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    SubjectRe: [PATCH v2 2/4] mm: handle uninitialized numa nodes gracefully
    On Tue 14-12-21 11:33:41, Christoph Lameter wrote:
    > 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.

    This is certainly possible but also it is more complex. I aim for as
    simple as possible at this stage. The reason I am not concerned about
    memory overhead so much (even though the pgdat is a large data
    structure) is that these unpopulated nodes are rather rare. We might see
    more of them in the future but we are not quite there yet so I do not
    think this is a major obstacle for now.

    --
    Michal Hocko
    SUSE Labs

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