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:   Thu, 22 Mar 2018 13:52:04 +0100
From:   Eugeniu Rosca <erosca@de.adit-jv.com>
To:     Jia He <hejianet@gmail.com>
CC:     Daniel Vacek <neelx@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mel Gorman <mgorman@suse.de>,
        Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.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>,
        Vlastimil Babka <vbabka@suse.cz>,
        open list <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>, <x86@kernel.org>,
        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>,
        Jia He <jia.he@hxt-semitech.com>,
        Eugeniu Rosca <erosca@de.adit-jv.com>
Subject: Re: [PATCH 1/4] mm: page_alloc: reduce unnecessary binary search in
 memblock_next_valid_pfn()
Message-ID: <20180322125204.GA8892@vmlxhi-102.adit-jv.com>
References: <1521619796-3846-1-git-send-email-hejianet@gmail.com>
 <1521619796-3846-2-git-send-email-hejianet@gmail.com>
 <CACjP9X92M3izDD-1s1vY6n6Hx3mxqNqeM4f+T3RNnBo8kjP4Qg@mail.gmail.com>
 <3f208ebe-572f-f2f6-003e-5a9cf49bb92f@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <3f208ebe-572f-f2f6-003e-5a9cf49bb92f@gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Mar 21, 2018 at 08:28:18PM +0800, Jia He wrote:
> 
> 
> On 3/21/2018 6:14 PM, Daniel Vacek Wrote:
> >On Wed, Mar 21, 2018 at 9:09 AM, Jia He <hejianet@gmail.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. if pfn and pfn+1 are in the same
> >>memblock region, we can simply pfn++ instead of doing the binary search
> >>in memblock_next_valid_pfn.
> >There is a revert-mm-page_alloc-skip-over-regions-of-invalid-pfns-where-possible.patch
> >in -mm reverting b92df1de5d289c0b as it is fundamentally wrong by
> >design causing system panics on some machines with rare but still
> >valid mappings. Basically it skips valid pfns which are outside of
> >usable memory ranges (outside of memblock memory regions).
> Thanks for the infomation.
> quote from you patch description:
> >But given some specific memory mapping on x86_64 (or more generally
> theoretically anywhere but on arm with CONFIG_HAVE_ARCH_PFN_VALID) > the
> implementation also skips valid pfns which is plain wrong and causes >
> 'kernel BUG at mm/page_alloc.c:1389!'
> 
> Do you think memblock_next_valid_pfn can remain to be not reverted on arm64
> with CONFIG_HAVE_ARCH_PFN_VALID? Arm64 can benifit from this optimization.

I confirm that the boot time of Rcar-H3 arm64 platform greatly
benefits from v4.11-rc1 commit b92df1de5d28 ("mm: page_alloc: skip over
regions of invalid pfns where possible"). The startup improvement is
roughly ~140ms, which will be lost if the mentioned commit is reverted.

For more details on my measurements, please see linux-next commit
283f1645e236 ("mm: page_alloc: skip over regions of invalid pfns on
UMA").

Whichever way you decide to go forward (reimplement/fix b92df1de5d28
or create an <arch>_next_valid_pfn), I am willing to participate in
testing your proposals on RCAR SoCs. TIA.

Thanks,
Eugeniu.