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Subject: Re: [PATCH v1 2/4] memblock: allow to specify flags with
 memblock_add_node()
To:     Mike Rapoport <rppt@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Oscar Salvador <osalvador@suse.de>,
        Jianyong Wu <Jianyong.Wu@arm.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        Vineet Gupta <vgupta@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Huacai Chen <chenhuacai@kernel.org>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Arnd Bergmann <arnd@arndb.de>,
        linux-snps-arc@lists.infradead.org, linux-ia64@vger.kernel.org,
        linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-mm@kvack.org,
        kexec@lists.infradead.org
References: <20210927150518.8607-1-david@redhat.com>
 <20210927150518.8607-3-david@redhat.com> <YVSTkGdh2nQWQp+U@kernel.org>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <3651c7d0-f7b6-63ff-216a-b74176623a6f@redhat.com>
Date:   Wed, 29 Sep 2021 18:30:09 +0200
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On 29.09.21 18:25, Mike Rapoport wrote:
> On Mon, Sep 27, 2021 at 05:05:16PM +0200, David Hildenbrand wrote:
>> We want to specify flags when hotplugging memory. Let's prepare to pass
>> flags to memblock_add_node() by adjusting all existing users.
>>
>> Note that when hotplugging memory the system is already up and running
>> and we don't want to add the memory first and apply flags later: it
>> should happen within one memblock call.
> 
> Why is it important that the system is up and why it should happen in a
> single call?
> I don't mind adding flags parameter to memblock_add_node() but this
> changelog does not really explain the reasons to do it.

"After memblock_add_node(), we could race with anybody performing a 
search for MEMBLOCK_NONE, like kexec_file -- and that only happens once 
the system is already up and running. So we want both steps to happen 
atomically."

I can add that to the patch description.

(I think it still won't be completely atomic because memblock isn't 
properly implementing locking yet, but that's a different story)

-- 
Thanks,

David / dhildenb