linux-kernel - Re: [PATCH 0/4] mm,memory_hotplug: allocate memmap from hotadded memory

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Message-ID: <815a98e1-3b2e-e5c8-5074-7f46a363adb8@redhat.com>
Date:   Wed, 3 Apr 2019 10:54:28 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Michal Hocko <mhocko@...nel.org>, akpm@...ux-foundation.org,
        dan.j.williams@...el.com, Jonathan.Cameron@...wei.com,
        anshuman.khandual@....com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 0/4] mm,memory_hotplug: allocate memmap from hotadded
 memory

On 03.04.19 10:50, Oscar Salvador wrote:
> On Wed, Apr 03, 2019 at 10:41:35AM +0200, David Hildenbrand wrote:
>>> That being said it should be the caller of the hotplug code to tell
>>> the vmemmap allocation strategy. For starter, I would only pack vmemmaps
>>> for "regular" kernel zone memory. Movable zones should be more careful.
>>> We can always re-evaluate later when there is a strong demand for huge
>>> pages on movable zones but this is not the case now because those pages
>>> are not really movable in practice.
>>
>> Remains the issue with potential different user trying to remove memory
>> it didn't add in some other granularity. We then really have to identify
>> and isolate that case.
> 
> If we let the caller specify whether it wants vmemmaps per memblock or range,
> I would trust that caller to do the correct thing and specify one thing or
> another depending on what it wants to do in the future.
> 
> So, say a driver adds 512MB memory and it specifies that it wants vmemmaps per
> memblock because later on it will like to hot-remove in chunks of 128MB.
> 

I am talking about the memtrace and ACPI thing. Otherwise I agree, trust
the user iff the user is the same person adding/removing memory.

-- 

Thanks,

David / dhildenb