linux-kernel - Re: [PATCH 41/75] hexagon: Add pmd

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Message-ID: <YgAztSuYrKXZBgJx@casper.infradead.org>
Date:   Sun, 6 Feb 2022 20:46:45 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 41/75] hexagon: Add pmd_pfn()

On Sun, Feb 06, 2022 at 08:13:11PM +0200, Mike Rapoport wrote:
> On Fri, Feb 04, 2022 at 07:58:18PM +0000, Matthew Wilcox (Oracle) wrote:
> > I need to use this function in common code, so define it for hexagon.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > ---
> >  arch/hexagon/include/asm/pgtable.h | 3 ++-
> 
> Why hexagon out of all architectures?
> What about m68k, nios2, nds32 etc?

Presumably they don't support CONFIG_TRANSPARENT_HUGEPAGE.
This code isn't compiled when THP are disabled; at least I haven't
had a buildbot complaint for any other architectures.

> > +#define pmd_pfn(pmd)	(pmd_val(pmd) >> PAGE_SHIFT)
> 
> I'd put it in include/linux/pgtable.h inside #ifndef pmd_pfn

That's completely upside down.  pmd_pfn() should be defined by each
architecture (because generic code can't know anything about the format
of PMDs); if anything pmd_page() should be defined in linux/pgtable.h
in terms of pmd_pfn.

I'm not signing up to do that work as part of this series.  That seems
like a distraction.