Re: [PATCH v9 0/6] optimize memblock_next_valid_pfn and early_pfn_valid on arm and arm64

From: Jia He <hejianet@gmail.com>
To: Michal Hocko <mhocko@kernel.org>
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
Date: Tue, 3 Jul 2018 10:00:34 +0800	[thread overview]
Message-ID: <1466b490-76f8-86a4-f39a-3bef3bb0501f@gmail.com> (raw)
In-Reply-To: <20180702114037.GJ19043@dhcp22.suse.cz>

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
>