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

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Message-ID: <1466b490-76f8-86a4-f39a-3bef3bb0501f@gmail.com>
Date:   Tue, 3 Jul 2018 10:00:34 +0800
From:   Jia He <hejianet@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
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

Hi Michal
Thanks for the comments

On 7/2/2018 7:40 PM, Michal Hocko Wrote:
> 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.

Ok

> 
>>
>> 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?

hmm.. Currently my answer is no.
But I believe it can shorten the boot time when the memory is larger than n TBs.
-- 
Cheers,
Jia

> [...]
>>  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
>