Messages in this thread | | | From | Johannes Weiner <> | Subject | Re: [RFC 0/2] Rootmem: boot-time memory allocator | Date | Sun, 04 May 2008 10:57:11 +0200 |
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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.
Hannes
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