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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 2128FC433FE for ; Tue, 14 Sep 2021 18:30:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 09BC4610F9 for ; Tue, 14 Sep 2021 18:30:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230453AbhINSbU (ORCPT ); Tue, 14 Sep 2021 14:31:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39370 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229658AbhINSbS (ORCPT ); Tue, 14 Sep 2021 14:31:18 -0400 Received: from mail-lj1-x234.google.com (mail-lj1-x234.google.com [IPv6:2a00:1450:4864:20::234]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23ABFC061762 for ; Tue, 14 Sep 2021 11:30:00 -0700 (PDT) Received: by mail-lj1-x234.google.com with SMTP id w4so269258ljh.13 for ; Tue, 14 Sep 2021 11:30:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=AFVYzJ8YTa+AGDh1qk1TwKj2W51f7K7hlovDVMVEqy4=; b=NhlGWuGaV0jYGjNbfdOafXTFiTSg+9TM+X1xSh6FvChIKfpetxiyJDG3dyef0TJKiW VSfZ5VINDVFMjKErAw96wZa5KIRdwcSoScZaWLldpalE5xpvALmfN8tDTQ3X0NtRj0wi 3AHBmf7W9aOH+qfOvddVqr7xnUvazkaEPHoLbPIuG3zM8whFPoBwT1PJPefa9FvtYRQw RozofHJugThFbZCpg1QpDvIhOidMo804YW8NiGNB1v8WW8codCAlJYieVM7Bcp0ArNJy ckhoVkQjR0WcOuSilst/EpYecHBlHF/qkKSGVr6jsQ9WFNkBCEpQBlfUbtiP2Dlbq94i 0PRw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=AFVYzJ8YTa+AGDh1qk1TwKj2W51f7K7hlovDVMVEqy4=; b=kRkmW7aGPTQNBy16Xvvs8cA443au4FxUJZu3JND4F1fSZu7dAHgjbwP6hNSIUtWYSm zLPENZgrv84coZ9vG4S5pjGHYgc5pmlaQv6MxAXrKMwdU3FiCiyqoN5ozU/zXfFPdSVN 7zPzxruNilTrEgEk6YNDwSFUaUM9dGZI3bxzJzLGN+MyS3WNCJjN+do6SKBXwAw/8SeJ WudRc697VdgQ9zyZaYgNbDMzMWbO5zAJWs7DU+dslHOXZRfZK+cLpD2tBeSXk2sc0gpg aXgQs6f0rLGT+GlaL8aWbTrNyHKIs5RQuh5QQPWCwgi+s8ZKMgXgYV1x1bSrsTgHVEkd n9Ww== X-Gm-Message-State: AOAM530C42LV4iaesnBM2V/tjcTd3d/2n9Nfw8MF86E8qHnrWfZMpZTy ozflQ/UOqRp+m01YqTHtZ5SJLPbzwhET/u3JzP4Dmw== X-Google-Smtp-Source: ABdhPJwnbfo7jIZV8IhqzpM2WpOdA52Awj/p8tihGDH20IIyaAP+6S+/fyMIIozk856YMAABXV/ZFbjj/GG8Qf+zLRo= X-Received: by 2002:a2e:a726:: with SMTP id s38mr16630655lje.386.1631644198402; Tue, 14 Sep 2021 11:29:58 -0700 (PDT) MIME-Version: 1.0 References: <20210908184905.163787-1-posk@google.com> <20210908184905.163787-3-posk@google.com> In-Reply-To: From: Peter Oskolkov Date: Tue, 14 Sep 2021 11:29:46 -0700 Message-ID: Subject: Re: [PATCH 2/4 v0.5] sched/umcg: RFC: add userspace atomic helpers To: Peter Zijlstra Cc: Jann Horn , Peter Oskolkov , Ingo Molnar , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Paul Turner , Ben Segall , Andrei Vagin , Thierry Delisle Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 14, 2021 at 11:05 AM Peter Zijlstra wrote: > > On Tue, Sep 14, 2021 at 09:29:00AM -0700, Peter Oskolkov wrote: > > In the version of the patchset that I'm preparing to send I've decided > > to punt on the issue and just ask the userspace to deal with locking > > the memory as it sees fit: mlock() is available and as far as I can > > Sadly mlock() does not imply no faults. Someone had a too literal > reading of the POSIX-RT spec (of which mlock is part) and figured that > all that was required was to keep the page in memory, not avoid faults. > > Linux has had this bahviour for ages, PREEMPT_RT has tried to change > this, but so far to no avail. At some point sys_mpin() was proposed to > meet the original POSIX-RT intent, but afaict that never actually > happened. > > In short, mlock() does not avoid minor faults, or even migration faults, > which can take a fair while to resolve. Ok, I'll go with transiently pinning pages in __syscall_enter_from_user_work(), as you suggested. Seems easy enough to do. Thanks for the suggestion!