linux-kernel - Re: [PATCH v3 1/6] mm: add definition of PMD_PAGE

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Date:   Thu, 6 Aug 2020 13:11:12 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Idan Yaniv <idan.yaniv@....com>,
        Ingo Molnar <mingo@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org
Subject: Re: [PATCH v3 1/6] mm: add definition of PMD_PAGE_ORDER

On Tue, Aug 04, 2020 at 12:50:30PM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> The definition of PMD_PAGE_ORDER denoting the number of base pages in the
> second-level leaf page is already used by DAX and maybe handy in other
> cases as well.
> 
> Several architectures already have definition of PMD_ORDER as the size of
> second level page table, so to avoid conflict with these definitions use
> PMD_PAGE_ORDER name and update DAX respectively.
> 
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> ---
>  fs/dax.c                | 10 +++++-----
>  include/linux/pgtable.h |  3 +++
>  2 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 11b16729b86f..b91d8c8dda45 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -50,7 +50,7 @@ static inline unsigned int pe_order(enum page_entry_size pe_size)
>  #define PG_PMD_NR	(PMD_SIZE >> PAGE_SHIFT)
>  
>  /* The order of a PMD entry */
> -#define PMD_ORDER	(PMD_SHIFT - PAGE_SHIFT)
> +#define PMD_PAGE_ORDER	(PMD_SHIFT - PAGE_SHIFT)

Hm. Wouldn't it conflict with definition in pgtable.h? Or should we
include it instead?

> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 56c1e8eb7bb0..79f8443609e7 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -28,6 +28,9 @@
>  #define USER_PGTABLES_CEILING	0UL
>  #endif
>  
> +/* Number of base pages in a second level leaf page */
> +#define PMD_PAGE_ORDER	(PMD_SHIFT - PAGE_SHIFT)
> +
>  /*
>   * A page table page can be thought of an array like this: pXd_t[PTRS_PER_PxD]
>   *

-- 
 Kirill A. Shutemov