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=-13.2 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,URIBL_BLOCKED,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 6A0C2C433DB for ; Tue, 22 Dec 2020 17:49:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BE3B230FC for ; Tue, 22 Dec 2020 17:49:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728098AbgLVRtg (ORCPT ); Tue, 22 Dec 2020 12:49:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42282 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727988AbgLVRtg (ORCPT ); Tue, 22 Dec 2020 12:49:36 -0500 Received: from mail-wm1-x329.google.com (mail-wm1-x329.google.com [IPv6:2a00:1450:4864:20::329]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 60ACDC0613D3 for ; Tue, 22 Dec 2020 09:48:55 -0800 (PST) Received: by mail-wm1-x329.google.com with SMTP id 190so2549103wmz.0 for ; Tue, 22 Dec 2020 09:48:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=gZ3Mpnz+y+y40eMwZF/PF9p0ykrXNof+TnqSLHPYMc4=; b=fJurTTnF+Va0FHUdyTWNlS1cGpvh5djyhWHIz8cfeXiEfOyaHauqRQAM7CWWF/HB4r XIFtvR6qpYy5MgmX/TledRqo+t3vH2fcKr7e38xsmzAyKFWgAU8vhI2ZUIFIAYsEkZ8p a1YloLSV7hKc5+Gwt6KP7k500IbltONvgsDcSeGi9zSpQg8zA7YgsqoHX5zOYwp5BF/e iW/jP7UOFR0ATiu/JRaMsx7mEMPFpD1OoYVYpfMH/SAtbBGfvYXc6oIG88gZL0BbXR1o FAp5U+WxGka2LA/evqmWwrzWueuV0cQwOyeE9XZRiQIJnFQm1w0/OvkqpZyWL+tQoCmU sZBQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=gZ3Mpnz+y+y40eMwZF/PF9p0ykrXNof+TnqSLHPYMc4=; b=BuzdlBnsngYr8FBQwwm9LwuJYJ51Dzq72OSvHd4avrendY7MhZFtYGAKbHlSgrFNsU VP4O06xbzDhXbnnroZXYs/o3HQOEMxwzXOrEjh8x7YorU8wwqqvf+0DwURqa0nZJVXzh 8nG6FA6GKXzgKQS6Ds+FIt/C5Ee8ZMfk2Kx+k3gk+T9punNJdYrSYLuv4ZPHqpe3HDX8 RacJrCwvkHYkIBPKw7NsG62+1xBAj0uNeF+JZ32v4E7irz/LInMNbqNDBCRQfHzwqWZK yNpZBItlee7zHiDveBiRsia5w5573GNc2VZwCn9un436tdtm/8HIsiZlnCSi8BWeqCpC meWQ== X-Gm-Message-State: AOAM532Ckw6/3bIC6J/WQ4F+IIScP5OCw83iyoiEw8NrJqdcES22/zKb iTmdsyj7NgMJjxKog2MsrH3y+x5kTW7FogZUkEyJbA== X-Google-Smtp-Source: ABdhPJx8xdo+vZEMkO7jQEED2nsivqCj2PRiduHKYZoEitQJoXN17y7RtUWzBp4kXUmTBuo5w4edqoIkhNfbujhKVnY= X-Received: by 2002:a1c:4e0a:: with SMTP id g10mr22732565wmh.88.1608659333913; Tue, 22 Dec 2020 09:48:53 -0800 (PST) MIME-Version: 1.0 References: <20201124053943.1684874-1-surenb@google.com> <20201124053943.1684874-2-surenb@google.com> <20201125231322.GF1484898@google.com> <20201222134438.GA7170@infradead.org> In-Reply-To: <20201222134438.GA7170@infradead.org> From: Suren Baghdasaryan Date: Tue, 22 Dec 2020 09:48:43 -0800 Message-ID: Subject: Re: [PATCH 1/2] mm/madvise: allow process_madvise operations on entire memory range To: Christoph Hellwig Cc: Jann Horn , Minchan Kim , Christoph Hellwig , Andrew Morton , Michal Hocko , Michal Hocko , David Rientjes , Matthew Wilcox , Johannes Weiner , Roman Gushchin , Rik van Riel , Christian Brauner , Oleg Nesterov , Tim Murray , Linux API , Linux-MM , kernel list , kernel-team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Tue, Dec 22, 2020 at 5:44 AM Christoph Hellwig wrote: > > On Fri, Dec 11, 2020 at 09:27:46PM +0100, Jann Horn wrote: > > > Can we just use one element in iovec to indicate entire address rather > > > than using up the reserved flags? > > > > > > struct iovec { > > > .iov_base = NULL, > > > .iov_len = (~(size_t)0), > > > }; > > > > In addition to Suren's objections, I think it's also worth considering > > how this looks in terms of compat API. If a compat process does > > process_madvise() on another compat process, it would be specifying > > the maximum 32-bit number, rather than the maximum 64-bit number, so > > you'd need special code to catch that case, which would be ugly. > > > > And when a compat process uses this API on a non-compat process, it > > semantically gets really weird: The actual address range covered would > > be larger than the address range specified. > > > > And if we want different access checks for the two flavors in the > > future, gating that different behavior on special values in the iovec > > would feel too magical to me. > > > > And the length value SIZE_MAX doesn't really make sense anyway because > > the length of the whole address space would be SIZE_MAX+1, which you > > can't express. > > > > So I'm in favor of a new flag, and strongly against using SIZE_MAX as > > a magic number here. > > Yes, using SIZE_MAX is a horrible interface in this case. I'm not > a huge fan of a flag either. What is the use case for the madvise > to all of a processes address space anyway? Thanks for the feedback! The use case is userspace memory reaping similar to oom-reaper. Detailed justification is here: https://lore.kernel.org/linux-mm/20201124053943.1684874-1-surenb@google.com