Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 2 Jul 2018 13:40:37 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Jia He <hejianet@gmail.com>
Cc:     Russell King <linux@armlinux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mel Gorman <mgorman@suse.de>,
        Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Pavel Tatashin <pasha.tatashin@oracle.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        AKASHI Takahiro <takahiro.akashi@linaro.org>,
        Gioh Kim <gi-oh.kim@profitbricks.com>,
        Steven Sistare <steven.sistare@oracle.com>,
        Daniel Vacek <neelx@redhat.com>,
        Eugeniu Rosca <erosca@de.adit-jv.com>,
        Vlastimil Babka <vbabka@suse.cz>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, James Morse <james.morse@arm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Steve Capper <steve.capper@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Philippe Ombredanne <pombredanne@nexb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Kemi Wang <kemi.wang@intel.com>,
        Petr Tesarik <ptesarik@suse.com>,
        YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Nikolay Borisov <nborisov@suse.com>, richard.weiyang@gmail.com
Subject: Re: [PATCH v9 0/6] optimize memblock_next_valid_pfn and
 early_pfn_valid on arm and arm64
Message-ID: <20180702114037.GJ19043@dhcp22.suse.cz>
References: <1530239363-2356-1-git-send-email-hejianet@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1530239363-2356-1-git-send-email-hejianet@gmail.com>
User-Agent: Mutt/1.10.0 (2018-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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