From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx111.postini.com [74.125.245.111]) by kanga.kvack.org (Postfix) with SMTP id 3A2D76B0032 for ; Thu, 16 May 2013 22:53:49 -0400 (EDT) From: ebiederm@xmission.com (Eric W. Biederman) References: <20130515090507.28109.28956.stgit@localhost6.localdomain6> <51957469.2000008@zytor.com> Date: Thu, 16 May 2013 19:53:31 -0700 In-Reply-To: <51957469.2000008@zytor.com> (H. Peter Anvin's message of "Thu, 16 May 2013 17:06:01 -0700") Message-ID: <87y5bee2qc.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore Sender: owner-linux-mm@kvack.org List-ID: To: "H. Peter Anvin" Cc: HATAYAMA Daisuke , vgoyal@redhat.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 "H. Peter Anvin" writes: > 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". That is completely and totally orthogonal to this change. read_oldmem may have problems but in practice on a large systems those problems are totally dwarfed by real life performance issues that come from playing too much with the page tables. I really don't find bringing up whatever foundational issues you have with read_oldmem() appropriate or relevant here. Eric -- 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