From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx202.postini.com [74.125.245.202]) by kanga.kvack.org (Postfix) with SMTP id 8579B6B0032 for ; Thu, 16 May 2013 20:06:31 -0400 (EDT) Message-ID: <51957469.2000008@zytor.com> Date: Thu, 16 May 2013 17:06:01 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore References: <20130515090507.28109.28956.stgit@localhost6.localdomain6> In-Reply-To: <20130515090507.28109.28956.stgit@localhost6.localdomain6> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: HATAYAMA Daisuke 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 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 -- 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