Messages in this thread | | | From | Johannes Weiner <> | Subject | Re: [RFC 0/2] Rootmem: boot-time memory allocator | Date | Sun, 04 May 2008 16:17:11 +0200 |
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Hi Yinghai,
Johannes Weiner <hannes@saeurebad.de> writes:
> Hi, > > "Yinghai Lu" <yhlu.kernel@gmail.com> writes: > >> On Sat, May 3, 2008 at 10:54 AM, Ingo Molnar <mingo@elte.hu> wrote: >>> >>> * 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 ;-) >> >> for spanning support node0:0-2g, 4-6g; node1: 2-4g, 6-8g, could have >> some problem. > > Could you eleborate on that? > >> +/* >> + * rootmem_register_node - register a node to rootmem >> + * @nid: node id >> + * @start: first pfn on the node >> + * @end: first pfn after the node >> + * >> + * This function must not be called anymore if the allocator >> + * is already up and running (rootmem_setup() has been called). >> + */ >> +void __init rootmem_register_node(int nid, unsigned long start, >> + unsigned long end) >> +{ >> + BUG_ON(rootmem_functional); >> + >> + if (start < rootmem_min_pfn) >> + rootmem_min_pfn = start; >> + if (end > rootmem_max_pfn) >> + rootmem_max_pfn = end; >> + >> + rootmem_node_pages[nid] = end - start; >> + rootmem_node_offsets[nid] = start; >> + rootmem_nr_nodes++; >> +} >> >> could change rootmem_node_pages/offsets to be struct array with >> offset, pages, and nid. and every node could several struct. and whole >> array should be sorted with nid. > > The whole point is to be agnostic about weird NUMA configs. Right now, > I am pretty proud of the simple data structures and I would avoid > blowing them up again unless there is a hard reason to do so.
One thing I have found is that __rootmem_alloc_node can not garuantee that the memory it returns is on the requested node right now.
I will include the fix in the next version.
Hannes
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