From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BE610C433F5 for ; Fri, 24 Aug 2018 16:39:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 750BD2156B for ; Fri, 24 Aug 2018 16:39:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 750BD2156B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728280AbeHXUOZ (ORCPT ); Fri, 24 Aug 2018 16:14:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:34988 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728224AbeHXUOY (ORCPT ); Fri, 24 Aug 2018 16:14:24 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 18869B012; Fri, 24 Aug 2018 16:38:56 +0000 (UTC) Date: Fri, 24 Aug 2018 18:38:53 +0200 From: Michal Hocko To: Tetsuo Handa Cc: =?iso-8859-1?B?Suly9G1l?= Glisse , Andrew Morton , LKML , linux-mm@kvack.org, "David (ChunMing) Zhou" , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Alex Deucher , David Airlie , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Doug Ledford , Jason Gunthorpe , Mike Marciniszyn , Dennis Dalessandro , Sudeep Dutt , Ashutosh Dixit , Dimitri Sivanich , Boris Ostrovsky , Juergen Gross , Andrea Arcangeli , Felix Kuehling , kvm@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-rdma@vger.kernel.org, xen-devel@lists.xenproject.org, Christian =?iso-8859-1?Q?K=F6nig?= , David Rientjes , Leon Romanovsky Subject: Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers Message-ID: <20180824163853.GV29735@dhcp22.suse.cz> References: <20180716115058.5559-1-mhocko@kernel.org> <8cbfb09f-0c5a-8d43-1f5e-f3ff7612e289@I-love.SAKURA.ne.jp> <20180824113629.GI29735@dhcp22.suse.cz> <103b1b33-1a1d-27a1-dcf8-5c8ad60056a6@i-love.sakura.ne.jp> <20180824133207.GR29735@dhcp22.suse.cz> <72844762-7398-c770-1702-f945573f4059@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <72844762-7398-c770-1702-f945573f4059@i-love.sakura.ne.jp> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 24-08-18 23:52:25, Tetsuo Handa wrote: > On 2018/08/24 22:32, Michal Hocko wrote: > > On Fri 24-08-18 22:02:23, Tetsuo Handa wrote: > >> I worry that (currently > >> out-of-tree) users of this API are involving work / recursion. > > > > I do not give a slightest about out-of-tree modules. They will have to > > accomodate to the new API. I have no problems to extend the > > documentation and be explicit about this expectation. > > You don't need to care about out-of-tree modules. But you need to hear from > mm/hmm.c authors/maintainers when making changes for mmu-notifiers. > > > diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h > > index 133ba78820ee..698e371aafe3 100644 > > --- a/include/linux/mmu_notifier.h > > +++ b/include/linux/mmu_notifier.h > > @@ -153,7 +153,9 @@ struct mmu_notifier_ops { > > * > > * If blockable argument is set to false then the callback cannot > > * sleep and has to return with -EAGAIN. 0 should be returned > > - * otherwise. > > + * otherwise. Please note that if invalidate_range_start approves > > + * a non-blocking behavior then the same applies to > > + * invalidate_range_end. > > Prior to 93065ac753e44438 ("mm, oom: distinguish blockable mode for mmu > notifiers"), whether to utilize MMU_INVALIDATE_DOES_NOT_BLOCK was up to > mmu-notifiers users. > > - * If both of these callbacks cannot block, and invalidate_range > - * cannot block, mmu_notifier_ops.flags should have > - * MMU_INVALIDATE_DOES_NOT_BLOCK set. > + * If blockable argument is set to false then the callback cannot > + * sleep and has to return with -EAGAIN. 0 should be returned > + * otherwise. > > Even out-of-tree mmu-notifiers users had rights not to accommodate (i.e. > make changes) immediately by not setting MMU_INVALIDATE_DOES_NOT_BLOCK. > > Now we are in a merge window. And we noticed a possibility that out-of-tree > mmu-notifiers users might have trouble with making changes immediately in order > to follow 93065ac753e44438 if expectation for mm/hmm.c changes immediately. > And you are trying to ignore such possibility by just updating expected behavior > description instead of giving out-of-tree users a grace period to check and update > their code. This is just ridiculous. I have no idea what you are trying to achieve here but please read through Documentation/process/stable-api-nonsense.rst before you try to make strong statements again. I have changed an in-kernel interface. I have gone through all users and fixed them up. It is really appreciated to double check after me and I am willing to fix up any fallouts. But that is just about it. I do not get a whit about _any_ out of tree drivers when changing the interface. I am willing to answer any questions regarding this change so developers of those drivers know how to do their change properly but doing so is completely their business. > >> and keeps "all operations protected by hmm->mirrors_sem held for write are > >> atomic". This suggests that "some operations protected by hmm->mirrors_sem held > >> for read will sleep (and in the worst case involves memory allocation > >> dependency)". > > > > Yes and so what? The clear expectation is that neither of the range > > notifiers do not sleep in !blocking mode. I really fail to see what you > > are trying to say. > > I'm saying "Get ACK from Jérôme about mm/hmm.c changes". HMM is a library layer for other driver, until those get merged the same applies for them as well. -- Michal Hocko SUSE Labs