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    SubjectRe: [RFC 0/2] Rootmem: boot-time memory allocator
    Date
    Hi,

    Ingo Molnar <mingo@elte.hu> writes:

    > * Johannes Weiner <hannes@saeurebad.de> wrote:
    >
    >> I was spending some time and work on the bootmem allocator the last
    >> few weeks and came to the conclusion that its current design is not
    >> appropriate anymore.
    >>
    >> As Ingo said in another email, NUMA technologies will become weirder,
    >> nodes whose PFNs span other nodes for example and it makes bootmem
    >> code become an unreadable mess.
    >>
    >> So I sat down two days ago and rewrote the allocator, here is the
    >> result: rootmem!
    >
    > hehe :-)
    >
    >> The biggest difference to the old design is that there is only one
    >> bitmap for all PFNs of all nodes together, so the overlapping PFN
    >> problems simply dissolve and fun like allocations crossing node
    >> boundaries work implicitely. The new API requires every node used by
    >> the allocator to be registered and after that the bitmap gets
    >> allocated and the allocator enabled.
    >>
    >> I chose to add a new allocator rather than replacing bootmem at once
    >> because that would have required all callsites to switch in one go,
    >> which would be a lot. The new allocator can be adopted more slowly
    >> and I added a compatibility API for everything besides actually
    >> setting up the allocator. When the last user dies, bootmem can be
    >> dropped completely (including pgdat->bdata, whee..)
    >>
    >> The main ideas from bootmem have been stolen^W preserved but the new
    >> design allowed me to shrink the code a lot and express things more
    >> simple and clear:
    >>
    >> $ sloc.awk < mm/bootmem.c
    >> 455 lines of code, 65 lines of comments (520 lines total)
    >>
    >> $ sloc.awk < mm/rootmem.c
    >> 243 lines of code, 96 lines of comments (339 lines total)
    >
    > amazing!
    >
    > i'd still suggest to keep it all named bootmem though :-/ How about
    > bootmem2.c and then renaming it back to bootmem.c, once the last user is
    > gone? That would save people from having to rename whole chapters in
    > entire books ;-)

    Hehe, I still have bootmem2.c flying around... I was not sure if the
    migration is easier with the same name or with a different name but the
    API is mostly compatible in the end, so staying with bootmem should be
    possible and it sounds way better...

    Hannes


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