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

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Message-ID: <20190403084915.GF15605@dhcp22.suse.cz>
Date:   Wed, 3 Apr 2019 10:49:15 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Oscar Salvador <osalvador@...e.de>, 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 03-04-19 10:41:35, David Hildenbrand wrote:
> On 03.04.19 10:37, Michal Hocko 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.

Can you give an example of a sensible usecase that would require this?
-- 
Michal Hocko
SUSE Labs