Date:   Tue, 14 Dec 2021 11:33:41 +0100 (CET)
From:   Christoph Lameter <cl@gentwo.org>
To:     Michal Hocko <mhocko@kernel.org>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Alexey Makhalov <amakhalov@vmware.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        Dennis Zhou <dennis@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Oscar Salvador <osalvador@suse.de>, Tejun Heo <tj@kernel.org>,
        Nico Pache <npache@redhat.com>, Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v2 2/4] mm: handle uninitialized numa nodes gracefully
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References: <YbHfBgPQMkjtuHYF@dhcp22.suse.cz> <20211214100732.26335-1-mhocko@kernel.org> <20211214100732.26335-3-mhocko@kernel.org>
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On Tue, 14 Dec 2021, Michal Hocko wrote:

> This patch takes a different approach (following a lead of [3]) and it
> pre allocates pgdat for all possible nodes in an arch indipendent code
> - free_area_init. All uninitialized nodes are treated as memoryless
> nodes. node_state of the node is not changed because that would lead to
> other side effects - e.g. sysfs representation of such a node and from
> past discussions [4] it is known that some tools might have problems
> digesting that.

Would it be possible to define a pgdat statically and place it in read
only memory? Populate with values that ensure that the page allocator
does not blow up but does a defined fallback.

Point the pgdat for all nodes not online to that readonly pgdat?

Maybe that would save some memory. When the node comes online then a real
pgdat could be allocated.