From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kanoj Sarcar Message-Id: <200008171907.MAA37675@google.engr.sgi.com> Subject: Re: pte_pagenr/MAP_NR deleted in pre6 Date: Thu, 17 Aug 2000 12:07:12 -0700 (PDT) In-Reply-To: <20000817101121.G4037@redhat.com> from "Stephen C. Tweedie" at Aug 17, 2000 10:11:21 AM MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: "Stephen C. Tweedie" Cc: Roman Zippel , linux-mm@kvack.org, linux-kernel@vger.rutgers.edu, rmk@arm.linux.org.uk, nico@cam.org, davem@redhat.com, davidm@hpl.hp.com, alan@lxorguk.ukuu.org.uk List-ID: > > Hi, > > On Wed, Aug 16, 2000 at 03:22:07PM -0700, Kanoj Sarcar wrote: > > > > It's part of what is necessary if we want to push kiobufs into the > > > driver layers. page_to_pfn is needed to for PAE36 support so that > > > PCI64 or dual-address-cycle drivers can handle physical addresses > > > longer than 32 bits long. > > > > While we are on this topic, something like > > > > #define page_to_phys(page) \ > > ((((page)-(page)->zone->zone_mem_map) << PAGE_SHIFT) \ > > + ((page)->zone->zone_start_paddr)) > > > > should work on all platforms on 2.4. (You might have to add in an > > unsigned long long somewhere in there for PAE36). > > The long long is exactly what we need to avoid: PAE36 still has > pointers as 32-bit values. Only ptes get the 64-bit treatment. > > Adding a BUG() test to detect illegal accesses to >4GB pages on PAE36 > would be fine. If we have the appropriate bounce buffer support in > place in pci_dma or wherever suits it, then by the time a driver is > doing page_to_phys() it should already have created the appropriate > bounce buffers and so the BUG() test is fine. > > For DAC/PCI64 drivers, though, we need a separate macro like > page_to_pfn so that we can identify the physical address via a 32-bit Or, use a 64 bit value to represent physical addresses. Which is why I am proposing paddr_t. In that case, #define page_to_phys(page) ((((unsigned long long)((page)-(page)->zone->zone_mem_map)) \ << PAGE_SHIFT) + ((page)->zone->zone_start_paddr)) This would "work" (on i386) despite the fact that zone->zone_start_paddr is "unsigned long" not "unsigned long long". Things would be much easier with paddr_t. #define page_to_phys(page) ((((paddr_t)((page)-(page)->zone->zone_mem_map)) \ << PAGE_SHIFT) + ((page)->zone->zone_start_paddr)) and we would change zone->zone_start_paddr to be paddr_t too. > value. The driver can then shift that into a 64-bit long long if it > wants to --- there's no need to introduce new 64-bit macros into the > mm just for this special case. Whatever you do, you either have to introduce paddr_t (which to me seems more intuitive) or page_to_pfn. We can argue one way or another, but paddr_t might give you type checking for free too ... Kanoj > > Cheers, > Stephen > -- 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.eu.org/Linux-MM/