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

* 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 ;-)

Ingo


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