linux-kernel - Re: [PATCH V2] arm64/mm: Drop <asm/page-def.h>

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Message-ID: <YS9/7mE+5uieqKh8@arm.com>
Date:   Wed, 1 Sep 2021 14:28:14 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH V2] arm64/mm: Drop <asm/page-def.h>

On Tue, Aug 31, 2021 at 09:15:30AM +0530, Anshuman Khandual wrote:
> On 8/21/21 12:05 AM, Catalin Marinas wrote:
> > On Fri, Aug 20, 2021 at 04:35:16PM +0530, Anshuman Khandual wrote:
> >> PAGE_SHIFT (PAGE_SIZE and PAGE_MASK) which is derived from ARM64_PAGE_SHIFT
> >> should be moved into <asm/page.h> instead like in case for other platforms,
> >> and then subsequently <asm/page-def.h> can be just dropped off completely.
> > 
> > These were moved to page-def.h as part of commit b6531456ba27 ("arm64:
> > factor out PAGE_* and CONT_* definitions") to avoid some circular header
> > dependencies.
> > 
> >> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> >> index 824a3655dd93..649d26396f9e 100644
> >> --- a/arch/arm64/include/asm/memory.h
> >> +++ b/arch/arm64/include/asm/memory.h
> >> @@ -12,7 +12,7 @@
> >>  
> >>  #include <linux/const.h>
> >>  #include <linux/sizes.h>
> >> -#include <asm/page-def.h>
> >> +#include <asm/page.h>
> > 
> > In 5.14-rc3, asm/page.h still includes asm/memory.h.
> 
> Dropping <asm/memory.h> from <asm/page.h> does not seem to cause
> any problem, will change that. Afterwards build tested it across
> page sizes and also with some random configs. Is that circular
> dependency still present ? Also wondering why was <asm/memory.h>
> included in <asm/page.h> to begin with ?

asm/memory.h is not included by any of the generic files, however it has
essential definitions like PAGE_OFFSET, THREAD_SIZE. The expectations
from the arch code is to have these defined in asm/page.h (see the
asm-generic/page.h), hence the inclusion. It probably gets included by
other arch headers and that's why you don't get any errors, but I
wouldn't rely on this.

I don't remember how we ended up with a separate memory.h file. On arm64
we inherited it from arch/arm.

-- 
Catalin