linux-kernel - Re: [PATCH v3 5/5] mm: page_alloc: reduce unnecessary binary search in early_pfn

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Date:   Tue, 27 Mar 2018 19:51:56 +0200
From:   Daniel Vacek <neelx@...hat.com>
To:     Jia He <hejianet@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mel Gorman <mgorman@...e.de>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Gioh Kim <gi-oh.kim@...fitbricks.com>,
        Steven Sistare <steven.sistare@...cle.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        open list <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        James Morse <james.morse@....com>,
        Steve Capper <steve.capper@....com>, x86@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Kemi Wang <kemi.wang@...el.com>,
        Petr Tesarik <ptesarik@...e.com>,
        YASUAKI ISHIMATSU <yasu.isimatu@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Nikolay Borisov <nborisov@...e.com>,
        Jia He <jia.he@...-semitech.com>
Subject: Re: [PATCH v3 5/5] mm: page_alloc: reduce unnecessary binary search
 in early_pfn_valid()

On Mon, Mar 26, 2018 at 5:02 AM, Jia He <hejianet@...il.com> wrote:
> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
> where possible") optimized the loop in memmap_init_zone(). But there is
> still some room for improvement. E.g. in early_pfn_valid(), if pfn and
> pfn+1 are in the same memblock region, we can record the last returned
> memblock region index and check check pfn++ is still in the same region.
>
> Currently it only improve the performance on arm64 and will have no
> impact on other arches.
>
> Signed-off-by: Jia He <jia.he@...-semitech.com>
> ---
>  arch/x86/include/asm/mmzone_32.h |  2 +-
>  include/linux/mmzone.h           | 12 +++++++++---
>  mm/page_alloc.c                  |  2 +-
>  3 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/mmzone_32.h b/arch/x86/include/asm/mmzone_32.h
> index 73d8dd1..329d3ba 100644
> --- a/arch/x86/include/asm/mmzone_32.h
> +++ b/arch/x86/include/asm/mmzone_32.h
> @@ -49,7 +49,7 @@ static inline int pfn_valid(int pfn)
>         return 0;
>  }
>
> -#define early_pfn_valid(pfn)   pfn_valid((pfn))
> +#define early_pfn_valid(pfn, last_region_idx)  pfn_valid((pfn))
>
>  #endif /* CONFIG_DISCONTIGMEM */
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index d797716..3a686af 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1267,9 +1267,15 @@ static inline int pfn_present(unsigned long pfn)
>  })
>  #else
>  #define pfn_to_nid(pfn)                (0)
> -#endif
> +#endif /*CONFIG_NUMA*/
> +
> +#ifdef CONFIG_HAVE_ARCH_PFN_VALID
> +#define early_pfn_valid(pfn, last_region_idx) \
> +                               pfn_valid_region(pfn, last_region_idx)
> +#else
> +#define early_pfn_valid(pfn, last_region_idx)  pfn_valid(pfn)
> +#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
>
> -#define early_pfn_valid(pfn)   pfn_valid(pfn)
>  void sparse_init(void);
>  #else
>  #define sparse_init()  do {} while (0)
> @@ -1288,7 +1294,7 @@ struct mminit_pfnnid_cache {
>  };
>
>  #ifndef early_pfn_valid
> -#define early_pfn_valid(pfn)   (1)
> +#define early_pfn_valid(pfn, last_region_idx)  (1)
>  #endif
>
>  void memory_present(int nid, unsigned long start, unsigned long end);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0bb0274..debccf3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5484,7 +5484,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>                 if (context != MEMMAP_EARLY)
>                         goto not_early;
>
> -               if (!early_pfn_valid(pfn)) {
> +               if (!early_pfn_valid(pfn, &idx)) {
>  #if (defined CONFIG_HAVE_MEMBLOCK) && (defined CONFIG_HAVE_ARCH_PFN_VALID)
>                         /*
>                          * Skip to the pfn preceding the next valid one (or
> --
> 2.7.4
>

Hmm, what about making index global variable instead of changing all
the prototypes? Similar to early_pfnnid_cache for example. Something
like:

#ifdef CONFIG_HAVE_ARCH_PFN_VALID
extern int early_region_idx __meminitdata;
#define early_pfn_valid(pfn) \
                               pfn_valid_region(pfn, &early_region_idx)
#else
#define early_pfn_valid(pfn)  pfn_valid(pfn)
#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/

And move this to arch/arm64/include/asm/page.h ?

--nX