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

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Message-ID: <20190403085042.t5wcyvaolxiw65rr@d104.suse.de>
Date:   Wed, 3 Apr 2019 10:50:42 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     David Hildenbrand <david@...hat.com>
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 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.

-- 
Oscar Salvador
SUSE L3