Re: [PATCH] arm64: Make the ARCH_FORCE_MAX_ORDER config input prompt unconditional

From: Mike Rapoport <rppt@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Justin Forbes <jforbes@fedoraproject.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] arm64: Make the ARCH_FORCE_MAX_ORDER config input prompt unconditional
Date: Fri, 5 May 2023 15:00:57 -0700	[thread overview]
Message-ID: <ZFV8mZwCFzW9ubX9@kernel.org> (raw)
In-Reply-To: <CAMj1kXFi+bXJUN8tZtW-kfGrmKDC_C6u9NpWXyWMnbpeKWHX-A@mail.gmail.com>

On Wed, May 03, 2023 at 05:41:19PM +0200, Ard Biesheuvel wrote:
> On Wed, 3 May 2023 at 17:36, Justin Forbes <jforbes@fedoraproject.org> wrote:
> >
> > On Wed, May 3, 2023 at 7:33 AM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > >
> > > Commit 34affcd7577a ("arm64: drop ranges in definition of
> > > ARCH_FORCE_MAX_ORDER") dropped the ranges from the config entry and
> > > introduced an EXPERT condition on the input prompt instead. This change
> > > may affect some distro kernels that change ARCH_FORCE_MAX_ORDER but do
> > > not want to enable EXPERT.
> > >
> > > Drop EXPERT from the input prompt together with the (ARM64_4K_PAGES ||
> > > ARM64_16K_PAGES) condition as the latter no longer makes sense after the
> > > ranges were removed. The latter makes all the page size configurations
> > > consistent w.r.t. ARCH_FORCE_MAX_ORDER.
> > >
> > > Fixes: 34affcd7577a ("arm64: drop ranges in definition of ARCH_FORCE_MAX_ORDER")
> > > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > > Reported-by: Justin M. Forbes <jforbes@fedoraproject.org>
> > > Cc: Will Deacon <will@kernel.org>
> > > Cc: Mike Rapoport <rppt@kernel.org>
> > > Cc: Andrew Morton <akpm@linux-foundation.org>
> >
> > This works for me, thanks.
> >
> > Acked-by: Justin M. Forbes <jforbes@fedoraproject.org>
> >
> 
> I'd still be interested in gaining a better understanding as to why
> Fedora/RHEL think they need to change this value on arm64. In
> particular, whether it is to support ThunderX, or whether there are
> any good reasons for doing so that we are unaware of.

Yeah, there still was no explanation why Fedora/RHEL had to increase
MAX_ORDER in their configs.

I'm surely missing something, but I also don't understand why ThunderX
would need physically contiguous allocations larger than 4M.

-- 
Sincerely yours,
Mike.

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