linux-kernel - Re: [RFC PATCH 0/7] Memory hotplug/hotremove at subsection size

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Date:   Thu, 06 May 2021 11:50:08 -0400
From:   "Zi Yan" <ziy@...dia.com>
To:     "David Hildenbrand" <david@...hat.com>
Cc:     "Oscar Salvador" <osalvador@...e.de>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        "Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
        "Thomas Gleixner" <tglx@...utronix.de>, x86@...nel.org,
        "Andy Lutomirski" <luto@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Mike Rapoport" <rppt@...nel.org>,
        "Anshuman Khandual" <anshuman.khandual@....com>,
        "Michal Hocko" <mhocko@...e.com>,
        "Dan Williams" <dan.j.williams@...el.com>,
        "Wei Yang" <richard.weiyang@...ux.alibaba.com>,
        linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH 0/7] Memory hotplug/hotremove at subsection size

On 6 May 2021, at 11:40, David Hildenbrand wrote:

>>>> The last patch increases SECTION_SIZE_BITS to demonstrate the use of memory
>>>> hotplug/hotremove subsection, but is not intended to be merged as is. It is
>>>> there in case one wants to try this out and will be removed during the final
>>>> submission.
>>>>
>>>> Feel free to give suggestions and comments. I am looking forward to your
>>>> feedback.
>>>
>>> Please not like this.
>>
>> Do you mind sharing more useful feedback instead of just saying a lot of No?
>
> I remember reasoning about this already in another thread, no? Either you're ignoring my previous feedback or my mind is messing with me.

I definitely remember all your suggestions:

1. do not use CMA allocation for 1GB THP.
2. section size defines the minimum size in which we can add_memory(), so we cannot increase it.

I am trying an alternative here. I am not using CMA allocation and not increasing the minimum size of add_memory() by decoupling the memory block size from section size, so that add_memory() can add a memory block smaller (as small as 2MB, the subsection size) than section size. In this way, section size can be increased freely. I do not see the strong tie between add_memory() and section size, especially we have subsection bitmap support.


—
Best Regards,
Yan Zi

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