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

+/*
+ * 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.

YH


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