linux-kernel - Re: [PATCH] Revert arm64: drop ranges in definition of ARCH_FORCE_MAX

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Message-ID: <86pm7ihl0i.wl-maz@kernel.org>
Date:   Tue, 02 May 2023 15:21:17 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Justin Forbes <jforbes@...oraproject.org>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Mike Rapoport <rppt@...nel.org>, Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        jmforbes@...uxtx.org, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Revert arm64: drop ranges in definition of ARCH_FORCE_MAX_ORDER

On Tue, 02 May 2023 15:07:41 +0100,
Catalin Marinas <catalin.marinas@....com> wrote:
> 
> On Mon, May 01, 2023 at 04:24:38PM -0500, Justin Forbes wrote:
> > On Sat, Apr 29, 2023 at 11:02 PM Mike Rapoport <rppt@...nel.org> wrote:
> > > Why the default MAX_ORDER was not acceptable on arm64 server machines but
> > > it is fine on, say, x86 and s390?
> > > I'm not asking how you made it possible in Fedora and RHEL, I'm asking why
> > > did you switch from the default order at all.
> > 
> > Because the MAX_ORDER on aarch64 with 4K pages is more tuned to the
> > needs of the average edge client, not so much those of a server class
> > machine.  And I get it, I would say well over 90% of the Fedora users
> > running aarch64 are indeed running on a rPi or similar with a small
> > memory footprint, and workloads which match that.  But we do support
> > and run a 4K page size aarch64 kernel on proper server class hardware,
> > running typical server workloads, and RHEL has a lot more users in the
> > server class than edge clients.   RHEL could probably default to 64K
> > pages, and most users would be happy with that. Fedora certainly could
> > not. 
> 
> I was talking to Marc Zyngier earlier and he reckons the need for a
> higher MAX_ORDER is the GIC driver ITS allocation for Thunder-X. I'm
> happy to make ARCH_MAX_ORDER higher in defconfig (12, 13?) if
> CONFIG_ARCH_THUNDER. Mobile vendors won't enable this platform.

In any case, I'd like to know exactly *what* requires it. The only
platform I know would benefit from this is the old TX1, but this
machine is more a boat anchor than a real server.

	M.

-- 
Without deviation from the norm, progress is not possible.