[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] RE: [Question] Why code differs in construct_dom0?
Keir Fraser wrote: > On 20/11/08 09:41, "Shan, Haitao" <haitao.shan@xxxxxxxxx> wrote: > >> So you mean in the release build we make the mapping discontiguous >> to detect possible bugs, while in debug build it is not >> discontiguous? > > It's the other way round. > >> And another question from problems we encountered recently, system >> with more than 4G memory installed will crash when X server >> shutdown. The reason is: 1> dom0 allocates memory for agp by calling >> agp_allocate_memory with GFP_DMA32 set. This implies the pfn comes >> from memory lower than 4G, while mfn are likely to be from memory >> above 4G. 2> dom0 then call map_pages_to_apg, since the kernel of >> handles 32bit gart table, dom0 uses hypercall to change its memory >> mappings (xen_create_contiguous_region). Xen will pick proper memory >> below 4G and free those from the guest (likely to be from memory >> above 4G). 3> As the process goes on. More and more memory below 4G >> is return to dom0 while leaving memory above 4G in xen. Finally, >> xen's reservation of memory below 4G for DMA are exhausted. This >> creates severe problems for us. >> >> What is your comments on this? Both increase the reservation in Xen >> and using contiguous mappings are helpful in this cases. Which one >> do you prefer? > > I'd need more info on the problem. I will point out that 64-bit Xen > only allocates memory below 4G when asked, or when there is no memory > available above 4G. Actually 32-bit Xen is the same, except the first > chunk of dom0 memory allocated has to be below 1GB (because of > limitations of Xen's domain_build.c). So I'm not sure what more Xen > can do? In our problem, most of memory is allocate to dom0 by not specifying dom0_mem=xxx in grub. Dom0 actually has near 4G memory. So in this case, xen only has little memory below 4G, which is from the reservation pool. > > -- Keir > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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