On 08/25/2009 02:09 AM, Hugh Dickins wrote: > On Tue, 25 Aug 2009, Nitin Gupta wrote: >> On 08/24/2009 11:03 PM, Pekka Enberg wrote: >>> >>> What's the purpose of passing PFNs around? There's quite a lot of PFN >>> to struct page conversion going on because of it. Wouldn't it make >>> more sense to return (and pass) a pointer to struct page instead? >> >> PFNs are 32-bit on all archs > > Are you sure? If it happens to be so for all machines built today, > I think it can easily change tomorrow. We consistently use unsigned long > for pfn (there, now I've said that, I bet you'll find somewhere we don't!) > > x86_64 says MAX_PHYSMEM_BITS 46 and ia64 says MAX_PHYSMEM_BITS 50 and > mm/sparse.c says > unsigned long max_sparsemem_pfn = 1UL<< (MAX_PHYSMEM_BITS-PAGE_SHIFT); >
For PFN to exceed 32-bit we need to have physical memory > 16TB (2^32 * 4KB). So, maybe I can simply add a check in ramzswap module load to make sure that RAM is indeed < 16TB and then safely use 32-bit for PFN? Thanks, Nitin _______________________________________________ linux-mm-cc mailing list [email protected] http://lists.laptop.org/listinfo/linux-mm-cc
