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From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>
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	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH V8] mm/debug: Add tests validating architecture page table helpers
Date: Wed, 6 Nov 2019 18:07:44 +0000	[thread overview]
Message-ID: <b93ffe1f-b198-a042-ecd4-b0f2b0171f72@synopsys.com> (raw)
In-Reply-To: <dc2746c9-bde4-ac00-88d1-2bd1cea1f105@arm.com>

On 11/5/19 7:03 PM, Anshuman Khandual wrote:
> But should not pfn_pmd() be encapsulated inside HAVE_ARCH_TRANSPARENT_HUGEPAGE
> at the minimum (but I would say it should be available always, nonetheless) when
> the platform subscribes to THP irrespective of whether THP is enabled or not.

For ARC it was only introduced/needed when I added THP support so it is dependent
in some way.

> I could see in the file (arch/arc/include/asm/pgtable.h) that fetching pfn_pmd()
> and all other basic PMD definitions is conditional on CONFIG_TRANSPARENT_HUGEPAGE.
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> #include <asm/hugepage.h>
> #endif
>
> IIUC, CONFIG_TRANSPARENT_HUGEPAGE should only encapsulate PMD page table helpers
> which are expected from generic THP code (pmd_trans_huge, pmdp_set_access_flags
> etc) but not the basic PMD helpers like pmd_pfn, pmd_mkyoung, pmd_mkdirty,
> pmd_mkclean etc. 

ARC only has 2 levels of paging, so these don't make any sense in general and
needed only for THP case.
I case of arch/arm you see it is only defined in pgtable-3level.h

> Hence wondering will it be possible to accommodate following
> code change on arc platform (not even compiled) in order to fix the problem ?

I'm open to making changes in ARC code but lets do the right thing.

>   */
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE
>  #include <asm/hugepage.h>
>  #endif

This in wrong.  CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE is a just a glue toggle,
used only in Kconfig files (and not in any "C" code).  It enables generic Kconfig
code to allow visibility of CONFIG_TRANSPARENT_HUGEPAGE w/o every arch needing to
do a me too.

I think you need to use CONFIG_TRANSPARENT_HUGEPAGE to guard appropriate tests. I
understand that it only

-Vineet


  reply	other threads:[~2019-11-06 18:20 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-28  5:29 [PATCH V8] mm/debug: Add tests validating architecture page table helpers Anshuman Khandual
2019-10-29 10:31 ` Qian Cai
2019-11-04  2:15   ` Anshuman Khandual
2019-11-05  0:00 ` Anshuman Khandual
2019-11-05 22:30   ` Vineet Gupta
2019-11-06  3:03     ` Anshuman Khandual
2019-11-06 18:07       ` Vineet Gupta [this message]
2019-11-07  4:44         ` Anshuman Khandual
2019-11-07 19:05           ` Vineet Gupta
2019-11-08  4:27             ` Anshuman Khandual
2019-11-11 19:06               ` Vineet Gupta
2019-11-05  0:30 ` Anshuman Khandual
2019-11-05 19:36 ` Gerald Schaefer
2019-11-06  3:10   ` Anshuman Khandual
2019-11-06  3:22 ` Anshuman Khandual
2019-11-06  6:41   ` Christophe Leroy
2019-11-06  7:34     ` Anshuman Khandual
2019-11-07 12:54       ` Michael Ellerman
2019-11-07 13:22         ` Anshuman Khandual

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