On Fri, Sep 14, 2012 at 01:32:23AM +0200, Alexander Graf wrote: > > On 12.09.2012, at 02:34, Paul Mackerras wrote: > > > This series of 3 patches makes it possible for guests to allocate > > whatever size of HPT they need from linear memory preallocated at > > boot, rather than being restricted to a single size of HPT (by > > default, 16MB) and having to use the kernel page allocator for > > anything else -- which in practice limits them to at most 16MB given > > the default value for the maximum page order. Instead of allocating > > many individual pieces of memory, this allocates a single contiguous > > area and uses a simple bitmap-based allocator to hand out pieces of it > > as required. > > Have you tried to play with CMA for this? It sounds like it could buy us exactly what we need. Interesting, I hadn't noticed that there. I had a bit of a look at it, and it's certainly in the right general direction, however it would need some changes to do what we need. It limits the alignment to at most 512 pages, i.e. 2MB with 4k pages or 32MB with 64k pages, but we need RMAs of 64MB to 256MB for PPC970 and they have to be aligned on their size, as do the HPTs for PPC970. Secondly, it has a link with the page allocator that I don't fully understand, but it seems from the comments in alloc_contig_range() (mm/page_alloc.c) that you can allocate at most MAX_ORDER_NR_PAGES pages at once, and that defaults to 16MB for ppc64, which isn't nearly enough. If that's true then it would make it unusable for this. Paul. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
