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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 A39ADC4321D for ; Fri, 24 Aug 2018 14:53:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5C3EE21477 for ; Fri, 24 Aug 2018 14:53:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5C3EE21477 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp 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 S1727672AbeHXS2O (ORCPT ); Fri, 24 Aug 2018 14:28:14 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:13944 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726264AbeHXS2N (ORCPT ); Fri, 24 Aug 2018 14:28:13 -0400 Received: from fsav401.sakura.ne.jp (fsav401.sakura.ne.jp [133.242.250.100]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w7OEqR0h006170; Fri, 24 Aug 2018 23:52:27 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav401.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav401.sakura.ne.jp); Fri, 24 Aug 2018 23:52:27 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav401.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157066051.bbtec.net [60.157.66.51]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w7OEqQqf006136 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 24 Aug 2018 23:52:26 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers To: Michal Hocko Cc: =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Andrew Morton , LKML , linux-mm@kvack.org, "David (ChunMing) Zhou" , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , 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, =?UTF-8?Q?Christian_K=c3=b6nig?= , David Rientjes , Leon Romanovsky 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> From: Tetsuo Handa Message-ID: <72844762-7398-c770-1702-f945573f4059@i-love.sakura.ne.jp> Date: Fri, 24 Aug 2018 23:52:25 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180824133207.GR29735@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. >> 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".