linux-kernel - Re: [PATCH v2 resend] mm/memory_hotplug: Make unpopulated zones PCP structures unreachable during hot remove

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Message-ID: <b1243b7b-fa4c-496f-5bfc-c83c7cee81cf@suse.cz>
Date:   Tue, 13 Apr 2021 11:36:08 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Alexander Duyck <alexanderduyck@...com>,
        Minchan Kim <minchan@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 resend] mm/memory_hotplug: Make unpopulated zones PCP
 structures unreachable during hot remove

On 4/12/21 4:08 PM, Mel Gorman wrote:
> On Mon, Apr 12, 2021 at 02:40:18PM +0200, Vlastimil Babka wrote:
>> On 4/12/21 2:08 PM, Mel Gorman wrote:
>
> the pageset structures in place would be much more straight-forward
> assuming the structures were not allocated in the zone that is being
> hot-removed.

I would expect this is not possible, at least for ZONE_MOVABLE, as the percpu
allocations should be GFP_KERNEL. And it's not realistic to expect offlining to
succeed at all without using ZONE_MOVABLE.

AFAIK even Oscar's work on using the node to self-contain its own structures is
only applicable to struct pages, not percpu allocations?