linux-kernel - Re: [PATCH v1 2/2] mm/memory_hotplug: remove -EBUSY handling from scan_movable

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Message-ID: <19683dac-3e21-462a-8957-78a0b28b57c4@redhat.com>
Date: Wed, 14 May 2025 21:57:13 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, virtualization@...ts.linux.dev,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Oscar Salvador <osalvador@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Brendan Jackman <jackmanb@...gle.com>, Johannes Weiner <hannes@...xchg.org>,
 Zi Yan <ziy@...dia.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: Re: [PATCH v1 2/2] mm/memory_hotplug: remove -EBUSY handling from
 scan_movable_pages()

On 14.05.25 13:15, David Hildenbrand wrote:
> Now that we can reliably identify PageOffline() pages that allow for
> memory offlining in has_unmovable_pages(), start_isolate_page_range()
> will fail on PageOffline() pages that would prevent memory offlining, and
> we no longer have to detect them in scan_movable_pages() anymore.
> 
> Note that the previous mechanism relied on MEM_GOING_OFFLINE, whereby we
> were not able to distinguish the types of PageOffline() before
> MEM_GOING_OFFLINE.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---

Hmm, I'm having second thoughts about this patch.

With hyper-v, I think we can hotplug partial memory blocks (e.g., 64 
MiB) and online it to ZONE_MOVABLE. These blocks cannot get offlined so 
far -- in contrast to virtio-mem -- and has_unmovable_pages() would not 
identify that.

So probably best to keep that in for now.

-- 
Cheers,

David / dhildenb