From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751325Ab2LLF7Q (ORCPT ); Wed, 12 Dec 2012 00:59:16 -0500 Received: from TYO202.gate.nec.co.jp ([210.143.35.52]:36815 "EHLO tyo202.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750864Ab2LLF7P (ORCPT ); Wed, 12 Dec 2012 00:59:15 -0500 Date: Wed, 12 Dec 2012 14:56:31 +0900 From: Atsushi Kumagai To: anderson@redhat.com Cc: vgoyal@redhat.com, akpm@linux-foundation.org, rmk+kernel@arm.linux.org.uk, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, js1304@gmail.com Subject: Re: [RFC PATCH 0/8] remove vm_struct list management Message-Id: <20121212145631.d03a40fd28d4b59b56009fe1@mxc.nes.nec.co.jp> In-Reply-To: <104724866.46130887.1355264225876.JavaMail.root@redhat.com> References: <20121211214859.GG5580@redhat.com> <104724866.46130887.1355264225876.JavaMail.root@redhat.com> X-Mailer: Sylpheed 3.2.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Tue, 11 Dec 2012 17:17:05 -0500 (EST) Dave Anderson wrote: > > > ----- Original Message ----- > > On Mon, Dec 10, 2012 at 11:40:47PM +0900, JoonSoo Kim wrote: > > > > [..] > > > > So without knowing details of both the data structures, I think if vmlist > > > > is going away, then user space tools should be able to traverse vmap_area_root > > > > rb tree. I am assuming it is sorted using ->addr field and we should be > > > > able to get vmalloc area start from there. It will just be a matter of > > > > exporting right fields to user space (instead of vmlist). > > > > > > There is address sorted list of vmap_area, vmap_area_list. > > > So we can use it for traversing vmalloc areas if it is necessary. > > > But, as I mentioned before, kexec write *just* address of vmlist and > > > offset of vm_struct's address field. It imply that they don't traverse vmlist, > > > because they didn't write vm_struct's next field which is needed for traversing. > > > Without vm_struct's next field, they have no method for traversing. > > > So, IMHO, assigning dummy vm_struct to vmlist which is implemented by [7/8] is > > > a safe way to maintain a compatibility of userspace tool. :) > > > > Actually the design of "makedumpfile" and "crash" tool is that they know > > about kernel data structures and they adopt to changes. So for major > > changes they keep track of kernel version numbers and if access the > > data structures accordingly. > > > > Currently we access first element of vmlist to determine start of vmalloc > > address. True we don't have to traverse the list. > > > > But as you mentioned we should be able to get same information by > > traversing to left most element of vmap_area_list rb tree. So I think > > instead of trying to retain vmlist first element just for backward > > compatibility, I will rather prefer get rid of that code completely > > from kernel and let user space tool traverse rbtree. Just export > > minimum needed info for traversal in user space. > > There's no need to traverse the rbtree. There is a vmap_area_list > linked list of vmap_area structures that is also sorted by virtual > address. > > All that makedumpfile would have to do is to access the first vmap_area > in the vmap_area_list -- as opposed to the way that it does now, which is > by accessing the first vm_struct in the to-be-obsoleted vmlist list. > > So it seems silly to keep the dummy "vmlist" around. I think so, I will modify makedumpfile to get the start address of vmalloc with vmap_area_list if the related symbols are provided as VMCOREINFO like vmlist. BTW, have we to consider other tools ? If it is clear, I think we can get rid of the dummy vmlist. Thanks Atsushi Kumagai