linux-kernel - Re: [PATCH v4 6/6] memblock: Disable mirror feature if kernelcore is not specified

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Date:   Mon, 13 Jun 2022 19:54:53 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Ard Biesheuvel <ardb@...nel.org>, Mike Rapoport <rppt@...nel.org>
CC:     Wupeng Ma <mawupeng1@...wei.com>, <corbet@....net>,
        <will@...nel.org>, <catalin.marinas@....com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
        <x86@...nel.org>, <hpa@...or.com>, <dvhart@...radead.org>,
        <andy@...radead.org>, <akpm@...ux-foundation.org>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <paulmck@...nel.org>,
        <keescook@...omium.org>, <songmuchun@...edance.com>,
        <rdunlap@...radead.org>, <damien.lemoal@...nsource.wdc.com>,
        <swboyd@...omium.org>, <wei.liu@...nel.org>,
        <robin.murphy@....com>, <david@...hat.com>,
        <anshuman.khandual@....com>, <thunder.leizhen@...wei.com>,
        <gpiccoli@...lia.com>, <chenhuacai@...nel.org>,
        <geert@...ux-m68k.org>, <vijayb@...ux.microsoft.com>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-efi@...r.kernel.org>, <platform-driver-x86@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v4 6/6] memblock: Disable mirror feature if kernelcore is
 not specified


On 2022/6/13 19:25, Ard Biesheuvel wrote:
> On Mon, 13 Jun 2022 at 13:05, Mike Rapoport <rppt@...nel.org> wrote:
>> On Mon, Jun 13, 2022 at 04:21:47PM +0800, Wupeng Ma wrote:
>>> From: Ma Wupeng <mawupeng1@...wei.com>
>>>
>>> If system have some mirrored memory and mirrored feature is not specified
>>> in boot parameter, the basic mirrored feature will be enabled and this will
>>> lead to the following situations:
>>>
>>> - memblock memory allocation prefers mirrored region. This may have some
>>>    unexpected influence on numa affinity.
>>>
>>> - contiguous memory will be split into several parts if parts of them
>>>    is mirrored memory via memblock_mark_mirror().
...
> Also, on second thought, I don't think marking as mirror is what
> should be affected by the policy. Instead, choose_memblock_flags()
> should take this into account, in a way that we could refine later if
> needed.
> .

The choose_memblock_flags() only solve the issue of memblock allocation, but

the memblock could be splitted and fragmentized, the kernel won't treat the

mirror memory as special if no mirrored_kernelcore for now, so I think 
we'd better

to add the check into memblock_mark_mirror().