Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752906Ab0GMIHA (ORCPT ); Tue, 13 Jul 2010 04:07:00 -0400 Received: from mail-iw0-f174.google.com ([209.85.214.174]:37720 "EHLO mail-iw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751693Ab0GMIG5 convert rfc822-to-8bit (ORCPT ); Tue, 13 Jul 2010 04:06:57 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=fncJnRN34eq0090PUF5V6WH79P97Qso6vf6D8F6cQM6IrQ1yApYvT40SvnB9FYLUqW y5q1ZEOJEq2BnfI6e5nT6XbkDm7OCWjrEZXL8zs6kg84OVRanAfySjjZuXvyvoPan/93 VSrATkfEU+ve9fK4X2vB5Zs+WJqI+JrZyDTyI= MIME-Version: 1.0 In-Reply-To: <20100713154025.7c60c76b.kamezawa.hiroyu@jp.fujitsu.com> 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> Date: Tue, 13 Jul 2010 17:06:56 +0900 Message-ID: Subject: Re: [RFC] Tight check of pfn_valid on sparsemem From: Minchan Kim To: KAMEZAWA Hiroyuki 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2232 Lines: 69 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. > > Thanks, > -Kame > > -- Kind regards, Minchan Kim -- 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/