linux-kernel - Re: [PATCH 02/14] arm64: drop ranges in definition of ARCH_FORCE_MAX

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Date:   Thu, 23 Mar 2023 12:37:05 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "David S. Miller" <davem@...emloft.net>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Guo Ren <guoren@...nel.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Rich Felker <dalias@...c.org>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Zi Yan <ziy@...dia.com>, linux-arm-kernel@...ts.infradead.org,
        linux-csky@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mm@...ck.org, linux-sh@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, linuxppc-dev@...ts.ozlabs.org,
        sparclinux@...r.kernel.org
Subject: Re: [PATCH 02/14] arm64: drop ranges in definition of
 ARCH_FORCE_MAX_ORDER

On Thu, Mar 23, 2023 at 10:15:33AM +0000, Catalin Marinas wrote:
> On Thu, Mar 23, 2023 at 11:21:44AM +0200, Mike Rapoport wrote:
> > From: "Mike Rapoport (IBM)" <rppt@...nel.org>
> > 
> > It is not a good idea to change fundamental parameters of core memory
> > management. Having predefined ranges suggests that the values within
> > those ranges are sensible, but one has to *really* understand
> > implications of changing MAX_ORDER before actually amending it and
> > ranges don't help here.
> > 
> > Drop ranges in definition of ARCH_FORCE_MAX_ORDER
> > 
> > Signed-off-by: Mike Rapoport (IBM) <rppt@...nel.org>
> > ---
> >  arch/arm64/Kconfig | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index e60baf7859d1..bab6483e4317 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -1489,9 +1489,7 @@ config XEN
> >  config ARCH_FORCE_MAX_ORDER
> >  	int "Maximum zone order" if ARM64_4K_PAGES || ARM64_16K_PAGES
> >  	default "13" if ARM64_64K_PAGES
> > -	range 11 13 if ARM64_16K_PAGES
> >  	default "11" if ARM64_16K_PAGES
> > -	range 10 15 if ARM64_4K_PAGES
> >  	default "10"
> 
> I don't mind rewriting the help text as in the subsequent patch but I'd
> keep the ranges as a safety measure. It's less wasted time explaining to
> people why some random max order doesn't work. Alternatively, we can
> drop the ranges but make this option configurable only if EXPERT.

I like the EXPERT alternative more. I'll add it in v2.
 
> -- 
> Catalin

-- 
Sincerely yours,
Mike.