From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx150.postini.com [74.125.245.150]) by kanga.kvack.org (Postfix) with SMTP id 92FFD6B0032 for ; Thu, 16 May 2013 21:46:41 -0400 (EDT) Received: from m2.gw.fujitsu.co.jp (unknown [10.0.50.72]) by fgwmail5.fujitsu.co.jp (Postfix) with ESMTP id D97953EE0C0 for ; Fri, 17 May 2013 10:46:39 +0900 (JST) Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id C918845DE54 for ; Fri, 17 May 2013 10:46:39 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id B1D2145DE4D for ; Fri, 17 May 2013 10:46:39 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id A4DA81DB803C for ; Fri, 17 May 2013 10:46:39 +0900 (JST) Received: from m1000.s.css.fujitsu.com (m1000.s.css.fujitsu.com [10.240.81.136]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 58A921DB8038 for ; Fri, 17 May 2013 10:46:39 +0900 (JST) Message-ID: <51958BC0.207@jp.fujitsu.com> Date: Fri, 17 May 2013 10:45:36 +0900 From: HATAYAMA Daisuke MIME-Version: 1.0 Subject: Re: [PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore References: <20130515090507.28109.28956.stgit@localhost6.localdomain6> <51957469.2000008@zytor.com> In-Reply-To: <51957469.2000008@zytor.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "H. Peter Anvin" Cc: vgoyal@redhat.com, ebiederm@xmission.com, akpm@linux-foundation.org, cpw@sgi.com, kumagai-atsushi@mxc.nes.nec.co.jp, lisa.mitchell@hp.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, zhangyanfei@cn.fujitsu.com, jingbai.ma@hp.com, linux-mm@kvack.org, riel@redhat.com, walken@google.com, hughd@google.com, kosaki.motohiro@jp.fujitsu.com (2013/05/17 9:06), H. Peter Anvin wrote: > On 05/15/2013 02:05 AM, HATAYAMA Daisuke wrote: >> Currently, read to /proc/vmcore is done by read_oldmem() that uses >> ioremap/iounmap per a single page. For example, if memory is 1GB, >> ioremap/iounmap is called (1GB / 4KB)-times, that is, 262144 >> times. This causes big performance degradation. > > read_oldmem() is fundamentally broken and unsafe. It needs to be > unified with the plain /dev/mem code and any missing functionality fixed > instead of "let's just do a whole new driver". > > -hpa Do you mean range_is_allowed should be extended so that it checks according to memory map passed from the 1st kernel? BTW, read request to read_oldmem via read_vmcore and mmap on some part of the 1st kernel, seems safe since it's always restrected to within the memory map. Or is there other missing point? -- Thanks. HATAYAMA, Daisuke -- 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