linux-kernel - Re: [PATCH 2/6] mm: handle uninitialized numa nodes gracefully

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Date:   Fri, 28 Jan 2022 07:27:09 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        Alexey Makhalov <amakhalov@...are.com>,
        Dennis Zhou <dennis@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Nico Pache <npache@...hat.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Rafael Aquini <raquini@...hat.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 2/6] mm: handle uninitialized numa nodes gracefully

On 2022-01-27 09:53, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> We have had several reports [1][2][3] that page allocator blows up when
> an allocation from a possible node is requested. The underlying reason
> is that NODE_DATA for the specific node is not allocated.
> 
> NUMA specific initialization is arch specific and it can vary a lot.
> E.g. x86 tries to initialize all nodes that have some cpu affinity (see
> init_cpu_to_node) but this can be insufficient because the node might 
> be
> cpuless for example.
> 
> One way to address this problem would be to check for !node_online 
> nodes
> when trying to get a zonelist and silently fall back to another node.
> That is unfortunately adding a branch into allocator hot path and it
> doesn't handle any other potential NODE_DATA users.
> 
> 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.
> 
> Newly allocated pgdat only gets a minimal initialization and the rest 
> of
> the work is expected to be done by the memory hotplug - 
> hotadd_new_pgdat
> (renamed to hotadd_init_pgdat).
> 
> generic_alloc_nodedata is changed to use the memblock allocator because
> neither page nor slab allocators are available at the stage when all
> pgdats are allocated. Hotplug doesn't allocate pgdat anymore so we can
> use the early boot allocator. The only arch specific implementation is
> ia64 and that is changed to use the early allocator as well.
> 
> Reported-by: Alexey Makhalov <amakhalov@...are.com>
> Tested-by: Alexey Makhalov <amakhalov@...are.com>
> Reported-by: Nico Pache <npache@...hat.com>
> Acked-by: Rafael Aquini <raquini@...hat.com>
> Tested-by: Rafael Aquini <raquini@...hat.com>
> Signed-off-by: Michal Hocko <mhocko@...e.com>

With the mentioned fixups:

Reviewed-by: Oscar Salvador <osalvador@...e.de>

-- 
Oscar Salvador
SUSE Labs