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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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