From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f69.google.com (mail-oi0-f69.google.com [209.85.218.69]) by kanga.kvack.org (Postfix) with ESMTP id C9CD56B3033 for ; Fri, 24 Aug 2018 10:52:47 -0400 (EDT) Received: by mail-oi0-f69.google.com with SMTP id x145-v6so4306155oia.10 for ; Fri, 24 Aug 2018 07:52:47 -0700 (PDT) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id o64-v6si4960190oih.242.2018.08.24.07.52.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 24 Aug 2018 07:52:46 -0700 (PDT) Subject: Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers 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 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: owner-linux-mm@kvack.org List-ID: 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 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 JA(C)rA'me about mm/hmm.c changes".