linux-kernel - Re: [GIT PULL] dma-mapping updates for Linux 6.6

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Date:   Tue, 29 Aug 2023 20:54:43 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
        Petr Tesarik <petr.tesarik.ext@...wei.com>
Subject: Re: [GIT PULL] dma-mapping updates for Linux 6.6

On Tue, 29 Aug 2023 at 08:23, Christoph Hellwig <hch@...radead.org> wrote:=
>
> Yajun Deng (2):
>       dma-contiguous: support per-numa CMA for all architectures

What?

This commit seems entirely bogus and is actively misleading.

It claims to enable support for per-numa CMA for all architectures.

It does no such thing.

All it does is to change the default value for a config option. It was
perfectly available before, now it is - incorrectly - made 'default y'
in case the config supports NUME at all.

There seems to be no real reason to change the default value of this
config option. The commit message most definitely doesn't argue for
it, since it talks about something entirely different than what the
code changes does.

I have taken this, but I protest these kinds of nonsensical changes.
That commit is actively misleading and confused, and I think the
default value for that config option should just be 'n' on all
architectures.

Why is this option so important that it should be enabled just because
some minimal NUMA support might be enabled?

Please don't add these kinds of hidden "default y" by making them
default on some much more common option instead.

                Linus