Subject: Re: [PATCH v6 06/26] mm: Add PG_arch_2 page flag

From: Catalin Marinas <[email-masked]>
Date: Mon, 6 Jul 2020 12:21:13 +0100

On Mon, Jul 06, 2020 at 10:24:04AM +0200, David Hildenbrand wrote:
> On 03.07.20 17:36, Catalin Marinas wrote:
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index 6be1aa559b1e..276140c94f4a 100644
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> > @@ -135,6 +135,9 @@ enum pageflags {
> >  #if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
> >  	PG_young,
> >  	PG_idle,
> > +#endif
> > +#ifdef CONFIG_64BIT
> > +	PG_arch_2,
> >  #endif
> >  	__NR_PAGEFLAGS,
> 
> People are usually *very* picky when it comes to new page flags. It
> somewhat concerns me that we bump up __NR_PAGEFLAGS for any 64bit arch.
> That feels wrong.

It was guarded by a specific config option initially but the comments
suggested that it could be dropped for 64-bit architectures:

https://lore.kernel.org/linux-arm-kernel/[email-masked]/

The page flags is indeed a pretty limited resource as it also includes
the sparsemem section, node and zone fields. However, on 64-bit this
should be fine (the sparsemem section is gone with vmemmap support).

-- 
Catalin

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