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Date: Mon, 2 Apr 2018 16:12:33 +0800
From: Wei Yang <richard.weiyang@gmail.com>
Subject: Re: [PATCH v3 1/5] mm: page_alloc: remain memblock_next_valid_pfn()
 when CONFIG_HAVE_ARCH_PFN_VALID is enable
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To: Jia He <hejianet@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.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>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, 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>, 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>, 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>

On Wed, Mar 28, 2018 at 05:49:23PM +0800, Jia He wrote:
>
>
>On 3/28/2018 5:18 PM, Wei Yang Wrote:
>> Oops, I should reply this thread. Forget about the reply on another thread.
>> 
>> On Sun, Mar 25, 2018 at 08:02:15PM -0700, Jia He wrote:
>> > Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
>> > where possible") optimized the loop in memmap_init_zone(). But it causes
>> > possible panic bug. So Daniel Vacek reverted it later.
>> > 
>> Why this has a bug? Do you have some link about it?
>> 
>> If the audience could know the potential risk, it would be helpful to review
>> the code and decide whether to take it back.
>Hi Wei
>Paul firstly submit a commit b92df1de5 to improve the loop in
>memmap_init_zone.
>And Daniel tried to fix a bug_on panic issue on X86 in commit 864b75f9d6b
>because
>there is evidence that this bug_on was caused by b92df1de5 [1].
>
>But things didn't get better, 864b75f9d6b caused booting hang issue on
>arm{64} [2]
>So maintainer decided to reverted both b92df1de5 and 864b75f9d6b
>
>[1] https://patchwork.kernel.org/patch/10251145/
>[2] https://lkml.org/lkml/2018/3/14/469

I took some time to look into the discussion, while the root cause seems not
clear now?

-- 
Wei Yang
Help you, Help me