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    SubjectRe: [RFC v2 PATCH 0/8] mm: mirrored memory support for page buddy allocations

    * Mel Gorman <mgorman@suse.de> wrote:

    > [...]
    >
    > Basically, overall I feel this series is the wrong approach but not knowing who
    > the users are making is much harder to judge. I strongly suspect that if
    > mirrored memory is to be properly used then it needs to be available before the
    > page allocator is even active. Once active, there needs to be controlled access
    > for allocation requests that are really critical to mirror and not just all
    > kernel allocations. None of that would use a MIGRATE_TYPE approach. It would be
    > alterations to the bootmem allocator and access to an explicit reserve that is
    > not accounted for as "free memory" and accessed via an explicit GFP flag.

    So I think the main goal is to avoid kernel crashes when a #MC memory fault
    arrives on a piece of memory that is owned by the kernel.

    In that sense 'protecting' all kernel allocations is natural: we don't know how to
    recover from faults that affect kernel memory.

    We do know how to recover from faults that affect user-space memory alone.

    So if a mechanism is in place that prioritizes 3 groups of allocators:

    - non-recoverable memory (kernel allocations mostly)

    - high priority user memory (critical apps that must never fail)

    - recoverable user memory (non-dirty caches that can simply be dropped,
    non-critical apps, etc.)

    then we can make use of this hardware feature. I suspect this series tries to move
    in that direction.

    Thanks,

    Ingo


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