linux-kernel - Re: [PATCH v2 2/5] mm,memory_hotplug: Introduce MHP_VMEMMAP

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Date:   Thu, 25 Jul 2019 12:15:23 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] mm,memory_hotplug: Introduce MHP_VMEMMAP_FLAGS

On 25.07.19 12:13, Oscar Salvador wrote:
> On Thu, Jul 25, 2019 at 12:04:08PM +0200, David Hildenbrand wrote:
>> As I said somewhere already (as far as I recall), one mode would be
>> sufficient. If you want per memblock, add the memory in memblock
>> granularity.
>>
>> So having a MHP_MEMMAP_ON_MEMORY that allocates it in one chunk would be
>> sufficient for the current use cases (DIMMs, Hyper-V).
>>
>> MHP_MEMMAP_ON_MEMORY: Allocate the memmap for the added memory in one
>> chunk from the beginning of the added memory. This piece of memory will
>> be accessed and used even before the memory is onlined.
> 
> This is what I had in my early versions of the patchset, but I do remember
> that Michal suggested to let the caller specify if it wants the memmaps
> to be allocated per memblock, or per whole-range.
> 
> I still think it makes somse sense, you can just pass a large chunk
> (spanning multiple memory-blocks) at once and yet specify to allocate
> it per memory-blocks.
> 
> Of course, I also agree that having only one mode would ease things
> (not that much as v3 does not suppose that difference wrt. range vs
> memory-block).

I prefer simplicity. No user, no implementation. We can easily add this
later on if there is a good reason/user.

-- 

Thanks,

David / dhildenb