From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 73F6A6B005C for ; Tue, 25 Aug 2009 21:12:08 -0400 (EDT) Received: by pxi15 with SMTP id 15so6420576pxi.23 for ; Tue, 25 Aug 2009 18:12:06 -0700 (PDT) Message-ID: <4A930313.9070404@vflare.org> Date: Tue, 25 Aug 2009 02:46:03 +0530 From: Nitin Gupta Reply-To: ngupta@vflare.org MIME-Version: 1.0 Subject: Re: [PATCH 1/4] compcache: xvmalloc memory allocator References: <200908241007.47910.ngupta@vflare.org> <84144f020908241033l4af09e7h9caac47d8d9b7841@mail.gmail.com> <4A92EBB4.1070101@vflare.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Hugh Dickins Cc: Pekka Enberg , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-mm-cc@laptop.org List-ID: 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org