Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752982Ab0GMIIe (ORCPT ); Tue, 13 Jul 2010 04:08:34 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:47425 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751253Ab0GMIIc (ORCPT ); Tue, 13 Jul 2010 04:08:32 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Tue, 13 Jul 2010 17:03:42 +0900 From: KAMEZAWA Hiroyuki To: Minchan Kim Cc: linux@arm.linux.org.uk, Yinghai Lu , "H. Peter Anvin" , Andrew Morton , Shaohua Li , Yakui Zhao , linux-kernel@vger.kernel.org, linux-mm@kvack.org, arm-kernel@lists.infradead.org, kgene.kim@samsung.com, Mel Gorman Subject: Re: [RFC] Tight check of pfn_valid on sparsemem Message-Id: <20100713170342.2e9e0b6b.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <20100712155348.GA2815@barrios-desktop> <20100713121947.612bd656.kamezawa.hiroyu@jp.fujitsu.com> <20100713132312.a7dfb100.kamezawa.hiroyu@jp.fujitsu.com> <20100713154025.7c60c76b.kamezawa.hiroyu@jp.fujitsu.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.0.3 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2471 Lines: 65 On Tue, 13 Jul 2010 17:06:56 +0900 Minchan Kim wrote: > On Tue, Jul 13, 2010 at 3:40 PM, KAMEZAWA Hiroyuki > wrote: > > On Tue, 13 Jul 2010 15:04:00 +0900 > > Minchan Kim wrote: > > > >> >> >  2. This can't be help for a case where a section has multiple small holes. > >> >> > >> >> I agree. But this(not punched hole but not filled section problem) > >> >> isn't such case. But it would be better to handle it altogether. :) > >> >> > >> >> > > >> >> > Then, my proposal for HOLES_IN_MEMMAP sparsemem is below. > >> >> > == > >> >> > Some architectures unmap memmap[] for memory holes even with SPARSEMEM. > >> >> > To handle that, pfn_valid() should check there are really memmap or not. > >> >> > For that purpose, __get_user() can be used. > >> >> > >> >> Look at free_unused_memmap. We don't unmap pte of hole memmap. > >> >> Is __get_use effective, still? > >> >> > >> > __get_user() works with TLB and page table, the vaddr is really mapped or not. > >> > If you got SEGV, __get_user() returns -EFAULT. It works per page granule. > >> > >> I mean following as. > >> For example, there is a struct page in on 0x20000000. > >> > >> int pfn_valid_mapped(unsigned long pfn) > >> { > >>        struct page *page = pfn_to_page(pfn); /* hole page is 0x2000000 */ > >>        char *lastbyte = (char *)(page+1)-1;  /* lastbyte is 0x2000001f */ > >>        char byte; > >> > >>        /* We pass this test since free_unused_memmap doesn't unmap pte */ > >>        if(__get_user(byte, page) != 0) > >>                return 0; > > > > why ? When the page size is 4096 byte. > > > >      0x1ffff000 - 0x1ffffffff > >      0x20000000 - 0x200000fff are on the same page. And memory is mapped per page. > > sizeof(struct page) is 32 byte. > So lastbyte is address of struct page + 32 byte - 1. > > > What we access by above __get_user() is a byte at [0x20000000, 0x20000001) > > Right. > > > and it's unmapped if 0x20000000 is unmapped. > > free_unused_memmap doesn't unmap pte although it returns the page to > free list of buddy. > ok, I understood. please see my latest mail and ignore all others. -kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/