From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754213Ab2K2Lgn (ORCPT ); Thu, 29 Nov 2012 06:36:43 -0500 Received: from mail-bk0-f46.google.com ([209.85.214.46]:54887 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752645Ab2K2Lgm (ORCPT ); Thu, 29 Nov 2012 06:36:42 -0500 Date: Thu, 29 Nov 2012 12:36:35 +0100 From: Vasilis Liaskovitis To: "Rafael J. Wysocki" Cc: linux-acpi@vger.kernel.org, Toshi Kani , Hanjun Guo , isimatu.yasuaki@jp.fujitsu.com, wency@cn.fujitsu.com, lenb@kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Tang Chen Subject: Re: [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device operation Message-ID: <20121129113635.GC639@dhcp-192-168-178-175.profitbricks.localdomain> References: <1353693037-21704-1-git-send-email-vasilis.liaskovitis@profitbricks.com> <50B5EFE9.3040206@huawei.com> <1354128096.26955.276.camel@misato.fc.hp.com> <75241306.UQIr1RW8Qh@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <75241306.UQIr1RW8Qh@vostro.rjw.lan> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 29, 2012 at 11:15:31AM +0100, Rafael J. Wysocki wrote: > On Wednesday, November 28, 2012 11:41:36 AM Toshi Kani wrote: > > On Wed, 2012-11-28 at 19:05 +0800, Hanjun Guo wrote: > > > We met the same problem when we doing computer node hotplug, It is a good idea > > > to introduce prepare_remove before actual device removal. > > > > > > I think we could do more in prepare_remove, such as rollback. In most cases, we can > > > offline most of memory sections except kernel used pages now, should we rollback > > > and online the memory sections when prepare_remove failed ? > > > > I think hot-plug operation should have all-or-nothing semantics. That > > is, an operation should either complete successfully, or rollback to the > > original state. > > That's correct. > > > > As you may know, the ACPI based hotplug framework we are working on already addressed > > > this problem, and the way we slove this problem is a bit like yours. > > > > > > We introduce hp_ops in struct acpi_device_ops: > > > struct acpi_device_ops { > > > acpi_op_add add; > > > acpi_op_remove remove; > > > acpi_op_start start; > > > acpi_op_bind bind; > > > acpi_op_unbind unbind; > > > acpi_op_notify notify; > > > #ifdef CONFIG_ACPI_HOTPLUG > > > struct acpihp_dev_ops *hp_ops; > > > #endif /* CONFIG_ACPI_HOTPLUG */ > > > }; > > > > > > in hp_ops, we divide the prepare_remove into six small steps, that is: > > > 1) pre_release(): optional step to mark device going to be removed/busy > > > 2) release(): reclaim device from running system > > > 3) post_release(): rollback if cancelled by user or error happened > > > 4) pre_unconfigure(): optional step to solve possible dependency issue > > > 5) unconfigure(): remove devices from running system > > > 6) post_unconfigure(): free resources used by devices > > > > > > In this way, we can easily rollback if error happens. > > > How do you think of this solution, any suggestion ? I think we can achieve > > > a better way for sharing ideas. :) > > > > Yes, sharing idea is good. :) I do not know if we need all 6 steps (I > > have not looked at all your changes yet..), but in my mind, a hot-plug > > operation should be composed with the following 3 phases. > > > > 1. Validate phase - Verify if the request is a supported operation. All > > known restrictions are verified at this phase. For instance, if a > > hot-remove request involves kernel memory, it is failed in this phase. > > Since this phase makes no change, no rollback is necessary to fail. > > Actually, we can't do it this way, because the conditions may change between > the check and the execution. So the first phase needs to involve execution > to some extent, although only as far as it remains reversible. > > > 2. Execute phase - Perform hot-add / hot-remove operation that can be > > rolled-back in case of error or cancel. > > I would just merge 1 and 2. I agree steps 1 and 2 can be merged, at least for the current ACPI framework. E.g. for memory hotplug, the mm function we call for memory removal (remove_memory) handles both these steps. The new ACPI framework could perhaps expand the operations as Hanjun described, if it makes sense. thanks, - Vasilis