linux-kernel - Re: [PATCH v1 2/4] memblock: allow to specify flags with memblock_add

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Message-ID: <3651c7d0-f7b6-63ff-216a-b74176623a6f@redhat.com>
Date:   Wed, 29 Sep 2021 18:30:09 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Jianyong Wu <Jianyong.Wu@....com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Vineet Gupta <vgupta@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-snps-arc@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-mm@...ck.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH v1 2/4] memblock: allow to specify flags with
 memblock_add_node()

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