linux-kernel - Re: [PATCH v9 0/6] optimize memblock_next_valid_pfn and early_pfn

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Message-ID: <20180702114037.GJ19043@dhcp22.suse.cz>
Date:   Mon, 2 Jul 2018 13:40:37 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Jia He <hejianet@...il.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mel Gorman <mgorman@...e.de>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....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>,
        Daniel Vacek <neelx@...hat.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, James Morse <james.morse@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Steve Capper <steve.capper@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        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>, richard.weiyang@...il.com
Subject: Re: [PATCH v9 0/6] optimize memblock_next_valid_pfn and
 early_pfn_valid on arm and arm64

On Fri 29-06-18 10:29:17, Jia He wrote:
> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
> where possible") tried to optimize the loop in memmap_init_zone(). But
> there is still some room for improvement.

It would be great to shortly describe those optimization from high level
POV.

> 
> Patch 1 introduce new config to make codes more generic
> Patch 2 remain the memblock_next_valid_pfn on arm and arm64
> Patch 3 optimizes the memblock_next_valid_pfn()
> Patch 4~6 optimizes the early_pfn_valid()
> 
> As for the performance improvement, after this set, I can see the time
> overhead of memmap_init() is reduced from 27956us to 13537us in my
> armv8a server(QDF2400 with 96G memory, pagesize 64k).

So this is 13ms saving when booting 96G machine. Is this really worth
the additional code? Are there any other benefits?
[...]
>  arch/arm/Kconfig          |  4 +++
>  arch/arm/mm/init.c        |  1 +
>  arch/arm64/Kconfig        |  4 +++
>  arch/arm64/mm/init.c      |  1 +
>  include/linux/early_pfn.h | 79 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/memblock.h  |  2 ++
>  include/linux/mmzone.h    | 18 ++++++++++-
>  mm/Kconfig                |  3 ++
>  mm/memblock.c             |  9 ++++++
>  mm/page_alloc.c           |  5 ++-
>  10 files changed, 124 insertions(+), 2 deletions(-)
>  create mode 100644 include/linux/early_pfn.h

-- 
Michal Hocko
SUSE Labs