localhost>
 > > 
 > > It's probably not an satisfying answer but I don't think it's a valid test
 > > because DIAGNOSTIC uses a lot more memory and we shouldn't be shipping
 > > actual release kernels with it enabled.
 > 
 > How much more memory?  DIAGNOSTIC is supposed to be reasonably cheap,
 > mostly cheap predicted-not-taken branches in assertions.
 
 There's not an easy formula for that.  kmem adds sizeof(size_t) to every
 allocation to track that size allocated is the same as size freed, which
 eats a lot more space than expected because alignment requirements (for
 cache friendliness) still need to be met.
 
 > Should we move more things to DEBUG instead for expensive checks and
 > higher memory usage?
 
 Yeah I think so.  I'll cover it with DEBUG in a week or so if nobody has a
 serious objection.
 
 > > Looking back over the history for the amd64 GENERIC kernel it seems like
 > > nobody has disabled it for any release since NetBSD 5 though which sucks.
 > 
 > What history did you check?  It has always been disabled in every
 > release branch.  See, e.g., this commit on the netbsd-9 branch:
 > 
 > http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/amd64/conf/GENERIC?rev=1.531.2.4&content-type=text/x-cvsweb-markup&only_with_tag=netbsd-9
 
 I looked at the history for amd64 GENERIC on cvsweb.netbsd.org, searched for
 DIAGNOSTIC and it didn't find anything like that.  Maybe the page hadn't
 finished loading or something.  I also had a hazy memory of installing a
 release years ago and being sure it had DIAGNOSTIC enabled.  In any case it
 seems I was wrong, cheers.
 
 Andrew