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

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Message-ID: <20190403094054.jdr7lxm45htgcsk7@d104.suse.de>
Date:   Wed, 3 Apr 2019 11:40:54 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     David Hildenbrand <david@...hat.com>, 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 10:37:57AM +0200, 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.

I agree that makes sense to let the caller specify if it wants to allocate
vmemmaps per memblock or per memory-range, so we are more flexible when it
comes to granularity in hot-add/hot-remove operations.

But the thing is that the zones are picked at onling stage, while
vmemmaps are created at hot-add stage, so I am not sure we can define
the strategy depending on the zone.

-- 
Oscar Salvador
SUSE L3