From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from out02.mta.xmission.com ([166.70.13.232]) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1UdAoM-0005QE-Ed for kexec@lists.infradead.org; Fri, 17 May 2013 02:54:27 +0000 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 Subject: Re: [PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=twosheds.infradead.org@lists.infradead.org To: "H. Peter Anvin" Cc: riel@redhat.com, hughd@google.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, lisa.mitchell@hp.com, linux-mm@kvack.org, HATAYAMA Daisuke , kumagai-atsushi@mxc.nes.nec.co.jp, jingbai.ma@hp.com, kosaki.motohiro@jp.fujitsu.com, zhangyanfei@cn.fujitsu.com, akpm@linux-foundation.org, walken@google.com, cpw@sgi.com, vgoyal@redhat.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 _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec